Biology - Questions & Answers CSIR NET Paper II Life-Science

Biology - Questions & Answers

| Anatomy |

What structure of the eye produces tears?

The lachrymal gland, which is part of the larger lachrymal apparatus, produces tears

that flow over the anterior surface of the eye. Most of this fluid evaporates, but excess

amounts are collected in small ducts in the corner of the eye. Tears lubricate and

cleanse the eye. In addition, tears contain lysozyme, an enzyme that is capable of

destroying certain kinds of bacteria and helps fight eye infections.

Why is a man’s voice usually lower than a woman’s voice?

The pitch of the voice—how high or low it sounds—depends on the length, tension, and

thickness of the vocal cords. Because males have longer vocal cords of up to 1 inch

(2.54 centimeters) in length, the male voice is deeper in pitch, while women and

children with shorter cords have higher-pitched voices. Vocal cords in women average

0.167 inches (0.42 centimeters) in length. Testosterone is the hormone that is

responsible for the increase of length of male vocal cords during puberty.

| Anatomy , physiology |

What hormone can be used to overcome jet lag?

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Jet lag occurs when an individual’s biological clock is out of sync with local time. As a

general rule it takes about a day for each hour of time zone change to recover from jet

lag. Melatonin, available as a dietary supplement, is sometimes used to induce sleep

when traveling. It is more useful when traveling east and may be taken before, during,

or after traveling. It is best taken approximately five to seven hours before the usual

bedtime in the old time zone. Travelers should consult their physicians before using

melatonin. It is not recommended for pregnant or breast-feeding women and children.

| Anatomy , Animal Behavior |

How eye produces tears?

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The lachrymal gland, which is part of the larger lachrymal apparatus, produces tears

that flow over the anterior surface of the eye. Most of this fluid evaporates, but excess

amounts are collected in small ducts in the corner of the eye. Tears lubricate and

cleanse the eye. In addition, tears contain lysozyme, an enzyme that is capable of

destroying certain kinds of bacteria and helps fight eye infections

| Anatomy |

What is the auditory tube and its function?

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The auditory tube (Eustachian tube) connects each middle ear to the throat. This tube

conducts air between the tympanic cavity and the outside of the body by way of the

throat and mouth. It also helps maintain equal air pressure on both sides of the

eardrum, which is necessary for normal hearing. The function of the auditory tube can

be experienced during rapid change in altitude. As a person moves from a high altitude

to a lower one, the air pressure on the outside of the membrane becomes greater and

greater. As a result, the eardrum may be pushed inward, out of its normal position, and

hearing may be impaired. When the air pressure difference is great enough, some air

may force its way up through the auditory tube into the middle ear. This allows the

pressure on both sides of the eardrum to equalize, and the drum moves back to its

regular position. An individual usually hears a popping sound at this time, and normal

hearing is restored. A reverse movement of air occurs when a person moves from a low

altitude to a higher one.

| Anatomy |

What is cerumen?

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Cerumen is an oily, fatty substance produced by the ceruminous glands in the outer

portion of the ear canal. This compound is commonly referred to as ear wax and,

together with hairs in the auditory canal, helps prevent foreign objects from reaching the

delicate eardrum. Dust, dirt, bacteria, fungi, and other foreign dangers to the body all

stick to the wax and do not enter the ear. Ear wax also contains a special enzyme,

lysozyme, which breaks down the cell walls of bacteria. In most individuals, the ear

canal is self-cleansing and there is no need to remove ear wax. However, ear wax may

be impacted due to poor attempts at cleaning the ear. In such cases, the impacted ear

wax should be removed by a healthcare professional.

| Anatomy |

Are body planes important for identifying anatomical structure?

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In order to observe and study the structural arrangement of the internal organs, the

body may be divided and sectioned (or cut) along three fundamental planes. These

planes are the midsagittal (median) plane, the coronal (frontal) plane, and the

transverse (horizontal) plane. The midsagittal plane divides the body lengthwise into

right and left sides. A sagittal section placed off-center divides the body into

asymmetrical right and left sides. The coronal plane divides the body into front (anterior)

and back (posterior) sections. The transverse plane divides the body into upper

(superior) and lower (inferior) sections. It is at right angles to the sagittal and frontal

planes.

| Anatomy |

How is the skin involved in the regulation of body temperature?

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The skin is one of several organ systems participating in maintaining a core

temperature, meaning the temperature near the center of someone’s body.

Temperature sensors in the skin and internal organs monitor core temperature and

transmit signals to the control center located in the hypothalamus, a region of the brain.

When the core temperature falls below its set point, the hypothalamus: 1. Sends more

nerve impulses to blood vessels in the skin that cause the vessels to narrow, which

restricts blood flow to the skin, reducing heat loss. 2. Stimulates the skeletal muscles,

causing brief bursts of muscular contraction, known as shivering, which generates heat.

When the core temperature rises above its set point, the hypothalamus: 1. Sends fewer

nerve impulses to blood vessels in the skin, causing them to dilate, which increases

blood flow to the skin and promotes heat loss. 2. Activates the sweat glands, and when

sweat evaporates off the skin surface it carries a large amount of body heat with it.

| Anatomy , Biochemistry , physiology |

Is all the cartilage in the body the same?

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There are three types of cartilage in the human body: 1) hyaline cartilage; 2) elastic

cartilage; and 3) fibrocartilage. Hyaline cartilage (from the Greek hyalos, meaning

“glass”) is the most common type of cartilage in the body. It has a translucent, pearly,

blue-white appearance resembling glass. Hyaline cartilage provides stiff but flexible

support and reduces friction between bony surfaces. It is found between the tips of the

ribs and the bones of the sternum, at the end of the long bones, at the tip of the nose,

and throughout the respiratory passages. Elastic cartilage is similar to hyaline cartilage

except it is very flexible and resilient. It is ideal for areas that need repeated bending

and stretching. Elastic cartilage forms the external flap of the outer ear and is found in

the auditory canal and epiglottis. Fibrocartilage is often found where hyaline cartilage

meets a ligament or tendon. It is found in the pads of the knees, between the pubic

bones of the pelvis, and between the spinal vertebrae. It prevents bone-to-bone contact.

Cartilage does not contain blood vessels. Oxygen, nutrients, and cellular wastes diffuse

through the selectively permeable matrix. Cartilage transplants are successful because

foreign proteins in the transplanted cells do not have a way to enter the host body’s

circulation and cause an immune response. However, since there are no blood vessels

in cartilage, the healing process is slower than for other tissues


Which types of tissue have the greatest capacity to regenerate?

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Epithelial and connective tissues have the greatest capacity to regenerate. In small

wounds and injuries, the epithelial and connective tissues often heal with normal tissue.

The ability of muscle tissue to regenerate is very limited. Fibrous connective tissue often

replaces damaged muscle tissue. As a consequence, the organ involved loses all or

part of its ability to function. Nerve tissue has even less capacity to regenerate.

Although neurons outside the brain and spinal cord sometimes regenerate at a very

slow pace, most brain and spinal cord injuries result in permanent damage.


Are there differences between the male and female skeletons?

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Several general differences exist between the male and female skeletons. The male

skeleton is generally larger and heavier than the female skeleton. The bones of the skull

are generally more graceful and less angular in the female skeleton. A female also has

a wider, shorter breastbone and slimmer wrists. There are significant differences

between the pelvis of a female and a male, which are related to pregnancy and

childbirth. The female pelvis is wider and shallower than the male pelvis. Females have

an enlarged pelvic outlet and a wider, more circular pelvic inlet. The angle between the

pubic bones is much sharper in males, resulting in a more circular, narrower, almost

heart-shaped pelvis

| Anatomy , Gynacology |

What is rigor mortis?

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Dead bodies are at first limp. Several hours after death, the skeletal muscles undergo a

partial contraction that fixes the joints. This condition, known as rigor mortis, may

continue for 72 hours or more. When neurons signal living muscle fibers to contract,

they do so with a neurotransmitter that is received at the surface of the muscle fiber.

The signal makes the fiber open calcium ion channels, and it is the calcium that causes

the contraction. The muscle then removes the calcium in two ways: it stores some in its

mitochondria, and it pumps out the rest. When a body dies, stored calcium leaks and

calcium pumps no longer function. The excess calcium causes the actin and myosin

filaments of the muscle fibers to remain linked, stiffening the whole body until the

muscles begin to decompose.


How do bones grow?

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Bones form and develop through a process called ossification. There are two types of ossification: intramembranous ossification and endochondral ossification. Intramembranous ossification is the formation of bone directly on or within the fibrous connective tissue. Examples of bone formed through intramembranous ossification are the flat bones of the skull, mandible (lower jaw), and clavicle (collarbone). Endochondral ossification, from the Greek endo, meaning “within,” and khondros, meaning “cartilage,” is the transformation of the cartilage model into bone. Cartilage cells in the epiphyseal plate grow and move into the metaphysis where they are reabsorbed and replaced by bone tissue. Examples of bone formed through endochondral ossification are the long bones, such as the femur and humerus.

| Anatomy , Biochemistry |

Which structures of the body have more bones for their size than any other part of the body?

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The wrist and the hand have more bones in them for their size than any other part of the body. There are 8 carpals in the wrist between the forearm and the palm of the hand; 5 metacarpal bones that form the palm of the hand between the wrist, thumb, and fingers; and 14 phalanges or finger bones. The presence of many small bones in the wrist and hand with the many movable joints between them makes the human hand highly maneuverable and mobile.

| Anatomy |

Why is there a “popping” sound when you crack your knuckles, and is it dangerous to crack them?

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A number of reasons have been given for the characteristic “popping” sound associated with someone cracking their knuckles. One reason is that when a joint is contracted, small ligaments or muscles may pull tight and snap across the bony protuberances of the joint. Another possibility is that when the joint is pulled apart, air can pop out from between the bones, creating a vacuum that produces a popping sound. A third reason, discovered by British scientists in 1971, is that when the pressure of the synovial fluid is reduced by the slow articulation of a joint tiny gas bubbles in the fluid may burst, producing the popping sound. Research has not shown any connection between knuckle cracking and arthritis. One study found that knuckle cracking may be the cause of soft tissue damage to the joint capsule and a decrease in grip strength. The rapid, repeated stretching of the ligaments surrounding the joint is most likely the cause of damage to the soft tissue. Some researchers believe that since the bones of the hand are not fully ossified until approximately age 18, children and teenager who crack their knuckles may deform and enlarge the knuckle bones. However, most researchers believe knuckle cracking does not cause serious joint damage.

| Anatomy , Psychology |

Why is a woman’s voice usually higher than a man’s voice?

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| Anatomy , Facts |

Why is it dangerous to talk while eating?

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If a person talks while eating, food may be inhaled into the lungs. Normally, after food is

swallowed, it passes into the pharynx and then into the esophagus. Food is prevented

from entering the larynx (the passageway to the lungs) by the epiglottis, a spade-

shaped cartilage flap that covers the pharynx. If food does enter the larynx, a cough

reflex is usually initiated, although food may lodge in the larynx, causing a blockage of

the airway.

| Anatomy , Facts |

Distinguish among the terms stimulus, sensation, and perception

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A stimulus is an energy source (chemical, pressure, light wave, etc.) that activates a

receptor cell (specialized nerve cell) to transmit a nerve impulse, or sensation. If the

sensation arrives in the conscious part of the brain, the cerebral cortex, a perception

occurs. Perception is awareness of the stimulus. Pricking one’s finger, for example, is a

stimulus that activates many receptor cells to send nerve impulses

to the brain. Once these sensations reach the cerebral cortex, a person perceives

(feels) pain.

Molecular Biology

What are the main causes of Mutation?

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Some mutations occur randomly and spontaneously during the process of mitosis or

meiosis. Other mutations are caused by mutagenic agents, which are environmental or

man-made factors that can increase the frequency of mutation. Environmental factors

such as ultraviolet rays of the sun can cause changes in DNA that can lead to skin

cancer. Cosmic rays from space that penetrate the earth’s ozone layer are also a cause

of mutation. Ionizing radiation such as X-rays, gamma rays, and nuclear radiation

produce free radicals (atoms with unpaired electrons) in the cell that can cause breaks

in the DNA molecule. Carcinogens are chemical mutagens that cause gene mutations,

which can result in cancer. A few examples of carcinogens are asbestos, benzene,

some food dyes, and PCBs.

| Molecular Biology |

What is an example of gene control?

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An elegant example of gene control in bacteria is the operon system. A cluster of genes

that is responsible for synthesizing a particular protein is called an operon. This cluster

of genes typically includes a promoter region, an operator gene, a regulatory gene, and

a number of structural genes that actually encode the protein. Operon systems can be

inducible (meaning they are normally “off”) or repressible (meaning they are normally

“on”).

| Genetics , Molecular Biology |

Is a gene the same as a DNA molecule?

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Genes are the units of heredity. A gene is a segment or section of a DNA molecule.

This segment of DNA provides a genetic code for the synthesis of proteins. The nucleic

acid language of the gene is written as a sequence of bases on the DNA molecule.

Such a sequence might read G- C- T- T- A- C- C- G- A- T- T. . . . This is the molecular

“language” that will ultimately specify an amino acid sequence in a protein.


Do all molecules of DNA have the same amounts of nitrogenous bases?

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The number and sequence of nitrogenous bases in the DNA molecule are key elements

in variations that are found in chromosomes. Different organisms have different

numbers of the four bases, and the sequence varies in countless ways. In all cases,

however, adenine and thymine always stand opposite each other, and cytosine and

guanine oppose one another. This means that the percentage of adenine and thymine

will always be the same, as will the percentage of cytosine and guanine.


How sex occurs in bacteria?

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The occurrence of sex in bacteria was first described by Joshua Lederberg and Edward

Tatum in 1946 (Nature, volume 158, page 558), who were studying mixed cultures of E.

coli strains with various nutritional mutations. The mutant strains differed from the wild

type strains in lacking the ability to synthesize growth factors such as amino acids and

vitamins, similar to the strains in the present problem.

In one experiment, two triple mutants of E. coli, one requiring threonine, leucine, and

thiamine, and the second requiring biotin, phenylalanine, and cystine were grown in

mixed cultures. At very low frequency, recombinant strains with no growth-factor

requirement were obtained. They ruled out spontaneous mutations and transformation

by the culture medium as the source of recombinant strains. In the words of Lederberg

and Tatum, "These experiments imply the occurrence of a sexual process in the

bacterium Escherichia coli."

| bacteriology , Molecular Biology |

What are the features of hnRNA?

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Heterogeneous nuclear RNA (hnRNA) - The primary precursor mRNA transcript made

in the eukaryotic nucleus are called "hnRNA," an abbreviation for "heterogeneous

nuclear RNA. Features are as follows:

Introns: Since many eukaryotic nuclear genes are interrupted by introns, RNA

transcripts of intron-containing genes have intronic RNA sequences.

Poly A tails at the 3'-end: Poly A tails added to the 3'-end of most, but not all hnRNAs

during nuclear RNA processing. These tails are retained in the processed mRNA.

5'-Cap structure: A modified GTP is covalently attached to the 5'-end of most precursors

to mRNA. This cap structure is also retained in the processed mRNA.

Base Composition and relation to template strand: RNA is synthesized from a DNA

template. The sequence of the RNA is complementary to the DNA template strand, and

opposite in polarity. C and T in the DNA template are transcribed by RNA polymerase

as G and A in the hnRNA, respectively. A and G in the DNA template are transcribed as

U and C in hnRNA. Thus hnRNA and mRNA are sequences of A, G, C and U's.


How DNA-RNA hybridization occurs

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Both DNA and RNA are able to form hybrids in solution with other DNA or RNA

molecules that have complementary base pairing. Double-stranded DNA can be

"denatured" by heating to high temperature. If the resulting single-stranded DNAs are

slowly cooled, the separated DNA strands can reanneal to reform the DNA duplex.

Notice that A pairs with T and G pairs with C when a DNA strand hybridizes with

another DNA strand. An RNA molecule can also form a base-paired DNA-RNA duplex

molecule with a DNA that has complementary base pairing. The most common source

of DNA complementary to an mRNA is the DNA coding strand that was the template for

synthesis of the RNA. In DNA-RNA hybrid formation, G base pairs with C, A of the RNA

pairs with T of the DNA, and U or the RNA pairs with A of the DNA.


What is self-catalytic RNAs?

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Ribozymes - The term "ribozyme" was originally suggested by Thomas R. Cech, Nobel

Prize winning biochemist, who first discovered this class of RNA molecules. A ribozyme

is an RNA molecule that can catalyze a biochemical reaction. Prior to the discovery of

ribozymes, it was generally assumed that protein enzymes were the only class of

biological catalysts. Cech's discovery was truly revolutionary in upsetting this dogma.

The first ribozymes discovered were introns that could catalyze their own splicing, i.e. a

special type of intron within a pre-RNA molecule was found to catalyze all steps needed

for intron removal and joining of the exons together at the biologically correct site.

Ribozymes with other types of biological activity have since been discovered. One

intriguing potential ribozyme is the peptidyl transferase activity of the ribosome. Many

believe that peptide bond formation is catalyzed by the 23S ribosomal RNA, a potential

ribozyme, rather than ribosomal proteins.


How much DNA is in a typical human cell?

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If the DNA (deoxyribonucleic acid) molecules in a single human cell were stretched out

and laid end to end they would measure approximately 6.5 feet (2 meters). The average

human body contains 10 to 20 billion miles (16 to 32 billion kilometers) of DNA

distributed among trillions of cells. If the total DNA in all the cells from one human were

unraveled, it would stretch to the sun and back more than 500 times.


What are the stages of mitosis?

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Mitosis involves the replication of DNA and its separation into two new daughter cells.

while only four phases of mitosis are often listed. the entire process is actually

comprised

of six phases:

• Interphase: Involves extensive preparation for the division process.

• Prophase: The condensation of chromosomes; the nuclear membrane disappears;

formation of the spindle apparatus; chromosomes attach to spindle fibers.

• Metaphase: Chromosomes, attached by spindle fibers. align along the mid-line of a

cell.

• Anaphase: The centromere splits and chromatin move apart.

• Telophase: The nuclear membrane reforms around newly divided chromosomes.

• Cytokinesis: The division of cytoplasm, cell membranes, and organelles occur. In

plants. a new cell wall forms.

| cell biology , cell signaling , cell structure , Molecular Biology |

What is green fluorescent protein (GFP) ?

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Green fluorescent protein is a protein found in a luminescent jellyfish (Aquorea victoria)

that lives in the cold waters of the northern Pacific. Bioluminescence is the production of

light by living organisms. These jellyfish contain two proteins: a bioluminescent protein

called aequorin that emits blue light, and an accessory green fluorescent protein (GFP).

However, what we actually see when the jellyfish fluoresces is the conversion of the

blue light emitted by aequorin to a green Iight-a metabolic reaction facilitated by the

GFP. Since GFP is simply a protein, it is often used both as a marker for gene transfer

and for localization of proteins. There are a variety of green fluorescent proteins that

can glow different colors.

| Biochemistry , Molecular Biology , Protein |

What is genetic engineering?

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Genetic engineering, also popularly known as molecular cloning or gene cloning, is the

artificial recombination of nucleic acid molecules in a test tube; their insertion into a

virus, bacterial plasmid, or other vector system; and the subsequent incorporation of the

chimeric molecules into a host organism in which they are capable of continued

propagation. The construction of such molecules has also been termed gene

manipulation because it usually involves the production of novel genetic combinations

by biochemical means. Genetic engineering techniques include cell fusion and the use

of recombinant DNA or gene-splicing. In cell fusion the tough outer membranes of

sperm and egg cells are removed by enzymes, and then the fragile cells are mixed and

combined with the aid of chemicals or viruses. The result may be the creation of a new

life form from two species (a chimera). Recombinant DNA techniques transfer a specific

genetic activity from one organism to the next through the use of bacterial plasmids

(small circular pieces of DNA lying outside the main bacterial chromosome) and

enzymes, such as restriction endonucleases (which cut the DNA strands); reverse

transcriptase (which makes a DNA strand from an RNA strand); DNA ligase (which joins

DNA strands together); and Taq polymerase (which can make a double-strand DNA

molecule from a single-strand "primer" molecule). The recombinant DNA process

begins with the isolation and fragmentation of suitable DNA strands. After these

fragments are combined with vectors, they are carried into bacterial cells, where the

DNA fragments are "spliced" on to plasmid DNA that has been opened up. These hybrid

plasmids are then mixed with host cells to form transformed cells. Since only some of

the transformed cells will exhibit the desired characteristic or gene activity, the

transformed cells are separated and grown individually in cultures. This methodology

has been successful in producing large quantities of hormones (such as insulin) for the

biotechnology industry. However, it is more difficult to transform animal and plant cells.

Yet the technique exists to make plants resistant to diseases and to make animals grow

larger. Because genetic engineering interferes with the processes of heredity and can

alter the genetic structure of our own species, there is much concern over the ethical

ramifications of such power, as well as the possible health and ecological

consequences of the creation of these bacterial forms.

Some applications of genetic engineering in various fields are:

• Agriculture: Crops having larger yields, disease- and drought-resistancy; bacterial

sprays to prevent crop damage from freezing temperatures; and livestock improvement

through changes in animal traits.

• Industry: Use of bacteria to convert old newspaper and wood chips into sugar; oil- and

toxin-absorbing bacteria for oil spill or toxic waste cleanups; and yeasts to accelerate

wine fermentation.

