AP Biology Chapter 6 (Portion of 5)

Dr. Laurie Solis

Eukaryotic Cells

• A Eukaryotic cell is a three-dimensional structure composed of carbohydrates, lipids (fats), nucleic acids, and proteins.

AP Biology Chapter 6 (Portion of 5)

Dr. Laurie Solis

It all starts with a cell…

Cells are the basic unit of life in all living organisms

Life on earth…

• Life on earth can be traced back 3.7 billion years beginning in the form of a single celled organism

• Cells of all living organisms share similarities as part of our common evolutionary past.– Our focus is on eukaryotic

cells because they are found in multi-cellular organisms.

Eukaryotic Cells

• A Eukaryotic cell is a three-dimensional structure composed of carbohydrates, lipids (fats), nucleic acids, and proteins.

Eukaryotic Cells, contd.

Cytoplasm – gel like structure that protects the nucleus

DNA and RNA – genetic info that controls the cells functions

(deoxyribonucleic acid) and (ribonucleic acid)

Mitochondria- responsible for producing energy; contain their own distinct DNA – mitochondrial DNA; inherited only from the mother

Ribosomes – essential to protein synthesis

DNA

• DNA is the very basis of life!

– Watson and Crick discover DNA in 1953. (Cambridge University)

– Revolutionized biology, medicine and the understanding of evolutionary processes. James Watson (left) and Francis Crick in 1953

DNA: We share 50% of our DNA with bananas…

• The genetic code is universal• DNA is the genetic material in all

forms of life• The DNA of all organisms is

composed of the same molecules– For example, the same code CGA

specifies amino acid alanine – regardless of the species.

• DNA is like a universal language.• DNA shows us the connectivity

between all living things -- the biological relationship between all living things.

• What makes species unique is not differences in DNA material, but differences in how the DNA material is arranged.

Other DNA facts you don't need to know:- A parent and child share 99.5% of the same DNA.- We share 40-50% of our DNA with cabbages.- Humans share 98% of their DNA with chimpanzees.- Every human on earth shares 99% of their DNA with every other human.- Identical twins share the exact same DNA - meaning their DNA is 100% identical.- We share 60% of our DNA with a fruit fly.- Researchers at Cambridge University are convinced that the mud worms not only share DNA with humans but that they are also our closest invertabrae relatives.

DNA contd.

• The DNA molecule is made of up two chains of smaller molecules called nucleotides.– Forms a double helix shape– Nucleotides are composed

of sugar, phosphate, and one of four DNA bases.

• Bases are: adenine (A), guanine (G), thymine (T), and cytosine (C)

• One type of base can only bond with another type (i.e. A to T and G to C)

• This is essential to DNA’s ability to replicate itself.

Sugars and phosphates

Bases and bonds

DNA bases

• The four bases of DNA– A = Adenine– G = Guanine– T = Thymine– C = Cytosine– http://nobelprize.org/educational_games/m

edicine/dna_double_helix/

A T

AT

GC

CG

DNA Replication

• Cells have to multiply• Cell multiplication is made

possible by cell division• Cells multiply in a way that

each new cell receives a full set of genetic material–This is important because

a cell can’t function properly without the right amount of DNA

–For this to happen, DNA must first replicate

DNA Replication

• Before a cell divides, enzymes, break the bonds between bases of the DNA molecules

• The exposed bases attract unattached DNA nucleotides, present in the cell nucleus

• Since each base can only pair with only one another, the attraction between bases occurs in a complementary way.– That means the previously

joined parental nucleotide chains serve as models or templates for forming the new strands of nucleotides.

Characteristics of DNA

1. The DNA Code is universal – same basic messages apply to all life forms on the planet from bacteria to mammals

2. The DNA Code is triplet – each amino acid is specified by a sequence of three bases in the mRNA, which in turn is coded for by three bases in the DNA

3. The DNA Code is continuous – without pauses.

4. The DNA Code is redundant – it replicates itself

Protein Synthesis

• One of the most important activities of DNA is to direct the manufacture of proteins.– Collagen: structural

component of tissue (skin)– Hemogloben: carries oxygen

throughout the body– Enzymes: lactase, breaks

down lactose.– Hormones

• Insulin: allows the liver and muscle tissue to absorb glucose

Amino Acids• Proteins are made up of chains of

smaller molecules called amino acids.

