Chapter 3 1

THE CELLULAR LEVEL OF ORGANIZATION

Chapter 3

Anatomy and Physiology Lecture

Chapter 3 2 THE CELLULAR LEVEL OF ORGANIZATIOM

Functions of the Cell

1. Basic unit of life 2. Protection and Support 3. Movement 4. Communication 5. Cell metabolism and energy release 6. Inheritance

How We See Cells

1. Light microscope 2. Electron microscope 3. Scanning electron microscope (SEM) 4. Transmission electron microscope (TEM)

Summary of Cell Parts 1. Plasma membrane. The outer, limiting membrane separating the

cell's internal parts from the extracellular materials and external environment.

2. Cytoplasm: Cytoplasm. The substance that surrounds organelles

and is located between the nucleus and the plasma membrane. All cellular contents located between plasma membrane and nucleus. Cytosol - the thick semifluid portion of the cytoplasm; which is intracellular fluid.

3. Cytoplasm: Organelles. Permanent structures with characteristic

morphology that are highly specialized for specific cellular activities. 4. Nucleus. The secretions and storage products of cells.

Chapter 3 3

PLASMA (CELL) MEMBRANE

Plasma Membrane, Cell Membrane, or Plasmalemma is the thin barrier that separates the internal components of a cell from the extracellular material and external environment. Fluid Mosaic Model of membrane structure describes the molecular arrangement of the plasma membrane and other membrane in living organisms. (Mosaic is a pattern of many small pieces fitted together). Fluid mosaic model describes membrane as a mosaic of proteins floating like icebergs in a sea of lipids. A. Membrane Chemistry and Anatomy By weight, plasma membrane of typical animal cells are about 50:50 mix of proteins and lipids. Proteins and Lipids are held together by noncovalent interactions. (Since proteins are larger and more massive than lipids, however, there are about 50 lipid molecules for each protein molecule). Membrane Lipids (a) Phospholipids (lipids that contain phosphorous) consist of about 75% of the lipids Phospholoids line up in two parrallel rows, forming a Phospholipid (lipid) bilayer. Phospopholids are amphipathic (that is, they have both polar and nonpolar regions.

Chapter 3 4 Polar part is the phosphate-containing “head”, which is hydrophilic (mixes with water). Nonpolar parts are the two fatty acid “tails”, which are hydrophobic (do not mix with water). (b) Glycolipids (Combination of Carbohydrate and Lipids) consist of 5% of membrane lipids. Glycolids, like phospholids are also amphipathic. Functions: (1) Are important for adhesion among cells and tissues. (2) May mediate cell-to-cell recognition and communication. (3) Contribute to regulation of cellular growth and development. (C) Cholesterol molecules ( a lipid) consists of 20% of membrane lipids. Cholesterol molecules are on both sides of the bilayer, located among the phospholipids in animal cells. The stiff steriod rings of cholesterol strengthen the membrane but decrease its flexibility. * Plant cell membranes lack cholesterol.

* (Bilayer is self-healing; if a needle is pushed through it and pulled out, the puncture site seals).

Membrane Proteins Fluid-mosaic model – Is the modern concept of the plasma membrane that suggests that the plasma membrane is neither rigid nor static in structure, but highly flexible and can change its shape and composition through time.

Chapter 3 5 Membrane Proteins are classified into two categories: Integral (intrinsic) and Peripheral (extrinsic) proteins: (a) Integral Proteins extend across the phospholipid bilayer among the fatty acid tails.

Are Glycoproteins (combination of sugar and protein)

Functions of Integral:

1. Some integral Protein (glycoprotein) form tiny channels (pores) through which certain subs flow into or out of the cell.

2. Others act as transporter (carriers) to move a substance from one side of the membrane to the other.

3. Serve as recognition sites called receptors. (b) Peripheral Proteins do not extend across the phospholipid bilayer.

Are loosely bound to the inner and outer surface of the membrane and are easily separated from it.

(Far less is known about Peripheral Protein than Integral Protein, and their functions are not yet completely understood.)

Generalized Functions of Membrane Proteins 1. Channel (Pore) 2. Transporter (carrier) 3. Receptor 4. Enzyme 5. Cytoskeleton anchor 6. Cell identity marker

Marker Molecules Marker Molecules are cell surfaces molecules that allow cells to identify one another or other molecules.