• Medicine: Alteration of human genes to eliminate disease (experimental stage); faster

and more economical production of vital human substances to alleviate deficiency and

disease symptoms (but not to cure them); substances include insulin, interferon (cancer

therapy), vitamins, human growth hormone ADA, antibodies, vaccines, and antibiotics.

• Research: Modification of gene structure in medical research, especially cancer

research.

• Food processing: Rennin (enzyme) in cheese aging.

| cell biology , Genetics , Molecular Biology |

How the DNA nanoarchitecturing works?

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DNA nanoarchitectures constructs that can be self-assembled from branched DNA

molecules. Their components may be simple branched species or more complex

structural motifs. Simple branched DNA junctions have been produced that contain 3–

12 double helices flanking a branch point. The species can be assembled and/ or

ligated into DNA stick polyhedra, where the edges are DNA double helices and the

vertices correspond to the branch points of the junctions. The first such molecule was a

DNA molecule with the connectivity of a cube. Other polyhedra produced to date include

a tetrahedron, an octahedron and a truncated octahedron. Branched junctions are

somewhat floppy, so only the branching and linking topologies of polyhedral are well

defined unless all the faces are triangles. Other individual objects that have been built

are topological targets, such as knots and Borromean rings. DNA is an ideal species to

use as a topological building block because a half-turn of DNA is equivalent to a node,

which is the fundamental topological feature of a knot or a catenane. The DNA double-

crossover (DX) molecule is another key element in DNA nanoarchitectures. This motif

consists of two helices joined twice by strands that connect them, leading to parallel

helix axes; the connection points are separated typically by Two-dimensional DNA

lattice. one and two double helical turns. Each of the connection points is a four-arm

junction, so the motif can be described as two four-arm junctions joined twice to each

other at adjacent arms. These are robust motifs, usually three to six double helical turns

in length and their structures can be reliably predicted. This system can be extended,

leading to molecules containing three or more helices joined laterally. Although most

often built to be roughly planar motifs, angles can be varied between pairs of helices,

using the helicity of DNA, e.g. a six-helix cyclic motif has been reported that

approximates a hexagonal tube (→DNA nanotubes). DX molecules and their relatives

can be exploited as tiles to produce two-dimensional crystalline arrangements by self-

assembly (→DNA self-assembly). An extra motif can be included in these tiles, visible

when the crystal is viewed in an atomic force microscope. The accompanying picture

shows how arrangements of two 16 × 4 nm tiles produce 32-nm stripes (top) or four tiles

produce 64-nm stripes (bottom). In addition to periodic arrangements, aperiodic patterns

can also be generated algorithmically. Single-stranded bacteriophages have been used

to produce greatly extended versions of the parallel DNA motif, capable of yielding

highly elaborate patterns, in a method called DNA origami. This is done by using the

bacteriophage genome (several thousand nucleotides) as a template to which a large

number of “staple strands” are added to fold the genome into a specific shape, including

holes in the middle; the addition of strands containing extra domains enable the

generation of further features. Smiley faces and a map of the western hemisphere are

examples of patterns generated by this method.

| Molecular Biology , Nanobiotechnology |

What is Barr body Genes?

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Located inside the nuclear envelope, it is a densely staining object that is an inactivated

X chromosome in female mammalian cells. Most Barr body genes are not expressed.

They are reactivated in gonadal cells that undergo meiosis to form gametes. Female

mammals are a mosaic of two types of cells, those with an active maternal X and those

with an active paternal X. Which of the two Xs will be inactivated is determined

randomly in embryonic cells. After an X is inactivated, all mitotic descendants will have

the same inactive X. As a consequence, if a female is heterozygous for a sex-linked

trait, about half of her cells will express one allele and the other cells well express the

alternate allele. Examples of this type of mosaicism are coloration in calico cats and

normal sweat gland development in humans. A woman who is heterozygous for this trait

has patches of normal skin and patches of skin lacking sweat glands. X chromosome

inactivation is associated with DNA methylation. Methyl groups (-CH3) attach to

cytosine, one of DNA’s nitrogenous bases. Barr bodies are highly methylated compared

to actively transcribed DNA.

What determines which of the two X chromosomes will be methylated? – A recently

discovered gene, XIST is active only on the Barr body. The product of the XIST gene,

X-inactive specific transcript, is an RNA; multiple copies of XIST attach to the X

chromosome inactivating it.


How Genes can be exchanged between chromatids?

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When two homologous chromosomes physically exchange corresponding segments

during prophase I of meiosis, geneticists call it crossing over. Recombinations occur at

chiasmata during pachytene of meiosis-I. If just a few exchanges occur, genes that are

closer together tend to stay together. The farther apart on the same chromosome genes

are, the more likely they will separate during recombination. The two extremes are

independent assortment and complete or absolute linkage. The progeny resulting from

crossing over appear in repeatable proportions, called the recombinant frequency.

Greater recombination frequencies are observed for genes that are farther apart on the

chromosomes because a chiasma is more likely to cut between genes that are far apart

than genes that are closer together.


Can we make artificial cells?

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Research in progress at the National Aeronautical and Space Administration (NASA) is

focused on artificial cells as a means to deliver medicine in outer space; these cells are

able to withstand dehydration and thus can be safely stored for long periods. Artificial

cells are made of a polymer that acts like a cell membrane, but the polymer is stronger

and more manageable than real membranes. These polymers are called polymersomes

and can be made to cross-link with other polymers. Researchers feel that many different

kinds of molecules can be encapsulated within these polymersomes and then delivered

to specific target organs. An example would be an artificial blood cell that not only

delivers oxygen but also medication as it travels through the body.


How DNA Repair can happen?

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A. DNA damage caused by ultraviolet light: 1. cyclobutane-type pyrimidine dimer is

the major photoproduct formed 2. a second product, the 6-4 photoproduct, is formed in

about 10 % of UV induced pyrimidine dimmers 3. the cyclobutane type dimer can be

reversed by a process called photoreactivation (a) this is carried out by an enzyme

called DNA photolyase (photoreactivating enzyme) (b) importance of the photolyase

enzyme in humans is questionable 4. DNA photoproducts can also be repaired by

excision repair

B. Spontaneous deamination of cytosine: 1. deamination of cytosine is common and

results in the conversion of cytosine to uracil 2. can be repaired by excision repair

process (i) uracil-DNA glycosylase hydrolyzes N-glycosidic bond to remove uracil base

(ii) AP endonuclease removes deoxyribose-phosphate (iii) gap is extended by

exonuclease (iv) gap is filled by DNA polymerase I and nick is sealed by DNA ligase

C. Depurination: Pathway is similar to that above except that excision repair begins

with AP endonuclease

D. DNA damaged by alkylating agents: 1. Some simple alkylating agents 2. examples

of products of alkylating agents 3. many of these products can be repaired by excision

repair that is initiated by specific glycosylases 4. some damage resulting from

methylation can be reversed by methyltransferases (a) O6-methylguanine-DNA

methyltransferase

E. Mismatch repair: 1. mismatches can occur when DNA polymerase inserts the wrong

nucleotide during replication 2. mismatch repair is “coupled” to replication

F. Recombinational repair: 1. occurs during DNA replication 2. major steps: (a) DNA

polymerase skips over damaged DNA leaving a gap opposite the lesion (b) the

undamaged parental strand recombines into the gap (this is facilitated by recA protein in

E. coli) (c) the new gap in the parental strand is filled by DNA polymerase and ligase

G. Genetic Defects in DNA repair and human disease: 1. Xeroderma pigmentosum

is an inherited disease that is characterized by severe photosensitivity and a very high

incidence of skin cancers. It is due to defective excision repair. 2. Bloom’s syndrome. 3.

Cockayne’s syndrome 4. Fanconi’s anemia 5. Ataxia telangiectasia

| Biochemistry , Molecular Biology |

Why does thymine replace uracil in DNA?

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First, some clarification. As you already know, the difference between RNA and DNA is

the existence of a hydroxyl (-OH) group on the 2' carbon of the ribose sugar in the

backbone. The removal of 2' hydroxyl groups from DNA does not occur after the DNA

has been synthesized, but rather the 2' hydroxyl groups are removed from the

nucleotides before they are incorporated into the DNA. During nucleotide synthesis, a

portion of the nucleotide monophosphates (NMP's) are dehydroxylated to 2'-deoxy-

nucleotide monophosphates (dNMP's). This means that GMP, AMP, CMP, and UMP

are converted into dGMP, dAMP, dCMP, and dUMP, respectively. However, before

being incorporated into the chromosomes, another modification, using folic acid as a

catalyst, methylates the uracil in dUMP to form a thymine making it dTMP. After further

phosphorylation, dGTP, dATP, dCTP, and dTTP can be used as the building blocks to

construct DNA.

The important thing to notice is that while uracil exists as both uridine (U) and deoxy-

uridine (dU), thymine only exists as deoxy-thymidine (dT). So the question becomes:

Why do cells go to the trouble of methylating uracil to thymine before it can be used in

DNA?

The answer is: methylation protects the DNA. Beside using dT instead of dU, most

organisms also use various enzymes to modify DNA after it has been synthesized. Two

such enzymes, dam and dcm methylate adenines and cytosines, respectively, along the

entire DNA strand. This methylation makes the DNA unrecognizable to many Nucleases

(enzymes which break down DNA and RNA), so that it cannot be easily attacked by

invaders, like viruses or certain bacteria. Obviously, methylating the nucleotides before

they are incorporated ensures that the entire strand of DNA is protected. Thymine also

protects the DNA in another way. If you look at the components of nucleic acids,

phosphates, sugars, and bases, you see that they are all very hydrophilic (water

soluble). Obviously, adding a hydrophobic (water insoluble) methyl group to part of the

DNA is going to change the characteristics of the molecule. The major effect is that the

methyl group will be repelled by the rest of the DNA, moving it to a fixed position in the

major groove of the helix. This solves an important problem with uracil - though it

prefers adenine, uracil can base-pair with almost any other base, including itself,

depending on how it situates itself in the helix. By tacking it down to a single

conformation, the methyl group restricts uracil (thymine) to pairing only with adenine.

This greatly improves the efficiency of DNA replication, by reducing the rate of

mismatches, and thus mutations.

To sum up: the replacement of thymine for uracil in DNA protects the DNA from attack

and maintains the fidelity of DNA replication.


Suppose the restriction endonuclease HindIII cuts a 6.0 kb linear piece of DNAinto two fragments; an 800 bp fragment and a 5200 bp fragment.....

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QuestionSuppose the restriction endonuclease HindIII cuts a 6.0 kb linear piece of

DNAinto two fragments; an 800 bp fragment and a 5200 bp fragment. NarI cuts the

DNA also into two fragments; fragments 1200 and 4800 bp long. Relative to the HindIII

cut site, there are two possible ways in which NarI could have cut the DNA. How can

you determine the correct cleavage site for NarI with respect to HindIII?

Answer

To determine this, one must subject the DNA to a double digest in which both the

enzymes are allowed to cut the DNA at the same time. When the double digest is

allowed to take place, if the three fragments that appear upon electrophoresis of the

restricted DNAare 400, 800, and 4800 bp, then the only possible way in which the data

can be interpreted is with the 1200 bp NarI fragment containing the HindIII recognition

site 800 bp from the end of the linear piece of DNA. If the 4800 bp NarI fragment

contained the cut site, you would visualize fragments of sizes 800, 1200, and 4000 bp

after electrophoresing the doubly digested DNA.


Why is the concept of a single gene as the ultimate unit of inheritance inadequate to provide a unitary explanation for protein synthesis?

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Question:

Why is the concept of a single gene as the ultimate unit of inheritance inadequate to

provide a unitary explanation for protein synthesis, recombination, and mutation?

Answer:

The primary function of the gene is to code for a protein product. Sufficient DNA must

be present to account for each of the amino acids making up the primary structure of

the protein. It is this length of DNA that is designated the cistron. This is the basic unit of

function of the gene; however, there are units of function below this primary level. A

mutation involves a change in the original message contained within the cistron. Such a

change may lead to the manufacture of no protein or an altered protein. Since, in some

cases, change in even a single base may produce a mutation, only tiny lengths of DNA

may represent a unit for mutation—the muton. The cistron may thus contain hundreds

of mutons. The minimum length of DNA participating in exchanges of genetic

information is not clearly apparent. Exchanges of relatively few bases between

chromosomes would probably not result in the mutual transfer of intact message

material. The recon, the unit involved in recombination, may be only slightly shorter than

the full cistron.

| Molecular Biology

What are introns, and how do they affect the processing of genetic information?

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Introns, a feature of eukaryotic DNA, are intervening stretches of DNA lying between the

exons. The exons represent message material that actually gets translated into protein,

whereas the introns must eventually be excised from the final mRNA product. Initially,

both introns and exons are coded into an mRNA transcript. The existence of introns and

exons was demonstrated when it was discovered that only about one-third of the

primary transcript of DNA was used to make protein. In a highly complicated process,

the intron regions are removed from the rough primary transcript on the DNA template

to produce a secondary, mature mRNA that codes only for the exons. It is now clear

that initiator and terminator signals must mark the beginning and end of each intron

within a gene.

Despite the fact that the intron is not directly involved in shaping the final protein

product, it appears to be essential to the synthesis of a functional mRNA. The process

of excising the intron regions involves the participation of RNA as an enzyme. This

catalytic RNA is part of a protein-RNA particle known as the small nuclear

ribonucleoprotein particle.


The development of genetic engineering has raised various concerns, moral and scientific. What might some of these be?

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In many bacteria, the plasmids used in recombinant studies contain the gene conferring

resistance to antibiotics.It was feared, during early attempts to effect DNA

transplantation, that bacteria would be created that would be resistant to all known

antibiotics. The possibility of an uncontrolled plague that would sweep through the

human population was only one of many concerns that arose from consideration of the

consequences of tinkering with thegenetic apparatus.

Cloning also presents scientific and ethical questions. Since the cloning technique does

not involve the usual sexual process for recombining genetic material, it short-circuits a

mechanism for providing variability, which in turn deprives the organism of adaptive

potential and thus leaves it more vulnerable to selection pressures. Questions also have

arisen about the legal status of a possible human clone, since it would be a genetic

replica of one individual but would be born to a woman who has provided a foster womb

without making a genetic contribution to the clone

Questions exist about who the parents of the clone would be, what family relationships

the cloned person would have,etc. These considerations involve the legal and religious

communities as well as biologists. In some countries, special panels have been set up

to deal with the ethical and biological issues involved in genetic engineering.


What features of the structure of mRNA enable its interaction with the 30S subunit?

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Toward the 5′ end of mRNA there is a region of ~20 nucleotides prior to the initiation

codon AUG. This leader region contains a purine-rich sequence that is responsible for

the interaction of the mRNA with the 30S subunit. It is known as the Shine-Dalgarno

sequence (after John Shine and Lynn Dalgarno, the Australians who made the

discovery); it can

bind to a complementary sequence at the 3′ end of the 16S rRNA to orient the 30S

subunit appropriately for initiation.

The Shine-Dalgarno sequence distinguishes the initiating AUG, which also determines

the reading frame, from an AUG that encodes an internal methionine. Other sequences

in the leader region are possibly involved in the overall process of initiation of

translation, which also involves the binding of the appropriately charged methionyl-tRNA

opposite the AUG codon.


What characteristics of DNA polymerase III make it an ideal enzyme for replicating the whole genome?

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The key features of DNA polymerase III are its catalytic potency, its fidelity, and its

processivity. It is able to catalyze the addition of ~103 bases per second, compared to

only about 10 per second for DNA polymerase I,with an error frequency of about 1:104–

105. One of the unique features of DNA polymerase III is its ability to continuously

synthesize very long (thousands of bases) stretches of DNA, unlike DNA polymerase I.

This is a consequence of its processivity; the β2 sliding clamps ensure that it remains

bound to the template strand DNA.

In contrast, DNA polymerase I, without a sliding clamp, is much more likely to dissociate

from the template strand after synthesis of short (tens of bases) stretches of DNA.


How do we study what function(s) a particular gene has in a cell?

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One of the most informative ways to investigate the function of a gene is to determine

its effect in vivo, by artificially introducing DNA into the cells of an organism. Such DNA

is called a transgene (transferred gene), and such organisms are known as transgenic.

Transgenes can be used to investigate gene function either by introducing a new gene,

new regulatory regions, or a mutated version of an endogenous gene, or by inactivating

an endogenous gene. A new or enhanced gene activity conferred by a transgene is

known as a gain-offunction mutation, whereas a loss-of-function mutation results in

reduced or abolished gene function.

Common transgenic animals, in order of complexity, include baker’s yeast

(Saccharomyces cerevisiae), the nematode worm (Caenorhabditis elegans), the fruit fly

(Drosophila melanogaster), and the mouse (Mus musculus). Evolutionary conservation

means that their genes share a degree of homology with human genes, so that

discoveries about function made with these organisms frequently apply to humans.

While similar genetic manipulations can be performed in vitro using cell culture,

transgenic organisms provide more physiologically relevant data, resulting from the

interaction of gene products with all components of an intact organism. Transgenic

organisms therefore provide models to explore gene function, gene control, and human

diseases


How is the production of a tissue-specific protein restricted to a particular tissue when the gene is present in the nucleus of all cells?

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Most of the control of tissue-specific gene expression occurs at the level of transcription;

this is achieved with tissuespecific transcription factors. E.g., all the genes that are to be

expressed in erythroid cells (such as globins, spectrin, and the erythropoietin receptor)

have the site -AGATA- in their promoters. This promoter is only active when bound by a

transcription factor, called GATA-1, which is present only in erythroid cells.


RNA polymerase inhibitors - Why is this so?

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Question

The bacterial RNA polymerase inhibitors rifampicin and streptolydigin each bind to the

same subunitof the enzyme, but their overall effect on the activity of the enzyme is

different. Why is this so?

Answer

Each of these inhibitors binds exclusively to the β-subunit of RNA polymerase. This

subunit is involved in both initiation and elongation of RNA chain growth. Rifampicin

binds to the subunit in such a way to affect only the initiation step; it has no effect on

elongation. Streptolydigin, on the other hand, binds in a manner that blocks both

activities.

Immunology What is the life span of antibodies in body circulation?

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Antibodies, as noted, are protein molecules. They will either leave the body in

secretions or be broken down by enzymes that degrade proteins in the body. The

average life span of most antibody molecules is roughly a few weeks. Continued

antigen stimulation is necessary to continue the antibody response, and as the antigen

disappears, the stimulation disappears. The antibodies produced as a result of the initial

stimulation remain in the bloodstream for a long period of time, with about half the

quantity disappearing after a few weeks and half the remaining disappearing after

another few weeks, and so forth. In many cases, the antibody level is sufficient to

sustain an individual for the remainder of his or her life, especially after recovery

from disease.

| Immunology |

What is the function of the helper T cell?

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The helper T cells assist the immune process by helping other cells in the immune

system to achieve an efficient immune response. In antibody- mediated immunity, the

helper T cell helps recognize the MHC molecule and the epitope on the antigen-

presenting cell surface, and it assists the interaction between the B cell and the

macrophage. Thus, the helper T cell is involved in antibody- mediated immunity. In

addition, helper T cells are involved in the activation of cytotoxic T cells. These cells are

critical to both antibody mediated and cell- mediated immunity.

| Immunology |

Are any immunodeficiency diseases related to the stem cells in humans?

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Both the B and T cells are derived ultimately from cells in the bone marrow called stem

cells. When the stem cells are missing or defective, the individual fails to form B cells

and T cells. This condition is known as severe combined immunodeficiency disease

(SCID). Confinement to a sterilized plastic bubble used to be required for these

individuals because they are unable to mount immune defenses against any antigens.

The typical treatment option for SCID is a bone marrow transplant.

| Immunology |

How does blood circulate in the fetus?

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Fetal circulation differs from circulation after birth because the lungs of the fetus are

nonfunctional. Therefore, blood circulation essentially bypasses the lungs in the fetus.

The umbilical vein carries oxygenated blood from the placenta to the fetus. About half of

the blood from the umbilical vein enters the liver, while the rest of the blood bypasses

the liver and enters the ductus venosus. The ductus venosus joins the inferior vena

cava. Blood enters the right atrium of the heart and then flows through the foramen

ovale to the left atrium. Blood then passes into the left ventricle (lower portion of the

heart) and then to the aorta. From the aorta, blood is sent to the head and upper

extremities. It returns to the right atrium of the heart through the superior vena cava.

Some blood stays in the pulmonary trunk to reach the developing lung tissues.

| Biochemistry , Gynacology , Immunology |

What are the benefits of artificial blood?

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Artificial blood is a blood substitute that can be used to provide fluid volume and carry

oxygen in the vessels. Two characteristics that a blood substitute should have is that it

should be thinner than real blood and it should have a low affinity for oxygen so that

oxygen can be delivered easily. The benefits of artificial blood are that it lessens the

demand for human blood supplies and it can be given immediately without triggering a

rejection in cases of massive blood loss. Synthetic chemical compounds called

perfluorocarbons are currently being studied as a substitute for red blood cells. For such

a substitute to be acceptable, it needs to be: 1) able to carry oxygen and release it to

tissues;

2) nontoxic; 3) storable; 4) able to function for varying periods of time in the human

body; and, 5) immune-response resistant.

| Immunology |

Why are red blood cells disc shaped ?