• What makes proteins different from one another is the number and sequence of their amino acids.

• There are 20 amino acids, combined in different amounts and sequences to produce at least 90,000 different proteins.

• For a protein to function properly – amino acids must be arranged in their proper sequence

• Amino acids – small molecules that are the components of proteins

Protein Synthesis contd.• Regulatory Proteins – enter a cells

nucleus and attach directly to the DNA– Regulate DNA activity

• Protein Synthesis has to occur accurately - if it doesn’t, psychological and cellular activities can be disrupted or even prevented.

• Ribonucleic acid (RNA) – a single stranded molecule, similar in structure to DNA. Three forms of RNA are essential to protein synthesis. These are messenger RNA, transfer RNA, and ribosomal RNA.

The term synthesis (from the ancient Greek σύνθεσις σύν "with" and θέσις "placing") is used in many fields, usually to mean a process which combines together two or more pre-existing elements resulting in the formation of something new. The verb would be to synthesize meaning to make or form a synthesis. Synthesis may refer to:

messenger RNA The first step in protein synthesis is to copy the DNA

message into a form of ribonucleic acid called mRNA. messenger RNA - a form of RNA that is assembled on a

sequence of DNA bases. This carries the DNA to the ribosomes during protein synthesis.

This is the first step in protein synthesis is to copy the DNA message into a form of ribonucleic acid called mRNA.

This takes place outside the cell nucleus in the cytoplasm

RNA differs from DNA in these ways: It’s single stranded It contains a different type of sugar It contains the base uracil as a substitute for the DNA base

thymine.

transfer RNA

– transfer RNA (tRNA) – the type of RNA that binds to specific amino acids and transports them to the ribosome during protein synthesis.

Ribosomal DNA

• Ribosomes are composed of a form of RNA and protein. Essential to the manufacture of proteins.

Protein Synthesis contd

• Exons– Segments of genes

involved in protein synthesis• Ex means they are

expressed• Introns

– Segments of genes initially transcribed and then deleted; therefore they are not expressed – therefore are not involved in protein synthesis

• Exons and introns refer to specific nucleotide base sequences in the genetic code that are involved in producing proteins. Exons are the DNA bases that are transcribed into mRNA and eventually code for amino acids in the proteins. Introns are DNA bases, which are found between exons, but are not expressed. Genes which contain introns are known as interrupted genes.

What is a Gene?

• gene – a sequence of DNA bases that specifies the order (or sequence) of amino acids in an entire protein, a portion of a protein, or any functional product. – A gene may be made up of hundreds or

thousands of DNA bases organized into coding and non-coding segments.

• The gene codes for production of a polypeptide chain.– Polypeptide chain – A sequence of amino

acids that may act alone or in combination with others as a functional protein.

• A gene may be composed of only a few hundred bases, or thousands.

Regulatory Genes

• Some genes act solely to control the expression of other genes– These genes can switch other genes “on” or “off”.

Regulatory Genes

• An example of regulatory genes concerns DNA deactivation during embryonic development– While all somatic cells contain

the same information, only some of the cells will actually manifest

• For example, both the cells of the stomach lining and the cells in bones have DNA that codes for the production of digestive enzymes. Regulatory enzymes ensure that only the stomach lining will produce the digestive enzymes – i.e. to ensure each part of the body produces and functions properly

Regulatory Genes contd.

• Types of Regulatory Genes– Homeobox (Hox) genes: Extremely important gene. An

evolutionary ancient family of regulatory genes that directs the development of the overall body plan and the segmentation of body tissue.

• It interacts with other genes to determine the identity and characteristics of body segments and structures, but not their actual development.– Determines where limbs occur– Establishes the pattern and number of vertebrae– Hox genes are present in all insects and vertebrates and

don’t vary greatly from species to species.

Hox genes contd.

• Hox genes are important because they are conserved – meaning they don’t really change from species to species – they are the pretty much the same.– Hox genes evolved from genes

present in the earliest forms of life.– Hox genes are responsible for various

physical differences between closely related species, like humans and chimps.

Mutation

• If the sequence of bases is altered by a mutation – then the manufacture of proteins can’t happen, and the cell may not function properly or not at all.– Mutation – A change in DNA . Mutation refers to changes

in DNA bases (specifically called point mutations) as well as to changes chromosome number and/or structure.