Chapter 3 6 Examples: (a) Glycoprotiens (proteins with attached carbohydrates) (b) Glycolipids (lipids with attached carbohydrates) Attachment Sites

Integrins are membrane-bound proteins that function as attachment sites. Channel Proteins

Channel proteins are one or more integral proteins arranged so that they form a tiny channel through the plasma membrane

Nongated ion channels are channel proteins that are always open and are responsible for the permeability of the plasma membrane to ions when the plasma membrane is at rest.

Ligands are small molecules that bind to proteins or glycoproteins, form the Ligand-gated ion channel.

Voltage-gated ion channel – When there is a charge across the plasma membrane.

Enzymes In The plasma Membrane

Enzymes: Some membrane proteins function as enzymes which can catalyze chemical reactions on either the inner or outer surface of the plasma membrane.

Carrier Proteins

Carrier proteins are integral membrane proteins that move ions or molecules from one side of the plasma membrane to the other.

Chapter 3 7 MOVEMENT THROUGH THE PLASMA MEMBRANE

Extracellular materials are separated from the Intracellular materials by the Plasma membrane. A Plasma membranes is Selectively Permeable, that is, it allows only certain substances to pass through it. In order for cells to survive, thing must move in and out of the cell. Certain substances, for example, must move into the cell to support life, whereas waste materials or harmful substances must be moved out. Four Ways By Which Substances Can Pass Through Plasma Membrane:

1. Directly through the phospholipid membrane 2. Membrane channel 3. Carrier molecules 4. Vesicles

Two processes involved in movement of material are:

1. Passive (physical) Processes - the substance move on their own down a concentration gradient; that is, from an area where their concentration is high to an area where their concentration is low.

*(Mechanisms that move substances across a membrane without using energy (released by splitting ATP).

The substance may also be forced across the plasma membrane by pressure from an area where the pressure is high to an area where it is low.

*Without an expenditure of energy.

2. Active (Physiological) Processes - the substance does not

move on its own. The substance moves against a concentration gradient, that is, from an area where its

Chapter 3 8 concentration is low to area where it is high.

*(Mechanism that move substances across a membrane by using energy released by splitting ATP).

*With an expenditure of energy.

Mechanism that move substances across a membrane by using energy (released by splitting ATP).

Diffusion

Diffusion is the movement of solutes from an area of higher concentration to an area of lower concentration in solution. Net Diffusion - the difference in diffusion between two regions having different concentration.

Equilibrium - point of even distribution. Concentration Gradient is the difference between high and low concentration. Viscosity is a measure of how easily a liquid flows; thick solutions, such as syrup. Are more viscous than water. Diffusion occurs more slowly in viscous solvents than in thin watery solvents. (Molecules moving from the high-concentration area to the low-concentration area are said to move down or with the concentration gradient.) Note: Diffusion of molecules is an important means by which substances move between the extracellular and intracellular fluids in the body. Example of diffusion in the body: The movement of oxygen from the blood

Chapter 3 9 into the cells and the movement of carbon dioxide from the cells back into the blood and within lungs. Osmosis Osmosis is the diffusion of water (solvent) across a selectively permeable membrane, such as plasma membrane. Osmotic pressure is the force required to prevent the movement of water by osmosis across a selectively permeable membrane. Tonicity: Osmosis may also be understood by considering the effects of different water concentration on red blood cells (cell shape).

a. Isotonic solution - a solution in which the total concentration of water molecules (solvent) and solute (solid) molecules are the same on both sides of the selectively permeable cell membrane.

*The normal shape of a red blood cell is maintained. ***(Under ordinary circumstances, a 0.9% NaCl (Salt) solution, called a normal saline solution, is isotonic for RBCs).

b. Hypotonic Solution - A solution that has a lower concentration of solutes. Higher water concentration.

-Water molecules enter the cells faster than they can leave, causing the red blood cells to swell and eventually burst.

-Rupture of red blood cells in this manner is called hemolysis.

(A process called lysis).

*(Distilled water is a strongly hypotonic solution.)

c. Hypertonic Solution - a solution that has a higher concentration of solutes and a lower concentration of water than the red blood cells. Lower water

Chapter 3 10

-Water molecules move out of the cells faster than they can enter, causing the red blood cells to shrink.

-Shrinkage of red blood cells in this manner is called crenation. *(2% NaCl solution is Hypertonic solution.)

Filtration Filtration is the movement of solvents (water) and dissolved substances

(solute) across a selectively permeable membrane by gravity or hydrostatic (water) pressure.