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Red blood cells are perhaps the most specialized cells in the human body. They are a

biconcave (donut) shape with a thin central disc. This shape is important because the

disc increases the surface-area-to-volume ratio for faster exchange of gases and it

allows red blood cells to stack, one on another, as they flow through very narrow

vessels. Also, since some capillaries are as narrow as 0.00015748 inches (0.004

millimeters), red blood cells can literally squeeze through narrow vessels by changing

shape.

| Blood chemistry , Immunology |

How Monoclonal Antibody differs from Polyclonal Antibody?

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If an antigen is injected into an animal, a number of antibody-producing cells will bind

that antigen albeit with varying degrees of affinity, and so the antibody which appears in

the bloodstream will have arisen from several clones of cells, that is it will be a

polyclonal antibody. Different antibody molecules in a preparation of polyclonal antibody

will bind to different parts of the macromolecular antigen and will do so with different

binding affinities. The binding region recognized by any one antibody molecule is called

an epitope. Most antibodies recognize particular surface structures in a protein rather

than specific amino acid sequences (i.e. the epitopes are defined by the conformation of

the protein antigen). A preparation of polyclonal antibodies will bind to many epitopes on

the protein antigen. Whereas, Monoclonal antibodies are single clone of antibody-

producing cells could be isolated, then all of the antibody produced from that clone

would be identical; all antibody molecules in such a monoclonal antibody preparation

would bind to the same antigen epitope. The problem is that if an individual antibody-

producing cell is isolated and grown in culture, its descendants have a limited lifespan

that severely limits their use for the routine preparation of monoclonal antibodies.

Monoclonal antibodies produced using this technology are now common tools in

research because of their very high specificity. For example, they can be used to locate

particular molecules within cells or particular amino acid sequences within proteins. If

they are first bound to an insoluble matrix, they are also extremely useful for binding to

and hence purifying the particular molecule from crude cell extracts or fractions .They

are also increasingly of use in medicine, both for diagnosis and as therapeutic tools, for

example to inactivate bacterial toxins and to treat certain forms of cancer.

| Biochemistry , Immunology |

What is Complement system in Immunology?

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When the recognition function of the humoral immune system has been carried out by

the production of specific antibodies and their binding to foreign antigens, destruction of

the invading pathogen is the next step. One main defense pathway is the complement

system which is activated by antibodies bound to the invading microorganism and

eventually causes it to lyse by punching holes in its plasma membrane. The

complement system consists of about 20 interacting soluble proteins that circulate in the

blood and extracellular fluid. Immunoglobulin molecules bound to the surface of the

microorganisms activate C1, the first component of the complement pathway. The

activation occurs through the Fc portion of the bound antibody. Only bound antibody

can activate complement, soluble antibody not bound to an antigen has no such effect.

The early components of the complement pathway, including C1, are proteases that

activate their substrate by limited cleavage. Activated C1 now activates several

molecules of the next component by proteolysis, each of which activates several

molecules of the next component by proteolysis, and so on. Therefore, the early steps

in complement activation consist of a proteolytic cascade in which more and more

molecules are activated at each step. Component C3 is the key component whose

cleavage leads to the assembly of membrane attack complexes on the plasma

membrane of the microorganisms, which create holes in the plasma membrane that

lead to cell death. Various white blood cells also become activated during this process

and phagocytose the pathogen.

| Immunology |

What happens once the DNA from the HIV particle enters the cell nucleus?

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The DNA molecule, known as a provirus, assumes a relationship with the DNA of the T

lymphocyte, and the provirus enters the state of lysogeny. From this point in the

nucleus, the provirus encodes new HIV particles, which acquire their envelope by

budding through the membrane of the T lymphocyte. The human body attempts to keep

up with the mass of new viral particles, but eventually the newly emerging strains of HIV

overwhelm the body defenses and the T lymphocyte count begins to drop. Normally, it

is approximately 800 T lymphocytes per cubic millimeter of blood, but as the disease

progresses, the count drops into the low hundreds and tens. This drop may occur as

soon as weeks after infection or as long as 20 years or more after infection.

| Immunology , Microbiology |

Do antibodies have a life span in the body circulation?

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Antibodies, as noted, are protein molecules. They will either leave the body in

secretions or be broken down by enzymes that degrade proteins in the body. The

average life span of most antibody molecules is roughly a few weeks. Continued

antigen stimulation is necessary to continue the antibody response, and as the antigen

disappears, the stimulation disappears. The antibodies produced as a result of the initial

stimulation remain in the bloodstream for a long period of time, with about half the

quantity disappearing after a few weeks and half the remaining disappearing after

another few weeks, and so forth. In many cases, the antibody level is sufficient to

sustain an individual for the remainder of his or her life, especially after recovery from

disease.

| Immunology |

What is known about the structure of individual MHC genes?

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Each MHC Class I and Class II gene consists of several exons and several introns.The

most 5' exons in both Class I and Class II genes are the regulatory sequences; these

code for the factors that up-regulate the MHC gene transcription. Further downstream,

there is an exon that codes for a leader polypeptide. The role of this small polypeptide is

to target the nascent MHC molecules to the endoplasmic reticulum; when the mature

MHC molecules are ‘‘stuffed’’with peptides and ready to be expressed, the leader

polypeptide falls off. Separate exons, located 3' to the leader and in tandem array, code

for separate domains of the MHC molecule(a1, a2, and a3 in the MHC Class I and a1

and a2 or b1 and b2 in the MHC Class II molecule). Finally, the exons that code for the

MHC molecule’s transmembrane and cytoplasmic domains are also separate and

located the most 3' in an individual gene.

| Immunology |

Can substances other than proteins be antigens?

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Yes. Most antigens are proteins, but polysaccharides, certain lipids, and nucleic acids

also can trigger immune reactions. Besides, some relatively simple organic chemicals

and chemical groups can be specifically recognized by the immune system, although

they cannot trigger immune reactions. Such substances are called haptens. The

immune response specific to a hapten can be triggered if the hapten is chemically

coupled with a protein. The latter in this case will be called a carrier.

| Immunology |

Does vaccination against a disease confer active or passive immunity?

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Active immunity is conferred when the body manufactures antibodies in response to

direct contact with an antigen. When an individual is again exposed to the antigen, the

body “remembers” it and mounts a quicker and more specific antibody response to that

antigen. Active immunity can be conferred by exposure to the whole antigen (e.g., the

chicken pox virus) or by vaccination with dead or weakened pathogens or altered toxins.

Passive immunity is conferred by the transfer of antibodies from one person to

another; the recipient does not produce his or her own antibodies. For example, a

gamma globulin shot (another individual’s antibodies) can confer passive immunity

against hepatitis A. As another example, a fetus receives IgG across the placenta from

the mother. This passive immunity helps the newborn to fight disease before its own

immune system has developed.

| Immunology |

What are some of the mechanical and chemical barriers to infection?

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Mechanical barriers include skin and mucous membranes. The mucous membranes in

the respiratory passageways are lined with ciliated epithelium. The cilia continuously

move particles trapped in the mucus in a direction away from the lungs. This epithelium

is eventually destroyed in smokers, causing them to be susceptible to respiratory

diseases.

Chemical barriers:

Lysozyme—A chemical found in tears, saliva, and blood plasma that breaks down

bacterial cell walls.

Pepsin—An enzyme in the stomach that lyses (disintegrates) many microorganisms.

Hydrochloric acid—Secreted by the parietal cells in the stomach, it creates a low pH

that is lethal to many pathogens.

Complement—A series of enzymatic proteins that are activated by both specific and

nonspecific mechanisms.

Interferon—Any of a group of proteins that are produced by virus-infected cells and

some immune system cells, inhibiting viral growth.

| Biochemistry |

Showing newest posts with label Biochemistry. Show older posts

How can diseases be transmitted among various individuals?

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In order for transmission among individuals to occur, the pathogenic microorganisms

must leave the body through a portal of exit. Transmission can occur in the form of

respiratory secretions expelled from the respiratory tract, or microorganisms can exit in

the feces or urine, or they may be removed when blood is ingested by mosquitoes,

ticks, or other arthropods. Skin contact, including contact made during sexual

intercourse, is another mechanism for transport to the next individual.

| Biochemistry |

Are prokaryotes and eukaryotes similar in any respects?

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Prokaryotes and eukaryotes share common features, among them the possession of

nucleic acids and other organic substances such as proteins, carbohydrates, and lipids.

In addition, they utilize similar metabolic reactions such as glycolysis and chemiosmosis

for the utilization of food and the production of energy and waste. Also, they exhibit

many of the same physiological features such as motion and reproduction, although the

mode of reproduction may be different and different organs of motility may exist.

| Biochemistry , cell biology |

How is resolution determined in microscope?

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To determine resolution, one must know the numerical aperture (NA) of the lens

system. This denotes the size of the cone of light entering the aperture of the lens. The

NA, typically etched into the lens, is multiplied by two. The product is then divided into

the wavelength of the visible light, typically 550 nm. (If another form of light such as

ultraviolet light were used, the wavelength of that light would be used in the formula.)

The result is the resolution of the lens system expressed in nm. Conversion to

micrometers is usually the final step.

| Biochemistry |

What is bulimia?

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Bulimia is an eating disorder in which individuals binge eat frequently—often several

times a week or even several times per day. Sufferers of this illness may eat an

enormous amount of food in a short time, consuming thousands of calories. Then they

will purge their bodies by vomiting or using laxatives and/or diuretics.

| Biochemistry , Food and Nutrition |

What is diapedesis?

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Diapedesis is the ability of white blood cells to squeeze between the cells that form

blood vessel walls. Once these white blood cells are outside the blood, they move

through interstitial spaces using a form of primitive movement called amoeboid motion.

Neutrophils and monocytes are the most active of these white blood cells. These

leukocytes engulf bacterial cells, organic molecules in bacterial cells, and other large

objects such as parasites. Neutrophils and monocytes frequently become so full of

bacterial toxins and other related products that they also die.

| Biochemistry , Blood chemistry |


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What are three components necessary to maintain homeostasis?

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The three components of homeostasis are sensory receptors, integrators, and effectors.

These three components interact to maintain the state of homeostasis. Sensory

receptors are cells that can detect a stimulus that signals a change in the environment.

The brain is the integrator that processes the information and selects a response.

Muscles and glands are effectors that carry out the response

| Biochemistry |

What are the effects of Ageing on respiratory system?

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There is a decline in the efficiency of the respiratory system with ageing. There is a

gradual loss of elastic tissue & the chest wall becomes less capable of expansion.

These changes show up as a reduction in vital capacity (The maximum volume of air

that can be expired after a maximum inspiration). This may decrease by as much as

35% by the age of 70. All other aspects of function decline in performance notably, the

action of cilia & protective activity of white blood cells. This leaves the system more

prone to disease like pneumonia, bronchitis & emphysema.

| Biochemistry , physiology |


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What are the benefits of breastfeeding?

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Breastfeeding provides benefits to both the baby and the mother. A major benefit to the

baby is that breast milk supplies the correct amount of nutrients as the baby grows from

an infant to a healthy toddler. The nutrients in breast milk also protect the infant from

certain childhood illnesses. Finally, recent research has shown that breast milk contains

certain fatty acids (building blocks) that help the infant’s brain develop. In the early days

following childbirth, the mother’s body releases a hormone that makes her uterus

contract and get smaller in response to the baby’s sucking. Breastfeeding also provides

many emotional benefits between mother and child and encourages maternal-infant

bonding. Human breast milk consists of mostly of water (88 percent), sugars (6.5 to 8

percent), lipids (3 to 5 percent), proteins (1 to 2 percent), amino acids, and salts. It also

contains large quantities of lysozymes—enzymes with antibiotic properties. Human milk

is bluish-white in color and sweet. The blue color comes from the protein and the white

comes from the fat. There are approximately 750 calories per liter of breast milk.


Why is carbon so important in biological system?

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It is sometime said that life on our planet is based on carbon. Carbon is an element that

is found in all organic molecules. Carbon forms strong covalent bonds, in other words it

shares electrons, with other elements. It forms four such bonds that are it has a valency

of four. A simple example is methane, whose molecular formula is CH4. The

explanation for the importance of carbon lies in the way carbon atoms can join to each

other, forming either chain or rings. These chains & rings are the skeletons of organic

molecules & hence of life itself. They are very stable because the covalent bonds linking

the carbon atoms together are strong. Atoms or particular groups of atoms of other

elements (referred to simply as groups) can be attached at various positions to the

carbon skeleton.

| Biochemistry |

How the Urinary tract infections are differentiating?

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Urinary tract infections may occur in the urethra, where they are called urethritis; if they

occur in the bladder, they are referred to as cystitis; and if they develop in the ureters,

they are called ureteritis. Infection of the kidney is generally called pyelonephritis. In

males, inflammation of the prostate gland, called prostatitis, often accompanies urinary

tract infection. It often happens that blood infection with beta- hemolytic streptococci,

Streptococcus pyogenes, leads to inflammation in the kidney. This inflammation is

known as glomerulonephritis (also called Bright’s disease). The disease reflects an

immune complex reaction resulting from activity of the immune system and type III

hypersensitivity. Fever and high blood pressure accompany the disease.


How are the neurotransmitter molecules inactivated after they are released at a synapse?

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After a chemical neurotransmitter has been released from the synaptic terminal, its

action must be terminated in some way. Otherwise, the continued presence of the

transmitter in the extracellular space would continuously activate the post synaptic cell.

The action of a neurotransmitter can be terminated in either of 2 ways: 1) The

transmitter molecules are removed from the extracellular space by uptake into

surrounding glial cells & neurons (including the presynaptic terminal that originally

released the transmitter), as the neurotransmitter diffuses away from its site of release.

2) The neurotransmitter molecules are chemically degraded into inactive substances. At

the neurotransmitter junction, this mechanism is used to inactivate Acetylcholine

released from the synaptic terminals of the motor neurons.

| Biochemistry , Neurobiology |

How the molecular biological technique is used to study the nervous system?

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As with other fields of biology, recent advances in molecular biological technique allow

manipulations of the nervous system at the molecular level in precise & specific ways.

Also genetics has long been a valuable tool for analyzing complex biological systems &

establishing the functional role of a protein. In the nervous system, genetics has played

an important role in unraveling the molecular basis of neural function. Traditionally, the

genetic approach has relied on naturally occurring or experimentally created mutation

that affect a gene important for the biological system of interest. In the case of the

nervous system, such mutations are often detected by their effect on some aspect of

behavior. More recently, new techniques (genetic & transgenic approaches, functional

expression of genes & mutagenesis) have been developed that allow targeted

disruption of a particular gene.


What are the major hormones and aging plays any role in it?

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The major groups of hormones are amine hormones, peptide and protein hormones,

and steroid hormones. Amine hormones are relatively small molecules that are

structurally similar to amino acids. Epinephrine and norepinephrine, serotonin,

dopamine, the thyroid hormones, and melatonin are examples of amine hormones.

Peptide hormones and protein hormones are chains of amino acids. The peptide

hormones have 3 to 49 amino acids, while the protein hormones are larger with chains

of 50 to 200 or more amino acids. Examples of peptide hormones are antidiuretic

hormone and oxytocin. The larger thyroid-stimulating hormone and follicle- stimulating

hormone are examples of protein hormones. Steroid hormones are derived from

cholesterol. Cortisol and the reproductive hormones (androgens in males and estrogens

in females) are examples of steroid hormones. Most endocrine glands continue to

function and secrete hormones throughout an individual’s lifetime. The most noticeable

change in hormonal output is in the reproductive hormones. The ovaries decrease in

size and no longer respond to FSH and LH, resulting in a decrease in the output of

estrogens. Although the hormonal levels of other hormones may not change with aging

and remain within normal limits, some endocrine tissues become less sensitive to

stimulation. For example, elderly people may not produce as much insulin after a

carbohydrate-rich meal is eaten. It has been suggested that the decrease in function of

the immune system is a result of the reduced size of the thymus gland.

| Biochemistry , Endocrinolgy |

How Monoclonal Antibody differs from Polyclonal Antibody?

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If an antigen is injected into an animal, a number of antibody-producing cells will bind

that antigen albeit with varying degrees of affinity, and so the antibody which appears in

the bloodstream will have arisen from several clones of cells, that is it will be a

polyclonal antibody. Different antibody molecules in a preparation of polyclonal antibody

will bind to different parts of the macromolecular antigen and will do so with different

binding affinities. The binding region recognized by any one antibody molecule is called

an epitope. Most antibodies recognize particular surface structures in a protein rather

than specific amino acid sequences (i.e. the epitopes are defined by the conformation of

the protein antigen). A preparation of polyclonal antibodies will bind to many epitopes on

the protein antigen. Whereas, Monoclonal antibodies are single clone of antibody-

producing cells could be isolated, then all of the antibody produced from that clone

would be identical; all antibody molecules in such a monoclonal antibody preparation

would bind to the same antigen epitope. The problem is that if an individual antibody-

producing cell is isolated and grown in culture, its descendants have a limited lifespan

that severely limits their use for the routine preparation of monoclonal antibodies.

Monoclonal antibodies produced using this technology are now common tools in

research because of their very high specificity. For example, they can be used to locate

particular molecules within cells or particular amino acid sequences within proteins. If

they are first bound to an insoluble matrix, they are also extremely useful for binding to

and hence purifying the particular molecule from crude cell extracts or fractions .They

are also increasingly of use in medicine, both for diagnosis and as therapeutic tools, for

example to inactivate bacterial toxins and to treat certain forms of cancer.

| Biochemistry , Immunology |

How do bones grow?

Share|

Bones form and develop through a process called ossification. There are two types of ossification: intramembranous ossification and endochondral ossification. Intramembranous ossification is the formation of bone directly on or within the fibrous connective tissue. Examples of bone formed through intramembranous ossification are the flat bones of the skull, mandible (lower jaw), and clavicle (collarbone). Endochondral ossification, from the Greek endo, meaning “within,” and khondros,meaning “cartilage,” is the transformation of the cartilage model into bone. Cartilage cells in the epiphyseal plate grow and move into the metaphysis where they are reabsorbed and replaced by bone tissue. Examples of bone formed through endochondral ossification are the long bones, such as the femur and humerus.

| Anatomy , Biochemistry |

Why do we die without oxygen?

Share|

Most living organisms are aerobic; that is, they require oxygen to complete the total breakdown of glucose for the production of adenosine triphosphate (ATP), the energy for life. Many people think that humans need oxygen to breathe, but actually people need oxygen to recycle the spent electrons and hydrogen ions (H+) produced as byproducts of aerobic respiration.

| Biochemistry |

How does brown fat differ from white fat?

Share| White fat (or adipose tissue) stores nutrients. Brown fat, also called brown adipose tissue,

consumes its nutrient stores to generate heat to warm the body. It is called brown fat because it has a deep, rich, dark color that is derived from the numerous mitochondria in each individual cell. Brown adipose tissue is found in infants and very young children between the shoulder blades, around the neck, and in the anterior abdominal wall. Older children and adults rely on shivering to warm the body.

| Biochemistry |


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| Biochemistry , Molecular Biology , Protein


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excision repair












methyltransferase












How can drug resistance develop in microorganisms?

Share|

The use of antibiotics over the last 60 years has led to the development of drug-

resistant strains of bacteria.These bacterial strains always existed in the microbial

population, but they never needed to use their resistance mechanisms because they

were never confronted with the antibiotic. With widespread antibiotic use, the

susceptible bacteria died off rapidly, and the surviving bacteria were those with

resistance. They

quickly multiplied to form populations of drug- resistant microorganisms. While

methicillin- resistant Staphylococcus aureus (MRSA) is a well- known example of a

drug- resistant strain, many other organisms are showing alarming rates of drug

resistance due to the selective pressures exerted by the increased use of antibiotics.

| Biochemistry , cell structure , Microbiology |

Why is the Krebs cycle important in energy metabolism?

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The Krebs cycle is essential for energy metabolism because electrons are given off at

several places during the reactions of the cycle. At three different points of each cycle,

pairs of electrons are assumed by NAD molecules to produce three molecules of

reduced NAD, or NADH. In addition, another reaction yields a pair of electrons taken up

by the coenzyme FAD. This capture of electrons yields reduced FAD, or FADH2.Also

during the Krebs cycle reactions, a reaction occurs in which enough energy is liberated

to synthesize a molecule of ATP. Since two turns of the Krebs cycle occur for every

glucose molecule, two molecules of ATP are produced. These two ATP molecules are

in addition to the two ATP molecules resulting from the reactions of glycolysis.

| Biochemistry |

Nucleic acids are unique among the biopolymers in that they contain phosphate. How has this property been exploited experimentally in studies ........

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QuestionNucleic acids are unique among the biopolymers in that they contain

phosphate. How has this property been exploited experimentally in studies of protein

synthesis?