Harmless changes like flower color….

Mutation contd.

• One example of a mutation is ‘sickle cell anemia’.– Sickle cell anemia: A severe inherited hemoglobin disorder in

which red blood cells collapse when deprived of oxygen. It results from inheriting two copies (from both parents) of the mutant allele. This allele is caused by a single base substitution in the DNA.• People become anemic through loss of oxygen and get

sick (impaired circulation from blocked capillaries, destruction of red blood cells, oxygen deprivation to the vital organs, can lead to death).

• However, people who only inherit the gene from one parent don’t get sickle cell anemia.

Sickle Cell Anemia-

• In fact, people with sickle cell have an immunity to malaria.

• Sickle cell anemia is an example of a point mutation; a chemical change in a single base of a DNA sequence.

Sickle Cell Anemia--

• According to the National Heart, Lung, and Blood Institute of the NIH, about 72,000 Americans are affected by sickle cell anemia (NHLBI 2003). In addition, about two million Americans are estimated to have sickle cell trait (they are carriers of the sickle cell allele) (NHLBI 2003). The sickle cell allele is much more common to certain ethnic groups; the allele is most frequent in people with Central or South American, Cuban, Indian, Saudi Arabian, Mediterranean, or African ancestries (NHLBI 2003). One in 600 African-Americans and one in 1000-1400 Hispanic Americans are born with sickle cell anemia (NHLBI 2003).

Chromosomes

• When cells divide to produce new cells, chromatin (which is loose diffused DNA – granular substance) becomes tightly coiled into chromosomes.

• Chromosomes: discrete structures composed of DNA and protein found only in the nuclei of cells. Chromosomes are visible under magnification only during certain phases of cell division.

Chromosomes

• Chromosomes are composed of DNA and proteins.• The two strands you see are a result of the DNA

replicating itself. One strand of the chromosome is an exact copy of another.

Chromosomes

• Humans have 46 chromosomes– Chimpanzees and Gorillas have 48– Humans don’t have less DNA – ours is just packaged differently.

• There are two types of chromosomes – Autosomes – carry genetic information that govern all physical

characteristics except sex determination– Sex chromosomes –

• X and Y• Y – in mammals the Y determines maleness• X – is more like an autosome, because it is the “default”

setting.• Offspring inherit one member of each chromosomal pair

from their father and mother.• These chromosomal pairs govern the same traits

Chromosomes

• Chromosomes contain almost all of the genetic information that determines inheritance.

• Different plant and animal species have different shapes and numbers of chromosomes.

• Having more chromosomes does not necessarily mean that an organism is structurally more complex.

• Having the same number of chromosomes does not mean that two animals are the same species.

Species # of Chromosomes

Cat 38

Pig 38

Cow 60

Goat 60

Dog 78

Chicken 78

Oxytricha (single celled organism)

46 million!

Cell Division

• Cell division is called mitosis– Simple cell division – the way cells reproduce. This

is what all cells do.• Meiosis – may lead to the development of new

individuals since it produced reproductive cells, or gametes. “Cell division in specialized cells in female ovaries and male testes. Meiosis involves two divisions and results in four daughter cells, each containing only half the original number of chromosomes.” If it weren’t cut in half, then it wouldn’t be possible to maintain the same number of chromosomes from one generation to the next.

Meiosis

• Meiosis is evolutionarily significant because– Increases genetic variation in populations– Ensures we are not ‘clones’– Each individual represents a unique combination of genes

due to the random assortment of chromosomes.

Meiosis

• If problems occur during meiosis and chromosomes don’t separate properly, the result will be 45 or 47 chromosomes.

• Most of the time this is lethal- except in one case.

• Down syndrome or Trisomy 21, is when there are 3 copies of chromosome 21.– Health affects: susceptibility to leukemia,

congenital heart defects, and mental impairment.– Most affected infants are born to women 35 and

older.

New Frontiers

• Advancements in the last two decades– Recombinant DNA technology

• Inject human genes that produce proteins in bacteria in order to produce insulin

• Human Genome Project: entire genetic makeup of an individual or species

– Began in 1990 and completed in 2003. – International effort aimed at sequencing and mapping the

entire human genome. – Human genome is comprised of 3 billion bases and

30,000 genes.• Important in biomedical research• How different genes function