From area of high pressure to an area of lower pressure. Example in the body: Occurs in the kidney, where the blood pressure supplied by the heart forces water and small molecules like urea through thin cell membranes of tiny blood vessels and into the kidney tubules. *(Protein molecules remain in the blood since they are too large to be forced through the cell membrane of the blood vessels). (Molecules of many harmful substances and waste products are small enough to be filtered. They then can be eliminated in the urine). MEDIATED TRANSPORT MECHANISM Mediated transport mechanism involves carrier proteins within the plasma membrane that move large, water-soluble molecules or electrically charged molecules across the plasma membrane. Specificity means that each carrier protein binds to and transports only a single type of molecule. Competition is the result of similar molecules binding to the carrier protein.

Chapter 3 11 Saturation means that the rate of transport of molecules across the membrane is limited by the number of available carrier proteins. Three Kinds of Mediated Transport: 1. Facilitated Diffusion

Facilitated Diffusion - Is a carrier-mediated process that moves substances into or out of cells from a higher to a lower concentration.

Does not require metabolic energy to transport substance across the plasma membrane.

*Facilitated diffusion of glucose - is greatly accelerated by insulin, a hormone produced by the pancreas.

2. Active Transport Some substances cannot move (enter or leave) into the cell either because they are too big, have the wrong charge, or must move against the concentration gradient. Active Processes - Is a mediated transport process that requiresenergy provided by ATP. Active transport processes are important because they can move substances against their concentration gradients, that is, from lower concentration to higher concentration.

Example: The Sodium Pump Sodium Pump maintains a low concentration of sodium ion (Na+) in

the cytosol (intracellular fluid) by pumping then out against their concentration gradient. Also move Potassium ions (K+) into cells against their concentration gradient.

Chapter 3 12 3. Secondary Active Transport Secondary Active Transport – Involves the active transport of an ion such as sodium out of cell, establishing concentration gradient, with a higher concentration of the ions outside the cells. Secondary active transport indirectly uses energy obtained from splitting ATP, since the ion gradients themselves are established by primary active transport pumps. If Na+ can leak back in, some of the stored energy can be used to transport other substances against their concentration gradient.

Two examples of secondary active transport:

a. Symport (Cotransport) - when two substances (usually Na+ and another substance) move in the same direction across the plasma membrane.

Example: glucose, fructose, and amino acids enter cells living the gastrointestinal tract and the kidney tubules via symports that use Na+.

b. Antiport (countertransport) - when two substances (usually Na+ and another substance) move in opposite directions across the plasma membrane eg. Na+/Ca2+; Na+/H+, etc.

Endocytosis and Exocytosis How larger substances move across plasma membrane. Endocytosis - phagocytosis, pinocytosis, and receptor-mediated endocytosis are types of endocytosis. Are processes that bring bulk material through plasma membrane by the formation of a vesicle.

Chapter 3 13 Vesicle – Is a membrane-bounded sac found within the cytoplasm. 1. Phagocytosis or "cell eating" - projections of the plasma membrane and cytoplasm (psuedopods) surround large solid particles outside the cell and then engulf them. Phagocytic white blood cells and cells in other tissues engulf and destroy bacteria and other foreign substances; which constitutes a vital defense mechanism to protect us from disease. 2. Pinocytosis or "cell drinking" - the engulfed material is a tiny droplet of extracellular fluid rather than a solid. 3. Receptor-Mediated Endocytosis - similar to pinocytosis, but a highly selective process in which cells can take up specific molecules or particles.

Large molecules (eg. ligands) bond with receptors (specific proteins) and cross the plasma membrane. Example: The virus that causes AIDS enters cells by attaching to a glycoprotein receptor called CD4 that is present on certain types of white blood cells. Exocytosis - is a reverse process; it discharges substances from cells. Occurs in all cells but is especially important in nerve cells, which release their neurotransmitter substances by this process.

CYTOPLASM Cytosol Cytosol: Consist of a fluid portion, a cytoskeleton, and cytoplasmic inclusions.

Chapter 3 14 Cytoskeleton – Support the cells and holds the nucleus and organelles in place. Cytoskeleton Consists of Three Groups of Protein 1. Microtubles: Are large hollow tubules composed primarily of protein units called tubulin. 2. Actin filament or Microfilaments: Are small fibrils about 8 nm in diameter that form bundles, sheets, or networks on the cytoplasm of cells.