Answer

The use of 32P (radioactive) to label DNA and RNA for Southern and northern blotting

was a major technical advance. One of the earliest exploitations of the unique

phosphorus content of nucleic acids was the Waring-blender experiment (first

performed by Alfred Hershey and Martha Chase). This groundbreaking experiment

proved that DNA (and not protein) was responsible for genetic information flow from one

generation to the next. In this experiment the ability of T2 bacteriophage (a virus that

infects bacteria) to inject DNA but not protein into the host bacterium during infection

was conclusively shown with 32P labeled (which labeled the nucleic acid) and 35S

labeled (which labeled proteins only) phage. When 32P labeled phage, containing

radiolabeled DNA, were allowed to attach briefly to the host bacteria (then removed with

a Waring blender), a 32P-labeled bacterial pellet was the result obtained after

centrifugation of the sample. When 35S-labeled phage were used, the bacterial pellet

obtained after centrifugation was unlabeled. From this experiment it was finally

established that the nucleic acid and not the protein coat was transferred to the host

during viral infection. This DNA could then hijack the host’s transcription and translation

machinery to direct the synthesis of many copies of the virus, eventually leading to host

cell.

| Biochemistry |

Can hemoglobin bind other gas molecules besides oxygen?

Share|

Yes. Carbon dioxide (CO2) and carbon monoxide (CO) also bind to hemoglobin.

Hemoglobin, when saturated with oxygen, is called oxyhemoglobin. It is cherry red in

color. When oxyhemoglobin loses its oxygen, it becomes bluish purple. Hemoglobin in

combination with carbon dioxide is called carbaminohemoglobin. Oxygen and carbon

dioxide have distinct carry sites on the Hb molecule. Carbon monoxidecombined with

Hb is called carboxyhemoglobin. Carbonmonoxide binds to a heme and has 200 times

the affinity for the heme that oxygen has. It is this competitive exclusion of oxygen that

makes carbon monoxide so dangerous a gas.

| Biochemistry |

How do NADP+ and NADPH differ from NAD+ and NADH?

Share|

These pairs of molecules are identical except for the presence of a phosphate group at

the 2′ position on the ribose moiety. This is not a high-energy phosphate but rather a

molecular tag that enables enzymes to discriminate between the two forms of redox

compound. In higher animals there do not appear to be any NADH transferase enzymes

that catalyze direct transfer of hydrogen atoms from NADH to NADP+ or from NADPH

to NAD+.

NADH and NADPH are equivalent in terms of their standard redox potentials, but

because redox enzymes are usuallyselective for one or the other of them, two distinct

pools of reductants exist. NADH is used as a source of reducing

equivalents for the electron transport chain (ETC) while NADPH provides reducing

equivalents for many biosyntheticreactions. Hence, even within a single spatial

compartment such as the cytoplasm, the NADH to NAD+ ratio can be

very low, favoring oxidation of fuels, while simultaneously the NADPH to NADP+ ratio

can be very high, facilitating

biosynthesis.

| Biochemistry |

What determines the rate of an enzyme-catalyzed reaction, and why is it important?

Share|

The important factors that influence the rate of an enzymic reaction are the

concentration of the enzyme itself, the substrate concentration(s), and factors such as

pH, temperature, presence of cofactors, and metal ions. In a practical sense, there may

be occasions when we need to optimize the rate of a particular reaction.

A study of the way the rate depends on experimental variables may allow us to

discriminate between possible models that attempt to predict how the enzyme functions,

and thus to suggest ways of affecting it with antimetabolites.

| Biochemistry |

Why is HDL called “good” cholesterol and LDL “bad” cholesterol?

Share|

In contrast to LDL, HDL concentrations in the blood are inversely related to the risk of

heart disease. HDL is involved in the return of cholesterol to the liver where it is

excreted. It is not high concentrations of cholesterol per se that are necessarily

damaging to blood vessels via atherogenesis, but a high ratio of LDL:HDL. When

physicians assess cholesterol levels, they are often more interested in the ratio than the

absolute concentrations.

Atherogenic lipoproteins such as LDL enter macrophages within the blood vessel wall

and promote the growth of an atherosclerotic plaque. HDL in the plasma is

antiatherogenic and removes cholesterol from the macrophages, preventing the growth

or even regression of the atherosclerotic plaque. Aggressive targeting of lipids on both

sides of this equation, both the LDL and the HDL, is likely to be maximally effective in

reducing cardiovascular risk.The passage of HDL cholesterol back to the liver is not

without interruption. HDL particles interact with both LDLs and VLDLs, and in so doing

they exchange cholesterol for triglyceride via the actions of a protein called cholesterol

ester transfer protein and the enzyme lecithin-cholesterol acyltransferase (LCAT).

Cholesterol ester transport protein depletes HDL of cholesterol while concomitantly

increasing the amount of cholesterol in the outward-going VLDL and LDL particles. At

first glance, it may seem disadvantageous for cholesterol to remain in the atherogenic

LDL and VLDL fractions of the lipoproteins. However, the mechanism scavenges

cholesterol from the periphery, thus relieving cells of the metabolically expensive

process of de novo synthesis.

| Endocrinolgy |

How long does a hormone active once it is released?

Share|

Hormones that circulate freely in the blood remain functional for less than one hour.

Some hormones are functional for as little as two minutes. A hormone becomes

inactivated when it diffuses out of the bloodstream and binds to receptors in target

tissues or is absorbed and broken down by cells of the liver or kidneys. Enzymes in the

plasma or interstitial fluids that break down hormones also cause them to become

inactivated. Other hormones (e.g., renin) are activated by enzymes that cleave the

active portion from a larger circulating precursor molecule.

| Endocrinolgy |

What is mixed gland?

Share|

The pancreas is a mixed gland because it has both endocrine and exocrine functions.

As an endocrine gland, it secretes hormones into the bloodstream. Only one percent of

the weight of the pancreas serves as an endocrine gland. The remaining 99 percent of

the gland has exocrine functions. The acinar cells (also called acini, from the Latin

meaning “grapes” because their structure resembles clusters of grapes) are responsible

for secreting digestive enzymes.The pancreatic islets (islet of Langerhans) are cluster

cells that secrete hormones. There are between 200,000 and 2,000,000 pancreatic

islets scattered throughout the adult pancreas.

| Endocrinolgy |

How long does a hormone remain active after it is released?

Share|

Hormones that circulate freely in the blood remain functional for less than one hour.

Some hormones are functional for as little as two minutes. A hormone becomes

inactivated when it diffuses out of the bloodstream and binds to receptors in target

tissues or is absorbed and broken down by cells of the liver or kidneys. Enzymes in the

plasma or interstitial fluids that break down hormones also cause them to become

inactivated. Other hormones (e.g., renin) are activated by enzymes that cleave the

active portion from a larger circulating precursor molecule

| Endocrinolgy |

What is the difference between a sexually transmitted disease and a sexually transmitted infection?

Share|

The term “sexually transmitted disease” (STD) has been used frequently to describe

infections of the reproductive tract. The term “disease” typically implies that symptoms

are present such that the individual would be aware that an infection was present.

However, the term “sexually transmitted infection” (STI) is currently favored. Using the

STI term implies that infection can be present without the symptoms of disease.

Because many infections of the reproductive tract can be asymptomatic, the term STI is

often more appropriate than STD.

| Endocrinolgy |

Which is the predominant in Thyroid hormone?

Share|

Thyroxine, or T4, also called tetraiodothyronine, contains four atoms of iodine.

Triiodothyronine, or T3, contains only three atoms of iodine. The more common

hormone is T4, which accounts for nearly 90 percent of the secretions from the thyroid.

The amount of T3 in the body is concentrated and very effective. Both hormones have

similar functions. Enzymes in the liver can convert T4 to T3.

| Endocrinolgy |

What are the major hormones and aging plays any role in it?

Share|

The major groups of hormones are amine hormones, peptide and protein hormones,

and steroid hormones. Amine hormones are relatively small molecules that are

structurally similar to amino acids. Epinephrine and norepinephrine, serotonin,

dopamine, the thyroid hormones, and melatonin are examples of amine hormones.

Peptide hormones and protein hormones are chains of amino acids. The peptide

hormones have 3 to 49 amino acids, while the protein hormones are larger with chains

of 50 to 200 or more amino acids. Examples of peptide hormones are antidiuretic

hormone and oxytocin. The larger thyroid-stimulating hormone and follicle- stimulating

hormone are examples of protein hormones. Steroid hormones are derived from

cholesterol. Cortisol and the reproductive hormones (androgens in males and estrogens

in females) are examples of steroid hormones. Most endocrine glands continue to

function and secrete hormones throughout an individual’s lifetime. The most noticeable

change in hormonal output is in the reproductive hormones. The ovaries decrease in

size and no longer respond to FSH and LH, resulting in a decrease in the output of

estrogens. Although the hormonal levels of other hormones may not change with aging

and remain within normal limits, some endocrine tissues become less sensitive to

stimulation. For example, elderly people may not produce as much insulin after a

carbohydrate-rich meal is eaten. It has been suggested that the decrease in function of

the immune system is a result of the reduced size of the thymus gland.

| Biochemistry , Endocrinolgy |

| Food and Nutrition

Can someone die from excessive water intake?

Share|

Excessive water intake is known as water intoxication and is the direct result of drinking

too much water at too quickly a rate. The excess water greatly dilutes the nutrients and

ions in the body. The result is that the body cannot carry out its functions. In particular,

when the sodium ion concentrationdecreases, hyponatremia occurs, which may lead to

coma and death

| Food and Nutrition |

What is bulimia?

Share|

Bulimia is an eating disorder in which individuals binge eat frequently—often several

times a week or even several times per day. Sufferers of this illness may eat an

enormous amount of food in a short time, consuming thousands of calories. Then they

will purge their bodies by vomiting or using laxatives and/or diuretics.


What are the benefits of breastfeeding?

Share|

Breastfeeding provides benefits to both the baby and the mother. A major benefit to the

baby is that breast milk supplies the correct amount of nutrients as the baby grows from

an infant to a healthy toddler. The nutrients in breast milk also protect the infant from

certain childhood illnesses. Finally, recent research has shown that breast milk contains

certain fatty acids (building blocks) that help the infant’s brain develop. In the early days

following childbirth, the mother’s body releases a hormone that makes her uterus

contract and get smaller in response to the baby’s sucking. Breastfeeding also provides

many emotional benefits between mother and child and encourages maternal-infant

bonding. Human breast milk consists of mostly of water (88 percent), sugars (6.5 to 8

percent), lipids (3 to 5 percent), proteins (1 to 2 percent), amino acids, and salts. It also

contains large quantities of lysozymes—enzymes with antibiotic properties. Human milk

is bluish-white in color and sweet. The blue color comes from the protein and the white

comes from the fat. There are approximately 750 calories per liter of breast milk.


Can microorganisms be used to produce vitamins and amino acids?

Share|

Numerous vitamins are currently produced by industrial fermentations. Vitamin B12, for

example, is used to prevent certain types of anemia in the body, and riboflavin is used

to encourage metabolic processes in the body. Both are produced by bacteria cultivated

in industrial plants. Yeasts are rich in B vitamins and are used as a food supplement.

Among the amino acids produced by microorganisms in industrial processes are

glutamic acid and lysine. Both are used as dietary growth supplements.

| Food and Nutritio

| physiology | How does blood circulate in the fetus?

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| physiology |

Why is a man’s voice usually lower than a woman’s voice?

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Does your heart stop beating when you sneeze?

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The heart does not stop beating when you sneeze. Sneezing, however, does affect the

cardiovascular system. It causes a change in pressure inside the chest. This change in

pressure affects the blood flow to the heart, which in turn affects the heart’s rhythm.

Therefore, a sneeze does produce a harmless delay between one heartbeat and the

next, often misinterpreted as a “skipped beat.”

| physiology |


Share|














Is all the cartilage in the body the same?

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There are three types of cartilage in the human body: 1) hyaline cartilage; 2) elastic

cartilage; and 3)fibrocartilage. Hyaline cartilage (from the Greek hyalos, meaning

“glass”) is the most common type of cartilage in the body. It has a translucent, pearly,

blue-white appearance resembling glass. Hyaline cartilage provides stiff but flexible

support and reduces friction between bony surfaces. It is found between the tips of the

ribs and the bones of the sternum, at the end of the long bones, at the tip of the nose,

and throughout the respiratory passages. Elastic cartilage is similar to hyaline cartilage

except it is very flexible and resilient. It is ideal for areas that need repeated bending

and stretching. Elastic cartilage forms the external flap of the outer ear and is found in

the auditory canal and epiglottis. Fibrocartilage is often found where hyaline cartilage

meets a ligament or tendon. It is found in the pads of the knees, between the pubic

bones of the pelvis, and between the spinal vertebrae. It prevents bone-to-bone contact.

Cartilage does not contain blood vessels. Oxygen, nutrients, and cellular wastes diffuse

through the selectively permeable matrix. Cartilage transplants are successful because

foreign proteins in the transplanted cells do not have a way to enter the host body’s

circulation and cause an immune response. However, since there are no blood vessels

in cartilage, the healing process is slower than for other tissues


Which types of tissue have the greatest capacity to regenerate?

Share|

Epithelial and connective tissues have the greatest capacity to regenerate. In small

wounds and injuries, the epithelial and connective tissues often heal with normal tissue.

The ability of muscle tissue to regenerate is very limited. Fibrous connective tissue often

replaces damaged muscle tissue. As a consequence, the organ involved loses all or

part of its ability to function. Nerve tissue has even less capacity to regenerate.

Although neurons outside the brain and spinal cord sometimes regenerate at a very

slow pace, most brain and spinal cord injuries result in permanent damage.


What are the effects of Ageing on respiratory system?

Share|

There is a decline in the efficiency of the respiratory system with ageing. There is a

gradual loss of elastic tissue & the chest wall becomes less capable of expansion.

These changes show up as a reduction in vital capacity (The maximum volume of air

that can be expired after a maximum inspiration). This may decrease by as much as

35% by the age of 70. All other aspects of function decline in performance notably, the

action of cilia & protective activity of white blood cells. This leaves the system more

prone to disease like pneumonia, bronchitis & emphysema.


How the Urinary tract infections are differentiating?

Share|

Urinary tract infections may occur in the urethra, where they are called urethritis; if they

occur in the bladder, they are referred to as cystitis; and if they develop in the ureters,

they are called ureteritis. Infection of the kidney is generally called pyelonephritis. In

males, inflammation of the prostate gland, called prostatitis, often accompanies urinary

tract infection. It often happens that blood infection with beta- hemolytic streptococci,

Streptococcus pyogenes, leads to inflammation in the kidney. This inflammation is

known as glomerulonephritis (also called Bright’s disease). The disease reflects an

immune complex reaction resulting from activity of the immune system and type III

hypersensitivity. Fever and high blood pressure accompany the disease.


What is rigor mortis?

Share|

Dead bodies are at first limp. Several hours after death, the skeletal muscles undergo a

partial contraction that fixes the joints. This condition, known as rigor mortis, may

continue for 72 hours or more. When neurons signal living muscle fibers to contract,

they do so with a neurotransmitter that is received at the surface of the muscle fiber.

The signal makes the fiber open calcium ion channels, and it is the calcium that causes

the contraction. The muscle then removes the calcium in two ways: it stores some in its

mitochondria, and it pumps out the rest. When a body dies, stored calcium leaks and

calcium pumps no longer function. The excess calcium causes the actin and myosin

filaments of the muscle fibers to remain linked, stiffening the whole body until the

muscles begin to decompose.


How does the endocrine system differ from the nervous system?

Share|

Both the endocrine and nervous are regulatory systems that permit communication between cells, tissues, and organs. A major difference between the endocrine system and nervous system is the rate of response to a stimulus. In general, the nervous system responds to a stimulus very rapidly, often within a few milliseconds, while it may take the endocrine system seconds and sometimes hours or even days to offer a response. Furthermore, the chemical signals released by the nervous system typically act over very short distances (a synapse), while hormones in the endocrine system are generally carried by the blood to target organs. Finally, the effects of the nervous system generally last only a brief amount of time, while those of the endocrine system are longer lasting. Examples of endocrine control are growth and reproductive ability.

| physiology |

Which is the only bone that does not touch another bone?

Share|

The hyoid bone is the only bone that does not touch another bone. Located above the

larynx, it supports the tongue and provides attachment sites for the muscles of the neck

and pharynx used in speaking and swallowing. The hyoid is carefully examined when

there is a suspicion of strangulation, since it is often fractured from such trauma.

| physiology |

Are smooth muscle contractions the same as skeletal muscle contractions?

Share|

There are similarities, as well as differences, in comparing smooth and skeletal muscle

contractions. Both types of muscles include reactions involving actin and myosin, both

are triggered by membrane impulses and an increase in intracellular calcium ions, and

both use energy from ATP (adenosine triphosphate). One difference between smooth

and skeletal muscle contractions is that smooth muscle is slower to contract and to

relax than skeletal muscle. Smooth muscle can maintain a forceful contraction longer

with a set amount of ATP. In addition, smooth muscle fibers can change length without

changing tautness (as when the stomach is full), while this does not occur in skeletal

muscles.

| physiology |

Which neurotransmitter is depleted in Parkinson’s disease?

Share|

Parkinson’s disease results from a deficiency of the neurotransmitter dopamine in certain brain neurons that regulate motor activity. Parkinson’s disease is characterized by stiff posture, tremors, slowness of movement, postural instability, and reduced spontaneity of facial expressions. There is no cure for Parkinson’s disease, but certain medications provide relief from the symptoms by increasing the amount of dopamine in the brain. Patients are usually given levodopa combined with carbidopa. Carbidopa delays the conversion of levodopa into dopamine until it reaches the brain. Nerve cells can use levodopa to make dopamine and replenish the brain’s dwindling supply.

| physiology |

Why is the blood-brain barrier important?

Share|

The blood-brain barrier is formed by the contacts of special glial cells, called astrocytes,

with blood vessels. It is essential for maintaining homeostasis in the brain. In general,

only lipid-soluble molecules, such as carbon dioxide, oxygen, steroids, and alcohols,

can pass through the blood-brain barrier easily. Water-soluble molecules, such as

sodium, potassium, and chloride ions can pass through the blood-brain barrier only with

the assistance of specific carrier molecules. Some substances cannot pass through the

barrier at all.

| physiology |

Do creatine supplements improve muscular performance?

Share|

Creatine phosphate (CP) is a molecule stored in muscle that yields energy when the creatine splits from the attached phosphate. This energy is used to resynthesize the small amount of ATP (adenosine triphosphate) that is available to the muscle in the initial seconds of high intensity work (think 100-yard dash or a power lift). Because greater amounts of CP in the muscle can potentially allow for those high intensity efforts to be sustained a bit longer or to be performed more effectively, creatine supplementation has become popular within the last 15 years. Some research indicates that such supplementation can improve performance in the short term and in high intensity activities, but for more sustained activities it has little or no effect because of the ATP’s great dependence on aerobic metabolism. The long-term effect of such supplementation on the human body is unknown.

| Pharmacology , physiology |


Share|

Several general differences exist between the male and female skeletons. The male skeleton is generally larger and heavier than the female skeleton. The bones of the skull are generally more graceful and less angular in the female skeleton. A female also has a wider, shorter breastbone and slimmer wrists. There are significant differences between the pelvis of a female and a male, which are related to pregnancy and childbirth. The female pelvis is wider and shallower than the male pelvis. Females have an enlarged pelvic outlet and a wider, more circular pelvic inlet. The angle between the pubic bones is much sharper in males, resulting in a more circular, narrower, almost heart-shaped pelvis.

| physiology |

Is brain size an indication of intelligence? How the size changes from birth to adulthood?

Share|

There is no correlation between brain size and intelligence. Individuals with the smallest brains (as small as 46 cubic inches [750 cubic centimeters]) and the largest brains (as large as 128 cubic inches [2,100 cubic centimeters]) have the same functional intelligence.

Brain cells grow in size and degree of myelination as a child grows from birth to adulthood. Although the number of neurons does not increase after infancy, the number of glial cells does increase. An adult brain is approximately three times as heavy as it was at birth. Between ages 20 and 60, the brain loses approximately 0.033 to 0.10 ounces (1 to 3 grams) a year as neurons die and are not replaced. After age 60 the annual rate of shrinkage increases to 0.10 to 0.143 ounces (3 to 4 grams) per year.

| physiology |

Are cells in the nervous system replaced during an individual’s lifetime?

Share|

Neurons have a very limited capacity for regeneration. In general, they neither replicate themselves nor repair themselves. Axons and dendrites in the peripheral nervous system may undergo repair if the cell body is intact and if the Schwann cells are functional. In the central nervous system, however, a damaged or cut axon is usually not repaired even when the cell body is intact and undamaged. Scientists have discovered recently that there are a few small concentrations of neuronal stem cells that remain in adults that can produce a limited number of new neurons.

| physiology |

Newer PostsOlder PostsHome

How sex occurs in bacteria?

Share|

The occurrence of sex in bacteria was first described by Joshua Lederberg and Edward

Tatum in 1946 (Nature, volume 158, page 558), who were studying mixed cultures of E.

coli strains with various nutritional mutations. The mutant strains differed from the wild

type strains in lacking the ability to synthesize growth factors such as amino acids and

vitamins, similar to the strains in the present problem.

In one experiment, two triple mutants of E. coli, one requiring threonine, leucine, and

thiamine, and the second requiring biotin, phenylalanine, and cystine were grown in

mixed cultures. At very low frequency, recombinant strains with no growth-factor

requirement were obtained. They ruled out spontaneous mutations and transformation

by the culture medium as the source of recombinant strains. In the words of Lederberg

and Tatum, "These experiments imply the occurrence of a sexual process in the

bacterium Escherichia coli."

| bacteriology , Molecular Biology |


| Blood Chemistry |

What is diapedesis?

Share|

Diapedesis is the ability of white blood cells to squeeze between the cells that form

blood vessel walls. Once these white blood cells are outside the blood, they move

through interstitial spaces using a form of primitive movement called amoeboid motion.

Neutrophils and monocytes are the most active of these white blood cells. These

leukocytes engulf bacterial cells, organic molecules in bacterial cells, and other large

objects such as parasites. Neutrophils and monocytes frequently become so full of

bacterial toxins and other related products that they also die.

| Biochemistry , Blood chemistry |

Why are red blood cells disc shaped ?

Share|

Red blood cells are perhaps the most specialized cells in the human body. They are a

biconcave (donut) shape with a thin central disc. This shape is important because the

disc increases the surface-area-to-volume ratio for faster exchange of gases and it

allows red blood cells to stack, one on another, as they flow through very narrow

vessels. Also, since some capillaries are as narrow as 0.00015748 inches (0.004

millimeters), red blood cells can literally squeeze through narrow vessels by changing

shape.

Animal Behaviour

What hormone can be used to overcome jet lag?

Share|

Jet lag occurs when an individual’s biological clock is out of sync with local time. As a

general rule it takes about a day for each hour of time zone change to recover from jet

lag. Melatonin, available as a dietary supplement, is sometimes used to induce sleep

when traveling. It is more useful when traveling east and may be taken before, during,

or after traveling. It is best taken approximately five to seven hours before the usual

bedtime in the old time zone. Travelers should consult their physicians before using

melatonin. It is not recommended for pregnant or breast-feeding women and children.

| Anatomy , Animal Behaviour |

Are humans the only animals who can think?

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Before one can answer this question, one must define what is meant by thought.

Thought can be defined in several ways: is it philosophical rumination or the processing

of perceptions of the natural world? Because we are still trying to translate animal

communication into human language, it is difficult to provide definitive proof of

philosophical thought processes. Current studies by animal behaviorists indicate that

animals that have a varied social life (such as chimpanzees) perceive the world in ways

similar to humans. However, since we do not share a common verbal language with

animals, it is impossible to know what they are thinking.

| Animal Behaviour , Evolution

Neurobiology |

How many cranial nerves are in the human body?

Share|

The cranial and spinal nerves constitute the somatic peripheral nervous system. These

nerves connect the brain and spinal cord to peripheral structures such as the skin

surface and the skeletal muscles. The peripheral nerves measure approximately 93,000

miles (150,000 kilometers) in length.There are twelve pairs of cranial nerves in the

human body. The cranial nerves are designated by Roman numerals and names. The

Roman numerals indicate the order in which they emerge from the brain. The name

indicates an anatomical feature of function. The trigeminal nerve is the largest, although

not the longest, cranial nerve.

| Neurobiology |

How are the neurotransmitter molecules inactivated after they are released at a synapse?

Share|

After a chemical neurotransmitter has been released from the synaptic terminal, its

action must be terminated in some way. Otherwise, the continued presence of the

transmitter in the extracellular space would continuously activate the post synaptic cell.

The action of a neurotransmitter can be terminated in either of 2 ways: 1) The

transmitter molecules are removed from the extracellular space by uptake into

surrounding glial cells & neurons (including the presynaptic terminal that originally

released the transmitter), as the neurotransmitter diffuses away from its site of release.

2) The neurotransmitter molecules are chemically degraded into inactive substances. At

the neurotransmitter junction, this mechanism is used to inactivate Acetylcholine

released from the synaptic terminals of the motor neurons.


How the molecular biological technique is used to study the nervous system?

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As with other fields of biology, recent advances in molecular biological technique allow

manipulations of the nervous system at the molecular level in precise & specific ways.

Also genetics has long been a valuable tool for analyzing complex biological systems &

establishing the functional role of a protein. In the nervous system, genetics has played

an important role in unraveling the molecular basis of neural function. Traditionally, the

genetic approach has relied on naturally occurring or experimentally created mutation

that affect a gene important for the biological system of interest. In the case of the

nervous system, such mutations are often detected by their effect on some aspect of

behavior. More recently, new techniques (genetic & transgenic approaches, functional

expression of genes & mutagenesis) have been developed that allow targeted

disruption of a particular gene.

|

| dermatology |

How is hair color determined and why it turns grey?

Share|

Genes determine hair color by directing the type and amount of pigment that epidermal

melanocytes produce. If these cells produce an abundance of melanin, the hair is dark.

If an intermediate quantity of pigment is produced, the hair is blond. If no pigment is

produced, the hair appears white. A mixture of pigmented and unpigmented hair is

usually gray. Another pigment, trichosiderin, is found only in red hair. The pigment in

hair, as well as in the skin, is called melanin. There are two types of melanin:

eumelanin, which is dark brown or black, and pheomelanin, which is reddish yellow.

Both are made by a type of cell called a melanocyte that resides in the hair bulb and

along the bottom of the outer layer of skin, or epidermis. The melanocytes pass this

pigment to adjoining epidermal cells called keratinocytes, which produce the protein

keratin—hair’s chief component. When the keratinocytes eventually die, they retain the

melanin. Thus, the pigment that is visible in the hair and in the skin lies in these dead

keratinocyte bodies. Gray hair is simply hair with less melanin, and white hair has no

melanin at all. It remains unclear as to how hair loses its pigment. In the early stages of

graying, the melanocytes are still present but inactive. Later, they seem to decrease in

number. Genes control this lack of deposition of melanin. In some families, many

members’ hair turns white in their 20s. Generally speaking, among Caucasians 50

percent are gray by age 50. There is, however, wide variation. Premature gray hair is

hereditary, but it has also been associated with smoking and vitamin deficiencies. Early

onset of gray hair (from birth to puberty) is often associated with various medical

syndromes, including dyslexia.

| cosmetology , dermatology |

What are age spots?

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Age spots—also known as sunspots, liver spots, or lentigines—are caused by long term exposure to the sun. Age spots are flat, irregular, brown discolorations of the skin that usually occur on the hands,neck, and face of people older than forty. They are not harmful and are not cancerous

| dermatology |

Which layers of skin are damaged by burns?

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Burns may be caused by heat generated by radioactive, chemical, or electrical agents.

Two factors affect burn severity: the depth of the burn and the extent of the burned

area. There are three categories of burns: First-degree burns—Burns that are red and

painful, but not swollen and blistering, such as from a sunburn, and damage only the

epidermis. Second-degree burns—Burns that are red, painful, and blistering, these

burns involve injury to the epidermis and the upper region of the dermis. Third-degree

burns—Burns that are severely painful, giving the skin a white or charred appearance;

they destroy all layers of the skin, including blood vessels and nerve endings. Skin

damaged by third-degree burns does not regenerate. Damage to the skin affects the

body’s ability to retain fluids.

| dermatology , surgery |

| Gynacology |


Share|

Several general differences exist between the male and female skeletons. The male

skeleton is generally larger and heavier than the female skeleton. The bones of the skull

are generally more graceful and less angular in the female skeleton. A female also has

a wider, shorter breastbone and slimmer wrists. There are significant differences

between the pelvis of a female and a male, which are related to pregnancy and

childbirth. The female pelvis is wider and shallower than the male pelvis. Females have

an enlarged pelvic outlet and a wider, more circular pelvic inlet. The angle between the

pubic bones is much sharper in males, resulting in a more circular, narrower, almost

heart-shaped pelvis

| Anatomy , Gynacology |


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What is the general course of development for cases of syphilis?

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The etiologic agent of syphilis is the spirochete Treponema pallidum. The organism is

motile and can be observed moving about under the dark- field microscope. It is

extremely difficult to cultivate in the laboratory, and direct observation is usually required

for diagnosis. The organism is transmitted among humans by sexual contact, such as

during sexual intercourse.

The development of syphilis is generally an involved series of events. The primary stage

consists of a painless, hard sore called a chancre at the site where spirochetes have

entered the body(usually on the external or internal genital organs). After several

weeks, the chancre disappears and a latent period ensues. The secondary stage

appears many weeks or months later. The secondary stage is accompanied by a skin

rash with pustular lesions and skin eruptions. The hair on the head and eyebrows is

often lost. Liver inflammation is common, and an influenza like syndrome may appear.

The person is highly contagious at this point. After some time, the lesions heal and

another latent stage develops. A tertiary stage may appear years later. This stage is

characterized by the formation of gummas, which are gummy, granular lesions that

form in the brain and major blood vessels. The patient often becomes paralyzed and

usually suffers permanent damage to the blood vessels. In addition, the symptoms of

dementia may occur. Death usually accompanies destruction of the heart and blood

vessel tissues.

One of the dangers of syphilis is the possible development of congenital syphilis. In this

instance, the spirochetes cross the placenta and enter the fetal blood from the mother’s

blood. Newborns show signs such as notched incisors (Hutchinson’s teeth), a

perforated palate, an aged- looking face, and damage to the nose. Congenital syphilis

may also result in stillbirth.

Virology


Share|

When physicians in Los Angeles and other cities noted an unusually large number of

opportunistic microbial infections. Destruction of T lymphocytes of the immune system

cells were associated with these infections, and it soon became obvious that an

epidemic of disease was in progress. By 1984 the responsible virus had been identified,

and in 1986 it was given the name human immunodeficiency virus (HIV). HIV is a very

fragile virus, and for this reason it does not survive long periods of exposure outside the

body.

In infected individuals, HIV infects T lymphocytes by combining its spike glycoproteins

with the CD4 receptor sites of T lymphocytes. The nucleocapsid enters the cytoplasm of

the T lymphocyte, and the viral enzyme reverse transcriptase synthesizes a DNA

molecule using the RNA of HIV as a template (for this reason, the virus is called a

retrovirus). The DNA molecule migrates to the cell nucleus and becomes part of a

chromosome in the T lymphocyte nucleus.









soon as weeks after infection or as long as 20 years or more after infection. Thus far,

vaccines are not available against HIV. Two glycoproteins called gp120 and gp160 from

the envelope are being investigated as possible vaccines. Vaccine development is

hampered however, since it is difficult to find volunteers who would become antibody-

positive and could suffer discrimination as a result of antibody presence. Nevertheless,

candidate vaccines have been prepared with gp120 and gp160. Many candidate

vaccines are now in the testing stage

General How an enzyme synthesis & breakdown is regulated?

Share|

The amount of a particular enzyme present in a cell or tissue changes according to the

rates of its synthesis and degradation. Factors affecting the rate of synthesis include the

level of induction or repression of the gene encoding the enzyme and also the rate of

degradation of the mRNA produced from that gene. Many key enzymes at control points

in metabolic pathways have particularly short-lived mRNAs and the rate of enzyme

synthesis is thus readily controlled by factors that affect the rate of gene transcription.

The rate of degradation of an enzyme is reflected in its half-life – the time taken for 50%

of the protein to be degraded. Most enzymes that are important in metabolic regulation

have short half-lives, and are termed labile enzymes.

Do cardiac muscle cells continue to divide throughout a person’s life?

Share|

The vast majority of heart muscle cells are thought to stop dividing by the time a person reaches the age of nine. These cells then pump blood for the rest of a healthy person’s life. In people stricken by a heart attack, the cells die and are replaced by scar tissue.

| cardiology |


Share|

Creatine phosphate (CP) is a molecule stored in muscle that yields energy when the creatine splits from the attached phosphate. This energy is used to resynthesize the small amount of ATP (adenosine triphosphate) that is available to the muscle in the initial seconds of high intensity work (think 100-yard dash or a power lift). Because greater amounts of CP in the muscle can potentially allow for those high intensity efforts to be sustained a bit longer or to be performed more effectively, creatine supplementation has become popular within the last 15 years. Some research indicates

that such supplementation can improve performance in the short term and in high intensity activities, but for more sustained activities it has little or no effect because of the ATP’s great dependence on aerobic metabolism. The long-term effect of such supplementation on the human body is unknown.


What are Killed (inactivated) vaccines?

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When safe live vaccines are not available, either because attenuated strains have not

been developed or else because reversion to wild type occurs too readily, it may be

possible to use an inactivated preparation of the virulent organism to immunize the host.

The organism is propagated in bulk, in vitro, and inactivated with either

betapropiolactone or formaldehyde. These vaccines are not infectious and are therefore

relatively safe. However, they are usually of lower immunogenicity and multiple doses

may be needed to induce immunity. In addition, they are usually expensive to prepare.

In subcellular fractions ,when protective immunity is known to be directed against only

one or two proteins of an organism, it may be possible to use a purified preparation of

these proteins as a vaccine. The organism is grown in bulk and inactivated, and then

the protein of interest is purified and concentrated from the culture suspension. These

vaccines are safe and fewer local reactions occur at the injection site. However, the

same disadvantages of poor immunogenicity and the need for multiple boosters apply.

| Microbiology , Pharmacology |

What is triclosan?

Share|

Triclosan has properties of a phenol and is extremely popular in antibacterial products

such as hand sanitizers, antibacterial soaps, lotions, toothpastes, and even as an

antimicrobial additive in plastics. Resistance to triclosan occurs in some bacterial

species, and there is concern that resistance to triclosan may provide cross- resistance

to antibiotics. This is of particular concern with antibiotic resistant strains of

Staphylococcus aureus.

| Pharmacology |

How are fingerprints used for computer security and why?

Share| An individual’s fingerprints remain the same throughout his or her entire life. Minor cuts or

abrasions, and some skin diseases such as eczema or psoriasis, may cause temporary

disturbances to the fingerprints, but upon healing the fingerprints will return to their original pattern. More serious injuries to the skin that damage the dermis might leave scars that change or disrupt the ridge pattern of the fingerprints, but examining the skin outside the area of damage will reveal the same fingerprint pattern.

Recent technological advances using optical scanners and solid-state readers use software to analyze the geometric pattern of fingerprints and compare it with those of registered, legitimate users of a network system.Less expensive models of these devices have false acceptance rates of less than 25 per million and false rejection rates of less than three percent.Possible applications include using fingerprints instead of passwords for computers, linking to individual bank accounts and automated teller machines, and for credit cards and Internet transactions.

| criminology , Facts |

Why is a woman’s voice usually higher than a man’s voice?

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| Anatomy , Facts |

Why is it dangerous to talk while eating?

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If a person talks while eating, food may be inhaled into the lungs. Normally, after food is

swallowed, it passes into the pharynx and then into the esophagus. Food is prevented

from entering the larynx (the passageway to the lungs) by the epiglottis, a spade-

shaped cartilage flap that covers the pharynx. If food does enter the larynx, a cough

reflex is usually initiated, although food may lodge in the larynx, causing a blockage of

the airway.

| Anatomy , Facts |

How is IQ calculated?

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IQ, or the intelligence quotient, was originally computed as the ratio of a person’s

mental age to his chronological age, multiplied by 100. Following this method, a child of

10 years old who performed on the test at the level of an average 12 year old (mental

age of 12), was assigned an IQ of 12/10 x 100 = 120. More recently, the concept of

“mental age” has fallen into disrepute and IQ is computed on the basis of the statistical

percentage of people who are expected to have a certain IQ. An IQ of 100 is considered

average. An IQ of 70 or below indicates mental retardation, and an IQ of 130 or above

indicates gifted abilities.

| Facts |

What information can a forensic scientist determine from a human hair?

Share|

A single strand of human hair can identify the age and sex of the owner, drugs and

narcotics the individual has used (up to 90 days previously), and, through DNA

evaluation and sample comparisons, from whose head the hair came.

| Genetics , Technology |

What is a gene chip?

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Agene chip is part of the process of microarray profiling; it is also known as a biochip or

a DNA chip. It is about the size of a postage stamp and is based on a glass

wafer,holding as many as 400,000 tiny cells. Each tiny cell can hold DNA from a

different human gene and can perform thousands of biological reactions in a few

seconds.These chips can be used by pharmaceutical companies to discover what

genes are involved in various disease processes. They can also be used to type single

nucleotide polymorphisms (SNPs), which are base pair differences that are found

approximately every 500 to 1,000 base pairs in DNA. There are more than 3 million

SNPs in the human genome. They are very important in DNA typing because they

represent about 98 percent of all DNA polymorphisms.

| Technology |

Why is there a “popping” sound when you crack your knuckles, and is it dangerous to crack them?

Share|

A number of reasons have been given for the characteristic “popping” sound associated with someone cracking their knuckles. One reason is that

when a joint is contracted, small ligaments or muscles may pull tight and snap across the bony protuberances of the joint. Another possibility is that when the joint is pulled apart, air can pop out from between the bones, creating a vacuum that produces a popping sound. A third reason, discovered by British scientists in 1971, is that when the pressure of the synovial fluid is reduced by the slow articulation of a joint tiny gas bubbles in the fluid may burst, producing the popping sound. Research has not shown any connection between knuckle cracking and arthritis. One study found that knuckle cracking may be the cause of soft tissue damage to the joint capsule and a decrease in grip strength. The rapid, repeated stretching of the ligaments surrounding the joint is most likely the cause of damage to the soft tissue. Some researchers believe that since the bones of the hand are not fully ossified until approximately age 18, children and teenager who crack their knuckles may deform and enlarge the knuckle bones. However, most researchers believe knuckle cracking does not cause serious joint damage.

| Anatomy , Psycology |

What are the stages of sleep?

Share| Data collected from EEGs (electroencephalograms) of brain activity during sleep have shown at

least four separate stages of sleep. During stage 1, heart and breathing rates decrease slightly, the eyes roll slowly from side to side, and an individual experiences a floating sensation. Stage 1 sleep is not usually classified as “true” sleep. This stage generally lasts only five minutes. Individuals awakened during stage 1 sleep will often insist that they were not sleeping, but merely “resting their

eyes.” Stage 2 sleep is characterized by the appearance of short bursts of waves known as “sleep spindles” along with “K complexes,” which are high-voltage bursts that occur before and after a sleep spindle. Eyes are generally still and

heart and breathing rates decrease only slightly. Sleep is not deep. Stage 3 sleep is intermediate sleep and is characterized by steady, slow breathing, a slow pulse rate, and a decline in temperature and blood pressure. Only a loud noise awakens sleepers in stage 3 sleep. Stage 4 sleep, known as oblivious sleep, is the deepest stage. It usually does not begin until about an hour after falling asleep. Brain waves become even slower, and heart and breathing rates drop to 20 or 30 percent below those in the waking state. The sleeping individual in stage 4 sleep is not awakened by external stimuli, such as noise, although an EEG will indicate that the brain acknowledges such stimuli. Stage 4 sleep continues for close to an hour, after which the sleeper will gradually drift back into stage 3 sleep, followed by stages 2 and then 1, before the cycle begins again.

| Psycology |

What is seasonal affective disorder (SAD)?

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Seasonal affective disorder is a type of depression that affects some individuals during

the winter months when there is less sunlight. One hypothesis is that since there are

fewer hours of daylight during the winter months, the production of melatonin is

affected, resulting in physical ailments such as drowsiness and lethargy. Additional

symptoms of SAD include a craving for carbohydrates, increased appetite, weight gain,

and mood swings. Many researchers believe light therapy is an effective treatment for

SAD. Light therapy, also called phototherapy, involves sitting near a specially designed

light box that produces a strong light. Most light boxes emit a light of 2,500 to 10,000

lux, which is between the average living room lighting of 100 lux and a bright sunny day

of about 100,000 lux.

| Psycology |

Why is it difficult to remember dreams?

Share|

Almost all dreams occur during REM (rapid eye movement )sleep. Scientists do not

understand why dreaming is important, one theory is that the brain is either cataloging

the information it acquired during the day and discarding the data it does not want, or is

creating scenarios to work through situations causing emotional distress. Regardless of

its function, most people who are deprived of sleep or dreams become disoriented,

unable to concentrate, and may even have hallucinations.

It appears that the content of dreams is stored in short-term memory and cannot be

transferred into long-term memory unless they are somehow articulated. Sleep studies

show that when individuals who believe they never dream are awakened at various

intervals during the night when they are in the middle of a dream.

| Psycology |

Why is chemistry important for understanding the human body?

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The universe and everything in it is composed of matter. Matter is anything that

occupies space and has mass. The 92 naturally occurring chemical elements are the

fundamental forms of matter. Twenty-six different elements are found in the human

body. The continually ongoing chemical reactions in the body underlie all physiological

processes of the body, including movement, digestion, the pumping of the heart,

respiration, and sensory and neural processes.

| chemistry |

How do chloroplasts work?

Share|

Chloroplasts are able to capture solar energy to perform photosynthesis. the reduction

of carbon dioxide to simple carbohydrates. This process entails a series of reactions

that result in the chemical splitting of water and the release of oxygen into the

environment. During the light phase, chlorophyll molecules absorb energy from light and

their electrons become energized. These excited electrons pass energy from one

chlorophyll molecule to another, resulting in the production of ATP and a special nucleic

acid-type carrier known as NADPH. This molecule carries the electrons to the next

stage of photosynthesis, the dark phase. The dark reactions manufacture sugars using

the energy stored during NADPH and ATP. The conversion of carbon dioxide present in

the atmosphere into carbon atoms in living organisms is called carbon fixation.

| |


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comprised

of six phases:





cell.






What is the controversy surrounding Bt corn and the monarch butterfly?