3. Intermediate filaments: Are protein fibers about 10 nm in diameter that provide mechanical strength to cells. Cytoplasmis Inclusions – Are aggregates of chemicals either produced by the cell or taken in by the cells. ORGANELLES Nucleus (Think of “Brain” or “Control Tower”) The largest structure in the cell; spherical or oval in shape. Contains the hereditary factors of the cell, called genes, which control cellular structure and direct many cellular activities. Contains genetic material which consists of deoxyribonucleic acid (DNA). Genetic material appears as a threadlike called Chromatin; when cell is not reproducing. Prior to cellular reproduction the chromatin shorten and coils into a rod-shaped bodies called chromosomes. Nucleoli are present inside the nucleus.

Chapter 3 15 Are aggregate of protein, DNA, and RNA that are not bounded by a membrane. Are sites of assembly of ribosomes which contain a type of RNA called ribosomal RNA - plays a key role in protien synthesis. Nucleoli disperse and disappear during cell division. Ribosomes (Think of the “Kitchen”) Consists of ribosomal Ribonucleic acid (rRNA) and ribosomal proteins. They occur free (singly or in cluster) Are the sites of protein synthesis. Endoplasmic Reticulum (ER) A system of membrane-enclosed channels of varying shapes called cisterns or cisternae. Is continuous with the nuclear envelope. Provides a surface area for chemical reactions and various products are transported from one portion of the cell to another via the ER. Divided into two types; based on its association with ribosomes: 1. Granular (rough) ER -Studded or attached with ribosomes. -Synthesize proteins

-Temporary storage area for newly synthesized molecules

Chapter 3 16 2. Agranular (smooth) ER -Do not contain ribosomes -Synthesize fatty acid, phospholipid, and steroid

-Can inactivate or detoxify a variety of channels, including alcohol, pestiudes, and carcinogens

Golgi Complex (Think of a “post office”)

Consists of four to six stacked, flattened membranous sacs (cisternae) referred to as cis, medial, and trans cisternae. Process, sort, and deliver proteins within the cell. Secretes proteins and lipids and forms lysosomes. Mitochondria (Think of “Powerhouse”)

Are called the "Powerhouses" of the cell, as they function in energy generating. Active cells, such as muscle, liver, and kidney tubule cells, have large number of mitochondria because of their high energy expenditure. Within mitochondria, energy is transferred from carbon compounds, such as glucose, to ATP. Mitochondria is composed of two membranes

a. The outer mitochondria membrane is smooth, but the inner membrane is arranged in a series of folds called cristae.

b. The central cavity of a mitochondrion enclosed by the inner membrane and cristae is called the matrix.

Chapter 3 17 Lysosomes (Think of “Suicide packets”)

Are formed from Golgi complexes. Function in Intracellular Digestion: Contain digestive enzymes; digest worn-out organelles by a process called autophagy (self-eat) Digests injured cell by a process called autolysis (self-destruct). Lysosomes are thereby called "suicide packets" Are found in large numbers in white blood cells, which carry on phagocytosis (cell eating). Functions in Extracellular Digestion

-(Prior to fertilization, the head of a sperm cell releases lysosomal enzymes capable of digesting a barrier around the egg so that the sperm cell can penetrate it.)

-Involved in bone removal (especially during the growth process)

Peroxisomes Similar in structure to lysosomes, but smaller. Are abundant in liver cells. Contain several enzymes (e.g. catalase) involved in the metabolism of hydrogen peroxide. Catalase

2H2O2 --------------------------- 2H2O + 2O2Hyrdogen Water Oxygen

Chapter 3 18 Peroxide

*Hydrogen peroxide is toxic to body cells. Centrosome and Centrioles A dense area of cytoplasm, generally spherical and located near the nucleus, is called centrosome (centrosphere). WIthin the centrosome is a pair of cylindrical structure called centrioles. Centrioles assume an important role in cell reproduction by helping to organize the mitotic spindle. Flagella and Cilia These cellular projections have the same basic structure and are used in movement. If projection are few (typically occurring singly or in pairs) and long, they are called flagella. If they are numerous and hair-like, they are called cilia. The flagellum on a sperm cell moves the entire cell. The cilia on cells of the respiratory tract move foreign matter trapped in mucus along the cell surfaces toward the throat for elimination. CELL INCLUSIONS Are large and diverse group of chemical substances produced by cells. Examples: 1. Melanin - a pigment stored in certain cells of the skin, hair, and eyes.