Share|

Bt corn was specifically engineered to control the European corn borer, which in 2003

caused an estimated $1 billion worth of damage to U.S. farmers. In 1999 a study was

released, based on controlled laboratory feeding experiments, that showed that corn

pollen from Bt-altered plants would kill monarch butterflies. In the study, threeday- old

monarch butterfly larvae were fed milkweed leaves dusted with Bt corn pollen. The

larvae ate less, grew slower, and had a higher mortality rate than those fed milkweed

with no corn pollen or milkweed coated with non-8t corn pollen. However, the laboratory

study did not provide information on the number of 8t pollen grains that were consumed

by the monarch larvae in order to observe the lethal effects. Also, no information was

provided on the effects on older, larger larvae, which would be expected to have a

higher tolerance to Bt toxicity. Headlines such as "Attack of the Killer Corn" and "Nature

at Risk" triggered regulatory action on the part of the European Union to ban the

importation and use of 8t corn varieties in Europe.

In response, other researchers described the use of 8t as a biocontrol agent since 1938

because of its selective toxicity to certain species within a given insect order. After

extensive studies dealing with the likelihood that 8t corn pollen would be found on

milkweed plants near cornfields that are close to the habitats of monarch butterflies,

safeguards were set to decrease the risk of Bt corn pollen to monarchs: 1) farmers in

monarch-rich areas should choose to grow 8t corn with [Lower toxicity levels; 2) plant a

border of 000-8t corn around a Bt cornfield to decrease the problem of pollen drift to

milkweed plants; and 3) plant milkweeds at sites away from cornfields to increase the

probability of female monarchs encountering milkweed plants that are uncontaminated

with corn pollen.

|


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| Biochemistry , Molecular Biology , Protein |

Amino acid sequence directs protein folding?

Share|

Question

Insulin possesses two polypeptide chains denoted A and B that are linked by disulfide

bonds. Upon denaturation by reduction of the SH groups of insulin, followed by

reoxidation, only 7% of the hormone activity is recovered. This is the level of activity

expected for random pairing of cysteine residues to form disulfide bonds. How can

these data be reconciled with the hypothesis that the amino acid sequence directs

protein folding?

Answer

Insulin is synthesized as preproinsulin that is proteolytically processed in the β cells of

the islets of Langerhans in the pancreas, to give proinsulin. After synthesis and folding,

a section of the molecule (the C peptide) is excised, leaving the A and B peptides

connected via disulfide bonds. Thus, native insulin, lacking the C peptide, lacks some of

the information necessary to direct the folding process.

| Protein |

Are humans the only animals who can think?

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Before one can answer this question, one must define what is meant by thought.

Thought can be defined in several ways: is it philosophical rumination or the processing

of perceptions of the natural world? Because we are still trying to translate animal

communication into human language, it is difficult to provide definitive proof of

philosophical thought processes. Current studies by animal behaviorists indicate that

animals that have a varied social life (such as chimpanzees) perceive the world in ways

similar to humans. However, since we do not share a common verbal language with

animals, it is impossible to know what they are thinking.

| Animal Behaviour , Evolution |

What is the significance of On the Origin of Species?

Share|

Charles Darwin (1809-1882) first proposed a theory of evolution based on natural

selection in his treatise On the Origin of Species. The publication of On the Origin of

Species ushered in a new era in our thinking about the nature of man. The intellectual

revolution it caused and the impact it had on man's concept of himself and the world

were greater than those caused by the works of Isaac Newton 0642-1727) and other

individuals. The effect was immediate-the first edition sold out on the day of publication

(November 24,1859). Origin has been referred to as "the book that shook the world."

Every modern discussion of man's future, the population explosion, the struggle for

existence, the purpose of man and the universe, and man's place in nature rests on

Darwin.

The work was a product of his analyses and interpretations of his findings from his

voyages on the HMS Beagle. In Darwin's day the prevailing explanation for organic

diversity was the story of creation in the book of Genesis in the Bible. Origin was the

first publication to present scientifically sound, well-organized evidence for the theory of

evolution. Darwin's theory was based on natural selection in which the best,or fittest,

individuals survive more often than those who are less fit. If there is a differ-450 ence in

the genetic endowment among these individuals that correlates with fitness,the species

will change over time and will eventually resemble more closely (as a group) the fittest

individuals. It is a two-step process: the first consists of the production of variation, and

the second, of the sorting of this variability by natural selection in which the favorable

variations tend to be preserved.

| Evolution |

Why is it so difficult for many people to accept the notion of evolution?

Share|

Evolution, as applied to the biological world, is in conflict with a literal interpretation of

the biblical story of creation described in Genesis. In the biblical account, each creature

was created separately by divine action and supposedly reproduces its own kind with

little change through the generations. In our own time, the scientific creationists contend

that a relative fixity of species is still a correct view and the earth’s span should be

measured in tens of thousands of years rather than the 4.6 billion years usually

accepted by the evolutionary biologists. For those who are oriented to fundamentalist

views, evolution becomes a challenge to religious convictions.

Most adherents to particular religious faiths have no problem reconciling their religious

convictions with an evolutionary perspective, but spiritual concerns did discourage many

at an earlier time. Darwin himself was concerned with how his espousal of evolution

would affect his wife’s pious sensibilities.

A second problem arises from the fact that evolution removes humans from the center

of the living world and ends the traditional separation of ‘‘lower’’ animals from ‘‘higher’’

humans. Humans have long been regarded as the goal and ultimate fulfillment of the

creative process. That humans are just one of many advanced groups that have arisen

from distant ancestors may be a blow to the collective ego of humankind.

An argument has been raised by some nonscientists that a belief in evolution may

encourage a dehumanization of shared social values. If we are merely highly evolved

animals, then perhaps the sanctity of human life may be ignored in the name of

expediency. Evolution may create a more permissive moral climate according to its

critics. At the same time, evolution’s immersion in continual change presents a

challenge to the stability of traditions that check our more aggressive tendencies.

Scientists do not generally accept these criticisms; they feel that the truths of science

are not instruments for directing human activity but are worthwhile in and of themselves.

The grandeur of life, which should inspire our conduct and concepts, is probably best

illuminated by the perspective of evolution.

| Evolution |

What are the major differences between apes and humans?

Share|

o The earliest difference, clearly encountered even in early forms of

australopithecines, is an upright posture and an efficient bipedalism (walking on the

hind legs) in humans. Associated with the erect posture is the tendency of the skull

to sit roughly centered atop the vertebral column. In apes, the column attaches to the

rear of the skull. In upright human forms, this repositioning of the skull provides

greater support for the cranium and encourages a straight vertical position for the

entire body.

o In apes, the big toe of the foot is long and opposable to the other toes. In all

members of Homo, the toe is smaller and is in line with the other toes. Although the

human foot is no longer readily prehensile, the five aligned toes provide a better

base support for the upright animal.

o Both the jaws and the teeth are considerably reduced in humans. This makes the

snout narrower. The lips are extremely motile and more readily serve such social

functions as speaking and kissing.

o The brow ridges of the ape are considerably reduced in humans. Instead, a smooth,

high forehead exists and is associated with extra cranial room for the forebrain.

o Closely associated with the increased brain size, especially in H. sapiens, was the

creation of a complex symbolic culture. Among the characteristics of that culture was

an elaborate toolmaking ability.

| Evolution

What is DNA origami?

Share|

DNA nanostructures in which a single long strand of DNA is folded so that it runs

through every double helix. The term is by analogy with the Japanese art of paper

folding in which a single sheet of paper is folded, without cuts, to create elaborate three-

dimensional shapes. Conceptually, there are two types of DNA origami. In single

stranded DNA origami, the structure is formed entirely by a single long strand and the

folding is due to interactions of the long strand with itself. In scaffolded DNA origami, the

folds are formed by the interaction of a long single strand and hundreds of short DNA

strands called “staples”. Single-stranded origami structures have the advantage of being

clonable, potentially exponentially reproducible like living things. So far, an almost-

single-stranded DNA octahedron with just five staples has been reported. Scaffolded

DNA origami structures have been easier to design and synthesize; a half dozen two-

dimensional shapes including a star, rectangle, triangle and smiley face, as well as a

threedimensional hexagonal tube have been reported. Scaffolded DNA origami

structures are easily connected to other nanoscale objects such as carbon nanotubes

and proteins, and might be used to organize them into complex nanocircuits or

nanofactories.

| Nanobiotechnology |

How the DNA nanoarchitecturing works?

Share|

DNA nanoarchitectures constructs that can be self-assembled from branched DNA

molecules. Their components may be simple branched species or more complex

structural motifs. Simple branched DNA junctions have been produced that contain 3–

12 double helices flanking a branch point. The species can be assembled and/ or

ligated into DNA stick polyhedra, where the edges are DNA double helices and the

vertices correspond to the branch points of the junctions. The first such molecule was a

DNA molecule with the connectivity of a cube. Other polyhedra produced to date include

a tetrahedron, an octahedron and a truncated octahedron. Branched junctions are

somewhat floppy, so only the branching and linking topologies of polyhedral are well

defined unless all the faces are triangles. Other individual objects that have been built

are topological targets, such as knots and Borromean rings. DNA is an ideal species to

use as a topological building block because a half-turn of DNA is equivalent to a node,

which is the fundamental topological feature of a knot or a catenane. The DNA double-

crossover (DX) molecule is another key element in DNA nanoarchitectures. This motif

consists of two helices joined twice by strands that connect them, leading to parallel

helix axes; the connection points are separated typically by Two-dimensional DNA

lattice. one and two double helical turns. Each of the connection points is a four-arm

junction, so the motif can be described as two four-arm junctions joined twice to each

other at adjacent arms. These are robust motifs, usually three to six double helical turns

in length and their structures can be reliably predicted. This system can be extended,

leading to molecules containing three or more helices joined laterally. Although most

often built to be roughly planar motifs, angles can be varied between pairs of helices,

using the helicity of DNA, e.g. a six-helix cyclic motif has been reported that

approximates a hexagonal tube (→DNA nanotubes). DX molecules and their relatives

can be exploited as tiles to produce two-dimensional crystalline arrangements by self-

assembly (→DNA self-assembly). An extra motif can be included in these tiles, visible

when the crystal is viewed in an atomic force microscope. The accompanying picture

shows how arrangements of two 16 × 4 nm tiles produce 32-nm stripes (top) or four tiles

produce 64-nm stripes (bottom). In addition to periodic arrangements, aperiodic patterns

can also be generated algorithmically. Single-stranded bacteriophages have been used

to produce greatly extended versions of the parallel DNA motif, capable of yielding

highly elaborate patterns, in a method called DNA origami. This is done by using the

bacteriophage genome (several thousand nucleotides) as a template to which a large

number of “staple strands” are added to fold the genome into a specific shape, including

holes in the middle; the addition of strands containing extra domains enable the

generation of further features. Smiley faces and a map of the western hemisphere are

examples of patterns generated by this method.

| Molecular Biology , Nanobiotechnology |

How does comparative biochemistry provide evidence for evolution?

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The evolutionary relationship between many organisms can be traced back to a

common ancestor. A common ancestor is an individual from which two or more related

species could have evolved. With the passage of time, organisms change and diverge

from their common ancestor to form new species. The following evidence for evolution

demonstrates the concept of the common ancestor. DNA, RNA, the genetic code and

protein synthesis are similar in all organisms. The greater the genetic and molecular

similarity between species, the closer their common ancestor. Humans and

chimpanzees have 98% of their genes in common. The remaining 2% is what

distinguishes these two species from each other. Humans did not descend from

chimpanzees but from primitive humans. However, at some point in evolutionary history,

primitive humans and primitive chimpanzees probably diverged from a common

ancestor. Diabetics can use insulin from cows and pigs because insulin from these

animals is almost identical to human insulin. In addition, hemoglobin in humans, which

has almost 600 amino acids, is almost identical to hemoglobin in all other vertebrates.

This similarity in chemical structure demonstrates that all vertebrates can be traced

back to a common ancestor.

| Ecology |

What are the strengths and weaknesses of an ecological perspective in understanding life?

Share|

The great strength of ecology is that it deals with living things in terms of their natural

surroundings rather than in artificial isolation. Other branches of biology focus upon

particular aspects of organisms and may thereby lose the reality of connections and

interrelationships that are vital to understanding life in its entirety. Ecology, by its very

nature of focusing on the context within which organisms develop and function, brings

together a variety of disciplines. Evolution, which provides a central structure in the

study of biology, can be fully appreciated only from

the ecological vantage point of populations interacting with their environment.Anatomy,

systematics, biochemistry, and even molecular biology becomemore fully focused when

utilized in analyses of ecosystems.Onamore practical level, the study of existing

ecosystems has vitalized the conservation movement and enhanced the active effort to

maintain ecosystems or even individual species of plants or animals threatened with

extinction. Apossible weakness of ecology stems from the broad spectrum of its

concerns—it tends to be diffuse. Individual ecologists do focus on particular aspects of

communities or the physical environment but the novice might find the field daunting by

its very breadth. In its descriptive phase, that breadth was more easily handled.The

recentemphasis on experimentation tends to encourage a specialization within the field

but experimentation introduces another problem. With experimentation, controlled

conditions may not be readily obtained in a field situation. Ecosystems can be studied

froma passive approach, in which the experimenter merely observes such phenomena

as energy flow, diversity of species, etc., but more ambitious attempts to establish an

ecological science require interventions that may be difficult to isolate and control.

Some success has been achieved, particularly where clear boundaries to a habitat

exist, such as on islands

| Ecology |


Share|

Creatine phosphate (CP) is a molecule stored in muscle that yields energy when the creatine splits from the attached phosphate. This energy is used to resynthesize the small amount of ATP (adenosine triphosphate) that is available to the muscle in the initial seconds of high intensity work (think 100-yard dash or a power lift). Because greater amounts of CP in the muscle can potentially allow for those high intensity efforts to be sustained a bit longer or to be performed more effectively, creatine supplementation has become popular within the last 15 years. Some research indicates that such supplementation can improve performance in the short term and in high intensity activities, but for more sustained activities it has little or no effect because of the ATP’s great dependence on aerobic metabolism. The long-term effect of such supplementation on the human body is unknown.



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What is triclosan?

Share|

Triclosan has properties of a phenol and is extremely popular in antibacterial products

such as hand sanitizers, antibacterial soaps, lotions, toothpastes, and even as an

antimicrobial additive in plastics. Resistance to triclosan occurs in some bacterial

species, and there is concern that resistance to triclosan may provide cross- resistance

to antibiotics. This is of particular concern with antibiotic resistant strains of

Staphylococcus aureus.

| Pharmacology |

How did scientists decide that DNA was the genetic material for all cellular organisms?

Share|

The proof that the material basis for a gene is DNA came from the work of Oswald

T.Avery (1877-1955), Colin M. MacLeod (1909-1972), and Maclyn McCarty (1911-) in a

paper published in 1944. This group of scientists followed the work of Griffith in order to

discover what causes nonlethal bacteria to transform to a lethal strain. Using specific

enzymes, all parts of the S (lethal) bacteria were degraded, including the sugar like

coat, the proteins, and the RNA. The degradation of these substances by enzymes did

not affect the transformation process. Finally, when the lethal bacteria were exposed to

DNase, an enzyme that destroys DNA, all transformation activity ceased. The

transforming factor was DNA.

| |

Can we make artificial cells?

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Research in progress at the National Aeronautical and Space Administration (NASA) is

focused on artificial cells as a means to deliver medicine in outer space; these cells are

able to withstand dehydration and thus can be safely stored for long periods. Artificial

cells are made of a polymer that acts like a cell membrane, but the polymer is stronger

and more manageable than real membranes. These polymers are called polymersomes

and can be made to cross-link with other polymers. Researchers feel that many different

kinds of molecules can be encapsulated within these polymersomes and then delivered

to specific target organs. An example would be an artificial blood cell that not only

delivers oxygen but also medication as it travels through the body.


How do brain cells store memories?

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The part of your brain responsible for processing memory is the hippocampus. It is

believed that memories are formed at the level of individual nerve cells. The synapse is

the point at which adjoining nerve cells touch. and it is this juncture that is the building

block of memory systems. Information moves across the synapse-the information signal

is carried inside a cell by a second messenger (known as CAMP), which then activates

other cell machinery. The end result is the switching on of a gene that regulates

memory. The product of the gene, a protein, promotes synaptic growth and can convert

short term memory to long term memory.

| cell signaling |


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excision repair












methyltransferase














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comprised

of six phases:





cell.






| cell signaling |

What is the structural basis of activation of heterotrimeric G proteins?

Share|

Heterotrimeric G proteins are composed of α, β, and γ polypeptide chains. Usually, the

α and γ chains are anchored to the inner leaflet of the plasma membrane by lipid

anchors that consist of a fatty acid that is linked to a cysteine side chain by a thioester

bond. , the binding of a signaling ligand leads to exchange of a molecule of GDP for a

molecule of GTP, bound to the Gα subunit. Concurrently, the Gα subunit dissociates

from the GβGγ subunit. This allows both the Gα and the GβGγ subunits to interact with

other signaling molecules.There are multiple copies of the genes for the Gα, Gβ, and

Gγ polypeptides in eukaryotic genomes. In the human genome there are at least 15

different Gα subunits, 5 Gβ subunits, and 10 Gγ subunits. Hence, there are potentially

~1000 different combinations of these subunits, with different possible physiological

effects that depend on which G protein-coupled receptor(s) they become associated.

| cell signaling

A simple overview of Cancer and Malignant growth

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Cancer is a disease of the body’s cells. It occurs when cells in the body become

abnormal and grow out of control. A change which makes the gene faulty is called a

mutation. Some special genes, called control genes, instruct the cell to copy its genes

correctly, and to divide in an orderly manner. They stop controlling cell division, which is

cancer.

Benign Tumors: Tumors arise with great frequency, especially in older animals and

humans, but most pose little risk to their host because they are localized and of small

size. The surface interaction molecules that hold tissues together keep benign tumor

cells, like normal cells, localized to appropriate tissues. A fibrous capsule usually

delineates the extent of a benign tumor.

Malignant tumor: In contrast, the cells composing a malignant tumor, or cancer,

express some proteins characteristic of the cell type from which it arose, and a high

fraction of the cells grow and divide more rapidly than normal. Some malignant tumors

remain localized and encapsulated, at least for a time; an example is carcinoma in situ

in the ovary or breast. Most, however, do not remain in their original site; instead, they

invade surrounding tissues, get into the body’s circulatory system, and set up areas of

proliferation away from the site of their original appearance. The spread of tumor cells

and establishment of secondary areas of growth is called metastasis; most malignant

cells eventually acquire the ability to metastasize. Thus the major characteristics that

differentiate metastatic (or malignant) tumors from benign ones are their invasiveness

and spread. They are usually less well differentiated than normal cells or benign tumor

cells. The presence of invading cells is the most diagnostic indication of a malignancy.

Cancer cells can multiply in the absence of growth-promoting factors required for

proliferation of normal cells and are resistant to signals that normally program cell death

(apoptosis). Both primary and secondary tumors require angiogenesis, the recruitment

of new blood vessels, in order to grow to a large mass. Cancer cells, which are closer in

their properties to stem cells than to more mature differentiated cell types, usually arise

from stem cells and other proliferating cells.

Following are the types of Cancer:

1. Carcinoma: It includes tumors of brain, breast, skin, cervical region. These are

derived from epithelial tissue, originating from either ectoderm or endoderm. These

occurs as solid tumors, located in the nervous tissue on the body surface or associated

glands.

2. Sarcoma: They are the cancers of connective tissues, cartilage, bone or muscles

which are mesodermal in origin.

3. The leukemias: A class of sarcomas, grow as individual cells in the blood, whereas

most other tumors are solid masses. (The name leukemia is derived from the Latin for

“white blood”: the massive proliferation of leukemic cells can cause a patient’s blood to

appear milky)

4. Lymphoma: Lymph nodes, bone marrow, liver and spleen produces excessive

lymphocytes. Cancer in them are called as lymphomas eg. Hodgkin’s disease.

| Cancer Biology |

Fructose intolerance - Why is it life-threatening?

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Question

An inborn error of liver fructose-1-phosphate aldolase (aldolase B) leads to a condition

known as fructose intolerance. The condition is characterized by life-threatening liver

damage that can occur after consuming fructose in the diet. Why is it life-threatening?

Answer

Fructokinase catalyzes the formation of fructose 1-phosphate from fructose and ATP. It

is a very rapid reaction that has minimal product inhibition by fructose 1-phosphate.

Normally, fructose 1-phosphate enters glycolysis after aldolase B has catalyzed its

scission to yield glyceraldehyde and dihydroxyacetone phosphate; then

dihydroxyacetone phosphate passes via triosephosphate isomerase to glyceraldehyde

3-phosphate and then into the final part of glycolysis, generating pyruvate. This

pyruvate leads to regeneration of ATP. If aldolase B is inactive, then phosphate

becomes trapped in fructose 1-phosphate which seriously compromises ATP

regeneration. As a result, ATP concentrations in the liver fall dramatically, leading to a

failure of the many ATP-dependent reactions including those that pump ions across the

plasma membrane. This leads to irreversible damage of the hepatocytes. Even in

normal individuals, the activity of aldolase B is sometimes a little lower than that of

fructokinase so, in general, ingesting large doses of fructose is not advisable.

| Metabolism

Why do many marine fish drink seawater, whereas freshwater fish do not drink at all?

Share|

Marine fish, living in a hypertonic environment, suffer from a shortage of available water.

They drink seawater and extract the water from the salt solution for their metabolic

needs. However, they are left with excess salts, which must then be excreted. This is

largely accomplished through glands in the gills that excrete NaCl. A variety of ATPases

participate in the reaction, which is highly endergonic. In some marine fish, special

rectal glands excrete excess salts into the terminus of the digestive tract, where they

pass into the external environment.

Since freshwater fish are surrounded by a hypotonic environment, their problem is quite

different. They must get rid of the fresh water that is constantly moving into their bodies.

To drink water would be counterproductive, and so they never drink. Instead, the little

salt that is present in the water around them is drawn in across the gills. This process

also requires energy and involves the participation of ATP-splitting enzymes in glands

within the gill.

| zoology |

| Genetics |

What is an example of gene control?

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An elegant example of gene control in bacteria is the operon system. A cluster of genes

that is responsible for synthesizing a particular protein is called an operon. This cluster

of genes typically includes a promoter region, an operator gene, a regulatory gene, and

a number of structural genes that actually encode the protein. Operon systems can be

inducible (meaning they are normally “off ”) or repressible (meaning they are normally

“on”).


Is a gene the same as a DNA molecule?

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Genes are the units of heredity. A gene is a segment or section of a DNA molecule.

This segment of DNA provides a genetic code for the synthesis of proteins. The nucleic

acid language of the gene is written as a sequence of bases on the DNA molecule.

Such a sequence might read G- C- T- T- A- C- C- G- A- T- T. . . . This is the molecular

“language” that will ultimately specify an amino acid sequence in a protein.


What are the features of hnRNA?

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Heterogeneous nuclear RNA (hnRNA)- The primary precursor mRNA transcript made in

the eukaryotic nucleus are called "hnRNA," an abbreviation for "heterogeneous nuclear

RNA. Features are as follows:

Introns: Since many eukaryotic nuclear genes are interrupted by introns, RNA

transcripts of intron-containing genes have intronic RNA sequences.

Poly A tails at the 3'-end: Poly A tails added to the 3'-end of most, but not all hnRNAs

during nuclear RNA processing. These tails are retained in the processed mRNA.

5'-Cap structure: A modified GTP is covalently attached to the 5'-end of most precursors

to mRNA. This cap structure is also retained in the processed mRNA.

Base Composition and relation to template strand: RNA is synthesized from a DNA

template. The sequence of the RNA is complementary to the DNA template strand, and

opposite in polarity. C and T in the DNA template are transcribed by RNA polymerase

as G and A in the hnRNA, respectively. A and G in the DNA template are transcribed as

U and C in hnRNA. Thus hnRNA and mRNA are sequences of A, G, C and U's.


How DNA-RNA hybridization occurs

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Both DNA and RNA are able to form hybrids in solution with other DNA or RNA

molecules that have complementary base pairing. Double-stranded DNA can be

"denatured" by heating to high temperature. If the resulting single-stranded DNAs are

slowly cooled, the separated DNA strands can reanneal to reform the DNA duplex.

Notice that A pairs with T and G pairs with C when a DNA strand hybridizes with

another DNA strand. An RNA molecule can also form a base-paired DNA-RNA duplex

molecule with a DNA that has complementary base pairing. The most common source

of DNA complementary to an mRNA is the DNA coding strand that was the template for

synthesis of the RNA. In DNA-RNA hybrid formation, G base pairs with C, A of the RNA

pairs with T of the DNA, and U or the RNA pairs with A of the DNA.


What is self-catalytic RNAs?

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Ribozymes - The term "ribozyme" was originally suggested by Thomas R. Cech, Nobel

Prize winning biochemist, who first discovered this class of RNA molecules. A ribozyme

is an RNA molecule that can catalyze a biochemical reaction. Prior to the discovery of

ribozymes, it was generally assumed that protein enzymes were the only class of

biological catalysts. Cech's discovery was truly revolutionary in upsetting this dogma.

The first ribozymes discovered were introns that could catalyze their own splicing, i.e. a

special type of intron within a pre-RNA molecule was found to catalyze all steps needed

for intron removal and joining of the exons together at the biologically correct site.

Ribozymes with other types of biological activity have since been discovered. One

intriguing potential ribozyme is the peptidyl transferase activity of the ribosome. Many

believe that peptide bond formation is catalyzed by the 23S ribosomal RNA, a potential

ribozyme, rather than ribosomal proteins.


What information can a forensic scientist determine from a human hair?

Share|

A single strand of human hair can identify the age and sex of the owner, drugs and

narcotics the individual has used (up to 90 days previously), and, through DNA

evaluation and sample comparisons, from whose head the hair came.

| Genetics , Technology |


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wine fermentation.






research.



What is cosmid?

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Genetically engineered vector containing phage and plasmid genetic elements which

accepts inserts of larger length (average of 45 kb) than phage (15 kb) or plasmid (1–10

kb) derived vectors. The replication origin and antibiotic resistance gene come from

plasmids. The cos sites required for packaging come from phages. Cosmids are

packaged into capsids and are able to infect host cells, thus efficiently injecting the

vector DNA which is then amplified and maintained as a giant plasmid in the host cell.

| Genetics |

What is Barr body Genes?

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Located inside the nuclear envelope, it is a densely staining object that is an inactivated

X chromosome in female mammalian cells. Most Barr body genes are not expressed.

They are reactivated in gonadal cells that undergo meiosis to form gametes. Female

mammals are a mosaic of two types of cells, those with an active maternal X and those

with an active paternal X. Which of the two Xs will be inactivated is determined

randomly in embryonic cells. After an X is inactivated, all mitotic descendants will have

the same inactive X. As a consequence, if a female is heterozygous for a sex-linked

trait, about half of her cells will express one allele and the other cells well express the

alternate allele. Examples of this type of mosaicism are coloration in calico cats and

normal sweat gland development in humans. A woman who is heterozygous for this trait

has patches of normal skin and patches of skin lacking sweat glands. X chromosome

inactivation is associated with DNA methylation. Methyl groups (-CH3) attach to

cytosine, one of DNA’s nitrogenous bases. Barr bodies are highly methylated compared

to actively transcribed DNA.

What determines which of the two X chromosomes will be methylated? – A recently

discovered gene, XIST is active only on the Barr body. The product of the XIST gene,

X-inactive specific transcript, is an RNA; multiple copies of XIST attach to the X

chromosome inactivating it.


How Genes can be exchanged between chromatids?

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When two homologous chromosomes physically exchange corresponding segments

during prophase I of meiosis, geneticists call it crossing over. Recombinations occur at

chiasmata during pachytene of meiosis-I. If just a few exchanges occur, genes that are

closer together tend to stay together. The farther apart on the same chromosome genes

are, the more likely they will separate during recombination. The two extremes are

independent assortment and complete or absolute linkage. The progeny resulting from

crossing over appear in repeatable proportions, called the recombinant frequency.

Greater recombination frequencies are observed for genes that are farther apart on the

chromosomes because a chiasma is more likely to cut between genes that are far apart

than genes that are closer together.


Are chromosomes the only parts of bacteria that can be transformed?

Share|

Bacteria possess extrachromosomal loops of DNA called plasmids. Plasmids are small,

self-replicating loops of DNA with about 10 to 50 genes. They are not essential for the

survival of the bacterium. New segments of DNA acquired in transformation may attach

to the plasmids of a bacterium, or entire plasmids may be recovered from the local

environment. Additionally, plasmids can sometimes be lost in a process called curing,

which can occur spontaneously or can be induced by certain environmental factors.

| Genetics , Microbiology |

Abnormalities in chromosome number give rise to diseases of karyotype. How might these aberrations occur?

Share|

Under usual conditions of meiotic division, each tetrad separates into its constituent

homologous chromosomes. One homologue migrates to one pole and the other

homologue to the opposite pole during anaphase of the first meiotic division. If this

separation does not occur, all the tetrads may move to one pole, while the opposite pole

may receive no chromosomes at all. This would eventually produce diploid cells as

gametes (in those organisms in which meiosis is involved in gamete formation). Should

such a diploid gamete unite with a more typical haploid gamete, a zygote would be

produced with three sets of chromosomes, a triploid individual. In

plants, the formation of triploid and even higher orders of polyploidy represents a

mechanism for producing new species of the organism in the course of evolution. This

alteration of ploidy is less common in animals.

More commonly, a single tetrad will fail to separate into its constituent chromosomes.

This will eventually result in gametes that have a double dose of one chromosome and

others that have no representative for that particular chromosome. In Down’s syndrome,

a sperm or egg with two chromosomes 21 unites with a normal haploid sperm or egg to

produce a zygote with three such chromosomes. The failure of tetrads to disjoin is

called nondisjunction, and disorders arising from the phenomenon are known as

diseases of nondisjunction. They include Down’s, Klinefelter’s (XXY male genotype),

and Turner’s (XO, i.e., having only one X chromosome,female genotype) syndromes.

Fragmentaton, deletion, and internal inversion of chromosomes or chromosome parts

may also produce diseases of karyotype.

| Genetics |

| Cell biology |

Are prokaryotes and eukaryotes similar in any respects?

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Prokaryotes and eukaryotes share common features, among them the possession of

nucleic acids and other organic substances such as proteins, carbohydrates, and lipids.

In addition, they utilize similar metabolic reactions such as glycolysis and chemiosmosis

for the utilization of food and the production of energy and waste. Also, they exhibit

many of the same physiological features such as motion and reproduction, although the

mode of reproduction may be different and different organs of motility may exist.

| Biochemistry , cell biology |


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comprised

of six phases:





cell.







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wine fermentation.






research.



Will growth factors can stimulate cells to divide?

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Cyclin-Cdk complexes provide internal control for cell cycle decisions. Cells in

multicellular organisms must divide only when appropriate. They must respond to

external signals, controls called growth factors.

Some cells respond to growth factors provided by other cells.

• Platelets release platelet-derived growth factor, which diffuses to the surface of

Cells to stimulate wound healing.

• Interleukins are released from one type of blood cell to stimulate division of

another type resulting in body immune system defenses.

• The cells of the kidney make erythropoietin, which stimulates bone marrow

Cells to divide and differentiate into red blood cells.

Cancer cells cycle inappropriately because they either make their own growth factors

Or no longer require them to start cycling.

| cell biology |

Are viruses alive?

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In terms of the definition of life viruses are not alive. They are complex associations of

two macromolecules—protein and nucleic acid—but they are neither self-regulating nor

capable of metabolism. Perhaps most crucial is their inability to reproduce

independently. They may be crystallized and kept in an inert state in test tubes for long

periods of time. Their talent lies in their ability to seduce living cells into manufacturing

new viral material following the injection of viral nucleic acid into those cells. The genetic

message of the virus literally captures the protein-synthesizing machinery of the cell

which then carries out the bidding of the viral information tape. The cell also produces

the nucleic acids required for viral replication. At one time, viruses were felt to be links in

the stepwise increasing complexity of macromolecules on their journey toward

becoming full-fledged cells. The more likely explanation offered by many virologists at

this time is that viruses are degenerate products of more complex forms, even of once-

living cells.

Forms resembling living organisms exist that are even simpler than viruses. In 1971, a

scientist at the U.S.Department of Agriculture showed that infections of potato plants

are caused by very small bits of circular RNA lacking a protein coat. These tiny lengths

of naked RNA, soon found to cause a variety of diseases in flowering plants, were

called viroids by their discoverer, T. O. Diener. Although viroids cause disease, they do

not destroy the cells they parasitize. The mechanisms whereby they enter the cell and

take over part of its polynucleotide synthesizing machinery are not fully known.

Several neurological diseases, including scrapie in sheep, arise from an infestation of

central nervous system cells by a self-replicating protein called a priori. Prions have

been isolated from diseased tissues but their mode of action and reproductive strategy

are unknown.

| cell biology |

Are plasma membranes the outer boundaries of all cells?

Share|

No, in many cells the plasma membrane is encased within an extraneous coat of

nonliving material that usually confers some rigidity on the cell it surrounds. Although

not affecting permeability, this rigid coat affords considerable protection to the

underlying cell, especially in dilute solutions in which the cell might take in water and

tend to swell.The coat is known as a cell wall in plant cells, fungi, and bacteria. Thiswall

is composed of cellulose in all plant cells. Cellulose is the major component of wood

and certain other commercially useful plant products. In fungi,the walls are composed of

chitin, a complex carbohydrate rich in amino-containing sugars. Bacterial cell walls

consistof complex carbohydrates and linked short peptides, but there is considerable

variation in the chemical makeup of these mixed polysaccharide and amino acid chains

in different bacterial strains.

In most animal cells, theremaybe a layer of carbohydrate lying outside the

plasmamembrane, but this is not a separable coat. It is called a glycocalyx and exists in

intimate association with the membrane. The carbohydrates themselves are

generally short chains but are covalently bound to the lipids or proteins of the

membrane to produce a thin, furlike cover for the cell. The glycocalyx contains receptors

for a variety of substances with which the cell may interact. The blood types of humans

are based on the antigenic properties of the glycocalyx of the red blood cell. The sites

on many cells that signal ‘‘self’’ or ‘‘foreigner’’ to the immune systemof host organisms

occur within the glycocalyx as well. Thus, in dealing with the possibility of whether a

transplanted tissue or organ will be rejected, a major focus is on the glycoproteins

formed within the glycocalyx. Collectively, the chief set of such glycoproteins is known

as the major histocompatibility antigens, and these antigens are coded for by a group of

genes known as the major histocompatibility complex (MHC).

In many cells, special structures are formed that anchor the cells firmly together. These

structures, particularly associated with epithelial tissue, include tight junctions, inwhich

there is virtually no intercellular space, and desmosomes,

in which a highly layered, narrow space can be discerned. Such structures may also

play a role in the transport of materials from one cell to another. Animal cells involved in

absorption, such as the cells that line the intestine, often have filaments extending out

from the plasma membrane. These filaments, which are rich in carbohydrates, are

known as microvilli. They increase the absorptive surface of the cell and may also

contain enzymes that function in digestion. Another type of extracellular coat is formed

by the layers of polysaccharide that surround the eggs of many vertebrate and

invertebrate species. These coats, usually added to the egg proper as it passes along

the reproductive tract before hatching, must be penetrated by the sperm at the time of

fertilization. The enzymes associated with the acrosome found in the head of most

sperm cells aid in carrying out this task.Among many protista, a highly elastic pellicle

overlies the plasma membrane, but the function of this structure is not completely clear.

In Euglena, it consists of flexible protein strips.

| cell biology |

| Microbiology |


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What is the general course of development for cases of syphilis?

Share|

The etiologic agent of syphilis is the spirochete Treponema pallidum. The organism is

motile and can be observed moving about under the dark- field microscope. It is

extremely difficult to cultivate in the laboratory, and direct observation is usually required

for diagnosis. The organism is transmitted among humans by sexual contact, such as

during sexual intercourse.

The development of syphilis is generally an involved series of events. The primary stage

consists of a painless, hard sore called a chancre at the site where spirochetes have

entered the body(usually on the external or internal genital organs). After several

weeks, the chancre disappears and a latent period ensues. The secondary stage

appears many weeks or months later. The secondary stage is accompanied by a skin

rash with pustular lesions and skin eruptions. The hair on the head and eyebrows is

often lost. Liver inflammation is common, and an influenza like syndrome may appear.

The person is highly contagious at this point. After some time, the lesions heal and

another latent stage develops. A tertiary stage may appear years later. This stage is

characterized by the formation of gummas, which are gummy, granular lesions that

form in the brain and major blood vessels. The patient often becomes paralyzed and

usually suffers permanent damage to the blood vessels. In addition, the symptoms of

dementia may occur. Death usually accompanies destruction of the heart and blood

vessel tissues.

One of the dangers of syphilis is the possible development of congenital syphilis. In this

instance, the spirochetes cross the placenta and enter the fetal blood from the mother’s

blood. Newborns show signs such as notched incisors (Hutchinson’s teeth), a

perforated palate, an aged- looking face, and damage to the nose. Congenital syphilis

may also result in stillbirth.

| Gynacology , Microbiology |


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soon as weeks after infection or as long as 20 years or more after infection.

| Immunology , Microbiology |

Are chromosomes the only parts of bacteria that can be transformed?

Share|

Bacteria possess extrachromosomal loops of DNA called plasmids. Plasmids are small,

self-replicating loops of DNA with about 10 to 50 genes. They are not essential for the

survival of the bacterium. New segments of DNA acquired in transformation may attach

to the plasmids of a bacterium, or entire plasmids may be recovered from the local

environment. Additionally, plasmids can sometimes be lost in a process called curing,

which can occur spontaneously or can be induced by certain environmental factors.

| Genetics , Microbiology |

Are there any unique ways that humans derive benefits from microorganisms?

Share|

Humans derive substantial benefits from the activities of microorganisms. For example,

many microbial species live in and on various parts of the body and prevent pathogenic

bacteria from gaining a foothold. These organisms are referred to as normal flora.

Microorganisms produce many of the foods we eat, including fermented dairy products

(sour cream, yogurt, and buttermilk), as well as fermented foods such as pickles,

sauerkraut, breads, and alcoholic beverages. In industrial corporations, microbes are

cultivated in huge quantities and used to produce vitamins, enzymes, organic acids, and

other essential growth factors.

| Microbiology |


Share|






resistance. They






Are bacteria able to move, and, if so, how?

Share|

Bacteria (and other prokaryotes) have the ability to move by means of flagella. Flagella

are composed of the globular protein flagellin. They are extremely long and thin and

cannot be seen by the light microscope unless specially stained. They are, however,

readily visible under the electron microscope. Bacterial flagella propel the organism by a

rotary motion. Each flagellum has three basic parts: the filament, which is the long,

outermost region containing the flagellin; the hook, which is composed of a different

protein and lies at the proximal end of the filament; and the basal body, which anchors

the filament to the cell membrane and cell wall and is composed of a series of rings

encircling a central, small rod (Gram- positive bacteria have only an inner pair of rings,

while Gram- negative bacteria have both inner and outer pairs of rings).

| cell structure , Microbiology |

How do microorganisms influence the carbon cycle on Earth?

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Most of the organic matter present in soil originates in plant material from leaves, rotting

trees, decaying roots, and other tissues. In the carbon cycle, soil bacteria and fungi

recycle this carbon by using the organic matter in their metabolism. Without the

recycling action of these organisms, life would suffer an irreversible decline as the

nutrients essential for life became tied up in complex molecules.

| Microbiology |

Which microorganisms are involved in the pickling process in food production?

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In the pickling process, microorganisms grow and ferment the food in a salty

environment while producing large amounts of acid from available carbohydrates.

Species of Leuconostoc and Lactobacillus are commonly used in the pickling process.

To produce sauerkraut, cabbage is grated and salted and allowed to ferment naturally

(since the bacteria are already present among the leaves). For pickled cucumbers, salt

is added to fresh cucumbers, and the naturally occurring bacteria ferment the vegetable

carbohydrates over a period of weeks. Different spices are added to prepare various

forms of sauerkraut and pickled cucumbers.

| Microbiology |

Do all bacteria require oxygen for growth?

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Many bacteria are aerobic; that is, they require oxygen to grow and perform the

biochemical reactions of their metabolism. There are, however, a large number of

bacterial species that are anaerobic and are cultivated in a special apparatus where the

oxygen has been removed. These bacteria (known as anaerobes) live in the absence of

oxygen, and they are found in the muddy bottom of swamps, landfills, and soil. Some

anaerobes are obligate anaerobes, while others are facultative anaerobes, meaning that

they live with or without

oxygen.

| Microbiology |

Which bacterium is responsible for tuberculosis, and what are the characteristics of the organism?

Share|

Tuberculosis is caused by a slender rod known as Mycobacterium tuberculosis. This

slow- growing rod is neither Gram- positive nor Gram- negative; rather, it is acid- fast.

When stained with carbolfuchsin, steam must be used to force the stain through the

bacterial cell wall. Once stained, however, the organism cannot be decolorized even if

dilute acid- alcohol is used. This acid- fast characteristic is due to the presence of a very

thick cell wall containing mycolic acid.

| Microbiology |

Why is microbial control necessary and what are some of the factors that go into the choice of a particular antimicrobial agent?

Share|

The control of microorganisms is an important way of preventing pathogens from

reaching the body.Sterilizing laboratory equipment, hospital supplies, and industrial

apparatus helps contain contamination.The choice of a particular antimicrobial agent

depends on such things as the kind of material to be treated(living or nonliving), the kind

of croorganism to be controlled, the environmental conditions existing at the time of the

agent’s use (for example, the temperature of the environment and concentration of

microorganisms),

the acidity or alkalinity of the area, and the presence of organic matter.

| Microbiology |

What is the advantage of the attenuated viruses in a vaccine?

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Attenuated viruses can be taken orally because they will survive passage into the

gastrointestinal tract and will be absorbed into the blood stream. The method of

administration is therefore easier than by injection.However, the drawback is that the

viruses may on certain occasion induce mild symptoms of disease in the body and they

pose more of a risk than the inactivated viruses. They do call forth a more substantial

immune response, however, and for this reason they may be advantageous when an

epidemic is taking place or is anticipated.

| Microbiology |

How is the Gram stain procedure performed in the microbiology laboratory?