Chapter 3 19

-It protects the body by screening out harmful ultraviolet rays from the sun.

2. Glycogen - a polysaccharide that is stored in the liver, skeletal

muscle fibers (cells), and the vaginal mucosa.

-When the body requires quick energy, liver cells can break down the glycogen into glucose and release it.

3. Lipids - are stored in adipocytes (fat cells), may be decomposed for

producing energy. Extracellular materials -Are substances that lie outside the plasma membrane. -They provide support and a medium for the diffusion of nutrients and wastes. -Some, like hyaluronic acid and chondroitin sulfate, are amorphous (without shape). -Others, like collagenous, reticulae, and elastic fibers, are fibrous. OVERVIEW OF CELL METABOLISM Cell Metabolism – Is the sum of all the catabolic (decomposition) and anabolic (synthesis) reactions in the cell. Glycolysis – Converts the glucose to Pyruvic acid. Aerobic respiration – Occurs when oxygen is available. Anaerobic respiration – Occurs without oxygen and includes the conversion of Pyruvic acid to lactic acid.

Chapter 3 20 GENE ACTION Gene is a group of nucleotides on a Deoxyribonucleic Acid (DNA) molecule that serves as the master mold for manufacturing a specific protein. Cells are basically protein factories that constantly synthesize large numbers of diverse proteins. Proteins, in turn determine the physical and chemical characteristics of cells and therefore of organisms. Other proteins serve as hormone, antibodies, and contractile elements in muscle tissue. Others are enzymes. Deoxyribonucleic Acid (DNA) is a substance present in nuclei of cells consisting of phosphoric acid, a sugar, and nitrogenous bases. -It is a nucleic acid localized principally in the chromosomes. -It regulates protein synthesis and is the key molecule of the genes which give each cell its hereditary qualities and characteristics. PROTEIN SYNTHESIS Production of all the Proteins in the body is under the control of DNA. Building blocks of DNA are nucleotides containing: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). Triplet (every three nucleotides), code for an amino acid, and amino acids are the building block of proteins. Genes – Are all of the triplets required to code for the synthesis of a specific protein.

Chapter 3 21 Messenger RNA (mRNA) –Travels from the nucleus to ribosomes in the cytoplasm, where the information in the copy is used to construct a protein (i.e., translation). Transfer RNA (tRNA) – Carry the amino acid to the ribosome. Two principal steps in protein synthesis: (1) Transcription, and (2) Translation. Transcription is the process by which genetic information encoded in DNA is copied by a strand of RNA called messenger (mRNA). ---Occurs in the Nucleus. -By using specific portion of the cell's DNA as a template (base), the genetic information stored in the sequence of nitrogenous bases of DNA is rewritten so that same information appears in the nitrogenous bases of mRNA. Genetic information in DNA is copied to mRNA. When RNA synthesis is complete mRNA leaves the nucleus and enters the cytoplasm, where translation occurs. Translation is the process whereby information in the nucleotide sequence of mRNA specifies the amino acid sequence of a protein. ---Occurs in the Cytoplasm. *Just as DNA provides the template for mRNA to be made, so mRNA provides a template for protein synthesis. Transcription Translation DNA-----------------------------------RNA-----------------------------Protein

Chapter 3 22 CELL LIFE CYCLE Cell Life Cycle – Includes the changes a cell undergoes from the time it is formed until it divides to produce two new cells. Two Stages of Cell Life Cycle:

(1) An Interphase (2) A Cell Division Stage

IINTERPHASE (Metabolic Phase) Interphase is a phase when a cell is between divisions. - Consist of three distinct phases: G1, S, and G2 -The so called resting period between cell divisions -Represents 90% of the cell cycle -A period of great metabolic activity

a) Dispersal and Replication (synthesis or duplication) of DNA occurs, to ensure that each daughter cell receives the same genetic material as parent.

*It is during this stage that the replication (synthesis) of chromosomes occurs and the RNA and protein needed to produce structures required for doubling all cellular components are manufactured.

-Generation after generation, as a result of DNA replication and cell division, DNA is copied with great accuracy.

-Some mistakes in copying may be of no consequence, but some may be quite serious and may result in sickle-cell anemia and several forms of cancer.

Chapter 3 23 CELL DIVISION: Mitosis Cell division involves two major events:

(1) the division of the nucleus to form two new nuclei (2) the division of the cytoplasm to form two new cells.