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In the laboratory, a heat- fixed smear of bacteria is stained with crystal violet for one

minute. Then, iodine,which acts as a mordant, is added to the smear for one minute,

and the remainder is washed free. All bacteria are now blue- purple. Alcohol decolorizer

is added to the slide until the free stain is removed. In this step, the Gram- negative

bacteria lose the blue- purple dye, but Gram- positive bacteria retain the dye and remain

blue- purple. In the fourth step, the red dye safranin is added to the smear. The Gram-

negative bacteria will accept the dye and become red- pink, while the Gram- positive

bacteria remain blue- purple. At the conclusion of the procedure, the stains are

examined under the microscope and the color of the bacteria reveals the Gram reaction.

| Microbiology |

Why is tetanus considered a disease of the nervous system?

Share|

Tetanus is a disease caused by a Gram- positive, spore- forming anaerobic rod called

Clostridium tetani.This organism often exists in the spore form in the human and animal

intestine and passes to the soil inthe feces. Tetanus is usually acquired by puncture of

the skin from a wound with a piece of glass or other pointed object. The etiological

agent grows in the dead tissue and produces a number of toxins, which have their effect

on this tissue. These toxins prevent the destruction of acetylcholine in the synapse and

encourage nerve impulses to pass into the muscles, where they cause continual muscle

contractions symptomatic of tetanus. Since the primary effect is in the nervous system,

tetanus is considered a disease of this

system.

| Microbiology |

| cell structure |


Share|



comprised

of six phases:





cell.







Share|






resistance. They






Are bacteria able to move, and, if so, how?

Share|

Bacteria (and other prokaryotes) have the ability to move by means of flagella. Flagella

are composed of the globular protein flagellin. They are extremely long and thin and

cannot be seen by the light microscope unless specially stained. They are, however,

readily visible under the electron microscope. Bacterial flagella propel the organism by a

rotary motion. Each flagellum has three basic parts: the filament, which is the long,

outermost region containing the flagellin; the hook, which is composed of a different

protein and lies at the proximal end of the filament; and the basal body, which anchors

the filament to the cell membrane and cell wall and is composed of a series of rings

encircling a central, small rod (Gram- positive bacteria have only an inner pair of rings,

while Gram- negative bacteria have both inner and outer pairs of rings).

| cell structure , Microbiology |

Down syndrome - what might it be?

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Question

In some sufferers of Down syndrome, the somatic cell nuclei do not contain three

chromosomes number 21.There is a chromosomal defect relating to chromosome

number 21; what might it be?

Answer

A fragment, usually the short arm, of chromosome 21 is translocated onto another

chromosome; thus, there are three copies of a fragment of the short arm in any one cell.

This is a relatively rare occurrence.

| cell structure |

Mitochondria - what might be the significance of having such a complex membranous structure?

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Question

Given that mitochondria do not have the same aggressive autolytic capacity as

lysosomes, what might be the significance of having such a complex membranous

structure? After all, the endoplasmic reticulum and the plasma membrane could

potentially support those enzymes found in mitochondrial membranes.

Answer

In fact, bacteria do not have mitochondria, but some types do have membranous

intrusions into the cytoplasm called mesosomes. These are similar in function to the

inner membrane of mitochondria .The reason mitochondria are distinct from other

membranous structures in higher cells is possibly due to their evolutionary origin as

intracellular symbionts and to the fact that the spatial separations of functions lead to

more advantageous (in terms of natural selection and selective advantage) control of

the various metabolic processes that are now

distributed between distinct compartments.

| cell structure |

what is the primary source of mitochondrial DNA?

Share|

Question:

(a) From what primary source is the DNA in your mitochondria, your mother or your

father? (b) Speculate onpossible inheritance patterns if there were a defect in one or the

other parent’s mitochondria.

Answer:

(a) Mother.

(b) If a defect exists in a mitochondrial gene, all progeny from that female will carry the

defect.

Several well-defined diseases resulting from such a defect have been described.

| cell structure |

What might be the consequence and role of compartmentation of enzymes?

Share|

Question:

There are two forms of the enzyme carbamyl phosphate synthetase, one in the

mitochondrial matrix and the other in the cytoplasm. What might be the consequence

and role of this compartmentation of enzymes?

Answer:

It enables separate control over the rates of urea and pyrimidine synthesis

| cell structure |

Microsomes - From where do they arise?

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Question:

Microsomes are small spherical membranous vesicles with attached ribosomes. They

sediment, during differential sedimentation, only in the late stages of a preparation when

very high centrifugal velocities are used. They don’t appear in electronmicrographs of a

cell. From where do they arise?

Answer:

Fragments of endoplasmic reticulum are transformed from lipid bilayer sheets, with

attached ribosomes, into spherical vesicles. This is a result of the homogenization used

in preparing the samples and also the tendency of lipid bilayers to spontaneously

reseal.

| cell structure |

What is the biochemical basis of this test?

Share|

Question:

A commonly used test of the viability of cells in tissue culture is whether or not they

exclude a supravital dye such as toluidine blue. If the cells exclude the dye, they are

considered to be viable. What is the biochemical basis of this test?

Answer:

The membranes of all living cells are selectively permeable to ions and other chemical

species. This selectivity is in many cases linked to the supply of ATP, and one feature of

cell death is a low concentration of ATP. In this state, the cell no longer excludes foreign

compounds, such as toluidine dye.

| cell structure |

PAS staining of microscope sections of red blood cells gives ?

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Question:PAS staining of microscope sections of red blood cells gives a pink stain on

only one side of the cell membrane. Which side is it, the extracellular or the intracellular

side?

Answer:Extracellular. All glycoprotein and glycolipids of the plasma membrane of red

and all other cells are on theoutside of the cell. No oligosaccharides are present on the

inner face of the cell membrane.

| cell structure |

How many red blood cells are produced in an average 70-kg person every second?

Share|

The number is 2.5 million! The average life span of a human red cell is 120 days;

therefore the number produced per second is simply given by the 26 trillion (average

cells in 70kg person), divided by 120 days and expressed in seconds.

| cell structure |

How many red blood cells are there in an average 70-kg person?

Share|

There are ∼2.6 × 1013, or 26 trillion. The total blood volume is ∼5.5 L, and ~40% of that

is red blood cells;i.e., there are ~2.2 L of red cells. Since each cell has a volume of ∼86

× 10−15 L , the result follows from dividing 2.2 L by this number.

| cell structure |

A person’s lysosomes lack the enzyme β-glucosidase ????

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Question: There is an inherited disease in which a person’s lysosomes lack the

enzyme β-glucosidase What are the clinical and biochemical consequences of this

deficiency?

Answer:The disease is called Gaucher disease, and it is the most common of the

sphingolipidoses; its incidence in the general population is ∼1:2500. This class of

disease results from defective hydrolysis of membranecomponents, sphingolipids , that

are normally turned over in the cell by hydrolytic breakdown inthe lysosomes. The

sphingolipids are lipid molecules with attached carbohydrate groups. A failure to beable

to remove glucose from these molecules results in their accumulation in the lysosomes.

In fact, over a few years, the cells which have rapid membrane turnover, such as the

liver and spleen, become engorgedwith this lipid breakdown product. Clinically the

patients have a large liver and spleen and may show signs of mental deterioration if

much of the lipid accumulates in the brain as well.

| cell structure |

How may cells be disrupted in order to obtain subcellular organelles by centrifugal fractionation?

Share|

There are several ways of disrupting cells:

1. Osmotic lysis. The plasma membranes of cells are water-permeable but are

impermeable to large molecules and some ions. Thus if cells are placed into water or

dilute buffer, they swell due to the osmotically driven influx of water. Since the plasma

membrane is not able to stretch very much (the red cell membrane can only stretch by

up to 15% of its normal area before disruption), the cell bursts. The method is effective

for isolated cells but is not so effective for tissues.

2. Homogenizers.

3. Sonication. This involves the generation of shear forces in a cell sample in the vicinity

of a titanium probe (0.5 mm in diameter and 10 cm long) that vibrates at ∼20,000 Hz.

The device contains a crystal of lead zirconate titanate that is piezoelectric; i.e., it

expands and contracts when an oscillatory electric field is applied to it from an

electronic oscillator. The ultrasonic pressure waves cause microcavitation in the

sample, and this disrupts the cell membranes, usually in a few seconds.

| cell structure |

Methods of studying the structure and function of cells ? Q&A - 1

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Question:Acidic dyes such as eosin and acid fuchsin have a net negative charge at the

pH of usual staining solutions. Therefore they bind to many cellular proteins that have a

net positive charge. Give some regions of a liver cell that might be acidophilic.?

Answer: The cytoplasm, mitochondrial matrix, and inside the smooth endoplasmic

reticulum; all regions have a high protein content.

| cell structure |

Methods of studying the structure and function of cells ? Q&A - 2

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Question:Basic dyes such as methylene blue or toluidine blue are positively charged at

the pH of most staining solutions used in histology. Thus the dyes bind to acidic

(negatively charged) substances in the cell. These acidic molecules are therefore

referred to as basophilic substances in cells. Give some examples of basophilic

substances?

Answer:Examples of basophilic components are DNA and RNA; the latter includes

messenger RNA and ribosomes.The youngest red blood cells in the blood circulation

contain a basophilic reticulum (network) in their cytoplasm; this is composed of

messenger and ribosomal RNA. The network is slowly dissolved over the first 24h of the

cell’s life in the circulation. This readily identifiable red cell type is called the reticulocyte.

| cell structure |

What does a typical animal cell look like?

Share|

There is no such thing as a typical animal cell, since cells vary in overall size, shape,

and contents of the

various subcellular organelles.

| cell structure |

What type of experiments can we carry out that might shed light on the origin of life?

Share|

A landmark experiment that was designed to provide some answers to this question

was conducted by Stanley Miller and Harold Urey, working at the University of Chicago

(see Fig. 1-1). Electrical discharges, which simulated lightning,were delivered in a glass

vessel that contained water and the gases methane (CH4), ammonia (NH3), and

hydrogen (H2),in the same relative proportions that were likely on prebiotic Earth. The

discharging went on for a week, and then the contents of the vessel were analyzed

chromatographically. The “soup” that was produced contained almost all the key

building blocks of life as we know it today: Miller observed that as much as 10–15% of

the carbon was in the form of organic compounds. Two percent of the carbon had

formed some of the amino acids that are used to make proteins. How the individual

molecules might have interacted to form a primitive cell is still a mystery, but at least the

building blocks

are known to arise under very plausible and readily reproduced physical and chemical

conditions

| cell structure |

Who first saw cells and sparked a revolution in biology by identifying these units as the basis of life?

Share|

It was Antonie van Leeuwenhoek (1632–1723), draper of Delft in Holland, and science

hobbyist who ground his own lenses and made simple microscopes that gave

magnifications of ~200 ×. On October 9, 1676, he sent a 17½-page letter

to the Royal Society of London, in which he described animalcules in various water

samples. These small organisms included what are today known as protozoans and

bacteria; thus Leeuwenhoek is credited with the first observation of bacteria. Later work

of his included the identification of spermatozoa and red blood cells from many species.

| cell structure |

What is the general nature of cells?

Share|

All animals, plants, and microorganisms are composed of cells. Cells range in volume

from a few attoliters among bacteria to milliliters for the giant nerve cells of squid; typical

cells in mammals have diameters of 10 to 100 µm and are thus often smaller than the

smallest visible particle. They are generally flexible structures with a delimiting

membrane that is in a dynamic, undulating state. Different animal and plant tissues

contain different types of cells that are distinguished not only by their different structures

but also by their different metabolic activities.

| cell structure |

| Botany | How do angiosperms differ from gymnosperms?

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First, the seeds of the angiosperms, a more recently evolved and highly successful

division of the tracheophytes, are enclosed within a protective chamber, the ovary. A

ripened ovary containing seeds is called a fruit. The fruit not only encloses the seeds

but may also aid in seed dispersal. The fruit is either carried or eaten by animals that

migrate to distant sites, carrying the seeds with them; the seeds are ultimately dropped

or eliminated from the animals’ digestive tracts.

The seed also forms a little differently in angiosperms. One sperm nucleus from the

pollen tube unites with an egg nucleus to produce the zygote. A second sperm nucleus

unites with two haploid nuclei in the gametophyte (embryo sac) to produce the triploid

endosperm, an important source of food within the seed for such seeds as corn.

In gymnosperms, pollination (transfer of pollen to female reproductive structure) can be

only wind-borne. In flowering plants, pollen may be transferred by wind or by animals.

Although insects have been stressed as prime agents for pollination, recent studies

suggest that mice and other small mammals may also play a role, particularly

in tropical plants.

A major internal modification of the angiosperms is the development of specialized

xylem cells, the vessels and fibers, in addition to tracheids. The vessels are particularly

significant because they are large-bore columnar cells that anastomose (join) end to

end. When their inner cellular contents degenerate, they collectively form long tubes

that greatly facilitate the passage of water in the plant. Fibers, on the other hand,

function solely to provide support. In conifers, the single

xylem elements, the tracheids, represent a more primitive condition

| Botany |

Criticize the following statement: Plants carry on photosynthesis; animals carry on respiration instead.

Share|

This is an incorrect view. Both plants and animals carry on respiration as a major source

of energy for vital functions. Only plants, however, are also capable of carrying out

photosynthesis. The components of photosynthesis are sequestered within the

chloroplast, whereas the major steps of respiration occur within the mitochondrion.

Thus, both processes may be occurring simultaneously in any plant cell, since the

compartmentalization of these functions precludes their interfering with each other.

Many of the sequences in the pathways of respiration are found as part of the

photosynthetic process; this suggests a close evolutionary association of the two

processes. The balance between respiration and photosynthesis will determine whether

there is a net uptake of O2 or CO2 from a particular plant region.

| Botany |

Describe some asexual processes occurring in animal reproduction. What is the chief disadvantage of this form of reproduction?

Share|

Parthenogenetic development of unfertilized eggs as a regular procedure in the

production of male ants and bees and Artificial stimulation of sea urchin eggs induces

cleavage. Although the egg is a sex cell, the development of unfertilized eggs is an

asexual process.Among sponges and hydra, budding is a common occurrence. This

involves an outgrowth of a portion of the parent’s body to produce a new individual.

Occasionally, the new growth will remain attached to the parent stock, but usually the

bud breaks away to produce an individual organism.

In the phylum, Platyhelminthes, a process called fragmentation occurs in which some of

these flatworms spontaneously separate into separate lengths. Each of the fragments

produces a new flatworm.

Related to fragmentation is regeneration, or the restoration of lost parts. Seemingly, this

is a mechanism for compensating for the accidental removal of organs or extended

structures. However, among the echinoderms

(starfish, brittle stars, etc.), the removal of an arm and part of the central disk leads to

the formation of a new organism from that arm, so that the process may be considered

both fragmentation and regeneration.

Asexual reproduction is a simple procedure for producing progeny, but it tends to

minimize the variation which is grist for the mill of evolution. It also tends to eliminate the

existence of parents, except in the instance of budding. In almost all animal organisms,

asexual reproduction is only a supplement to sexual reproduction.

| Botany |

Stripping a thin layer of bark completely around a tree trunk will kill the tree, but a deep gouge along one side will not. Why?

Share|

It must be remembered that the bark contains the phloem in its innermost region. The

circumcision of even a thin layer of bark completely disrupts the movement of organic

nutrients from the leaves and upper stem to the lower stem and roots. In a clear sense,

the roots and lower stem would be starved and their functions suspended. Survival

would be impossible.

On the other hand, a deep cut along one side of the trunk would disrupt completely both

nutrient flow in the phloem and fluid movement in the xylem, but only in the narrow band

of elements actually destroyed. The rest of the trunk would continue to provide a conduit

for necessary fluids and the sugars and other organic foodstuffs manufactured by the

leaves. Sometimes, it is possible for trees to survive even though their heartwood has

rotted or burned. Although this diminishes their strength, it does not reduce their ability

to transport nutrients, and so they survive.

| Botany |

| Biomolecules | What are the structural and chemical reasons why bile salts don’t form typical micelles?

Share|

Although bile salts possess a polar head group, the hydrocarbon tail usually contains

polar hydroxyl groups. Therefore the rigid ring system gives a tightly packed, almost

solid, nonpolar phase rather than a liquid one. However, like cholesterol, bile salts can

form mixed micelles with phospholipids.

| Biomolecules |

Can cholesterol form micelles and bilayers?

Share|

Cholesterol does not form micelles because it is not sufficiently amphiphilic (even

though it does have an OH group) and its flat, rigid, fused-ring structure gives a solid

rather than a liquid hydrocarbon phase at physiological temperatures. Such fluidity is

required for micelle formation. However, cholesterol can form mixed micelles with

amphiphilic lipids, and it enters monolayers as well where it constitutes ∼25% of the

mass of the lipid bilayer in the plasma membranes of mammalian cells.

| Biomolecules |

What is the chemical basis of this reactivity? β-D-Glucose

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Question

β-D-Glucose is the most prevalent monosaccharide in the bloodstream. It can react with

many differentcompounds. What is the chemical basis of this reactivity?

Answer

Glucose is an aldehyde and hence is a reducing compound. The aldehyde group is

reactive and can be reduced to form an alcohol, can be oxidized to form a carboxylic

acid, or can react with many other compounds to form a glucosyl adduct with them.

| Biomolecules |

What is the difference between a sugar and a carbohydrate?

Share|

Sugar is a term that is sometimes used incorrectly to refer to carbohydrates in general,

because many carbohydrates have a sweet taste. But not all carbohydrates are sugars,

e.g., starch. However, in common usage sugar usually refers specifically to sucrose, or

perhaps to a few other simple carbohydrates such as fructose and glucose.

| Biomolecules |

Is it strictly correct to call proline an amino acid?

Share|

No. The side chain of proline bends around and is covalently linked to the backbone

nitrogen atom replacing one of the hydrogen atoms. Thus it is actually an imino acid.

| Biomolecules |

Why is water such an important molecule in living systems?

Share|

The strength and specificity of interactions between biological molecules depend on the

medium in which they reside. The major biological solvent is water, although fat

deposits readily dissolve hydrophobic molecules such as some pesticides and various

drugs. Because of the large electronegativity of oxygen relative to hydrogen, the oxygen

atom attracts electrons from the two hydrogen atoms, making them more negative and

leaving the hydrogen atoms with a net positive charge. Thus, water molecules are

highly polarized, and they associate with one another through hydrogen bonds. The

angle between the two O—H bonds in water is not 180Degree; hence the molecule is

bent, and hydrogen bonds form in which each water molecule interacts with several

neighbors in a three-dimensional network. Without these interactions, water with a

molecular weight of 18 would be a gas at normal atmospheric temperatures and

pressures, like dinitrogen of molecular weight 28.

| Biomolecules |

What is inside a living cell?

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The inside of a cell is crowded with molecules, and these are in continuous vigorous

motion that is driven by thermal energy. In prokaryotic cells the cytoplasm is the only

compartment; in most eukaryotic cells it is still the largest single compartment. The

cytoplasm (also called the cytosol) is so crowded with small and large molecules that it

is significantly more viscous than a typical aqueous solution encountered in laboratory

experiments.

As molecules in random motion collide, they diffuse throughout the cell; large molecules

diffuse more slowly than

small ones. It is the diffusion and collisions between molecules that enable biochemical

reactions to occur.

| Biomolecules |

What is the nature of the interactions between biomolecules?

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Interactions between biomolecules depend on the forming and breaking of chemical

bonds.

The covalent bond is the strongest chemical bond. It links individual atoms within a

molecule and involves sharing of a pair of electrons between adjacent atoms. Its

formation requires considerable energy, and its breakage releases this energy. The

formation and breakage of covalent bonds are not readily reversible processes.

Noncovalent bonds are weaker and are often readily reversible. The four major ones

differ in their length,strength, specificity, and response to water. Although noncovalent

interactions are weaker than covalent bonds .

| Biomolecules |

What types of molecules are the foundations of life?

Share|

There are four major classes of biomolecules that are synthesized by living systems:

nucleic acids, proteins, lipids, and polysaccharides (carbohydrates). They are all

polymers of simple building blocks sugar, phosphate, and a nitrogenous base for the

nucleic acids; amino acids for proteins; glycerol and fatty acids for lipids; and simple

sugars (monosaccharides) for polysaccharides. These can be combined in some

specialized biomolecules such as carbohydrate and protein in glycoproteins; lipid and

protein in lipoproteins; and carbohydrate and lipid in glycolipids.

All biomolecules are remarkably similar throughout the evolutionary or phylogenetic

tree. Since living systems primarily exist within an aqueous environment, the unique

structures and properties of biomolecules are determined by their reactions within this

environment. The reactions between small molecules that take place in living systems

depend on higher-order interactions between the larger biomolecules that modify the

aqueous environment.

| Biomolecules |

“What is life?”

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There is no universal definition, but most scholars agree that life exhibits the following features: 1. Organization exists in all living systems since they are composed of one or more cells that are the basic units of life. 2. Metabolism decomposes organic matter (digestion and catabolism) and releases energy by converting nonliving material into cell constituents (synthesis). 3. Growth results from a higher rate of synthesis than catabolism. A growing organism increases in size in many of its components. 4. Adaptation is the accommodation of a living organism to its environment. It is fundamental to the process of evolution, and the range of responses of an individual to the environment is determined by its inherited traits. 5. Responses to stimuli take many forms including basic neuronal reflexes through to sophisticated actions that use all the senses. 6. Reproduction is the division of one cell to form two new cells. Clearly this occurs in normal somatic growth, but special significance is attached to the formation of new individuals by sexual or asexual means.

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Biology - Questions & Answers CSIR NET Paper II Life-Science