Mitosis - is the distribution of the two sets of chromosomes into two separate and equal nuclei following the replication of the chromosome of the parent nucleus. Somatic Cells – Includes all human cells except the sex cells. Contains 46 chromosomes referred to as diploid. 46 chromosomes in somatic cells are organized into 23 pairs of chromosomes. Twenty-two pairs are called Autosomes. Each member of an autosomal pair of chromosome looks structurally alike, and together they are called a Homologous pair of chromosomes. Sex Chromosomes are the remaining two pairs.

1. X chromosome (female) – looks alike (XX) 2. Y chromosome (male) – does not look alike (XY)

1. Prophase: (The first phase of Mitosis)

-Formation of mitotic apparatus (Asters, Spindles, Centrioles, and Microtubules)

a. Chromatin shortens and coils into chromosomes.

Chapter 3 24

(Each prophase "Chromosome" is actually composed of a pair of structures called chromatids.)

(A chromatid is a complete chromosome consisting of a double-stranded DNA molecule, and each is attached to its partner by a small (spherical body called a centromere.)

b. Nucleoli and Nuclear envelope begin to break up and their components are resorbed into the endoplasmic reticulum.

c. Chromosomal microtubule and continuous microtubule, together called the mitotic spindle form between the separating centrioles.

d. The centrioles pairs move to opposite poles of the cell and radiate an array of microtubules called an aster (little star).

2. Metaphase:

Separation of sister chromatids.

a. The centromeres of the chromatid pair line up on the equatorial plane of the cell.

b. The centromeres of each chromatid pair form a chromosomal microtubule that attaches the centromere to a pole of the cell.

3. Anaphase:

Movement of the Chromosomes.

a. Centromeres divide and identical sets of chromosomes move to opposite poles of cell

b. considered the shortest phase.

Chapter 3 25 4. Telophase:

Re-formation of nuclei

a. Nuclear membrane reappears and encloses chromosomes b. Chromosomes resume chromatin form c. Nucleoli reappear d. Mitotic spindle disappears e. Centrioles duplicate f. End of mitosis

Cytokinesis: Partitioning the cytoplasm.

a. Cleavage furrow forms around equatorial plane of cell.

b. Separates cytoplasm into two separate and equal portions.

c. Two daughter cells are formed.

REPRODUCTIVE CELL DIVISION

Gametes -are specialized sex cells, the ovum produced in the female gonads (ovaries) and the sperm produced in the male gonads (testes).

Fertilization - the union and fusion of gametes.

Zygote - a single cell formed as a result of fertilization.

*Somatic cells have 46 chromosomes in their nuclei, or 23 pairs of chromosomes, and referred to as diploid cells (2n).

*Reproductive cells (gametes) have 23 chromosomes, and are referred to as haploid cells (n)

Chapter 3 26

Homologous Chromosomes or Homologous are two chromosomes that belong to a pair in a diploid cell.

**In human diploid cells, 22 of the 23 pairs of chromosome are morphologically similar and are called autosomes. Autosomes = 1 to 22 pairs of chromosome Sex chromosomes = 23rd pair of chromosome *The last pairs (23rd) of chromosomes is called Sex Chromosomes and designated as X and Y.

Male 6 XY: Sperm is either X or Y Female6 XX: Egg can only be X. MEIOSIS Reduction of chromosomes. Occurs only in the development of gametes, and it results in the production of cells that contain only 23 chromosomes. Spermatogenesis is the formation of haploid sperm cells in the testes of the male. Oogenesis is the formation of haploid ova (eggs) in the ovaries of the female. *Meiosis occurs in two successive nuclear divisions referred to as reduction division(Meiosis I) and equatorial division (Meiosis II).

Chapter 3 27 I. REDUCTION DIVISION (MEIOSIS I )

a. Interphase

-Replication of chromosomes (similar to that of Mitosis) (Reduction division begins, once chromosomal replication is complete).

Reduction Division Consists of Four phases:

b. Prophase I

1. Chromosomes shorten and thicken. 2. Nuclear membrane and nucleoli disappear. 3. Centrioles replicate and mitotic spindle appears.

*Unlike the Prophase of Mitosis, in Prophase I of Meiosis; - Chromosomes become arranged in homologous pairs. -The pairing is called Synpasis. -The four chromatids of each homologous pair are referred to as a Tetrad.

4. Crossing-over occurs-- portions of one chromatid may be exchange with portions of another.

(This process, among others, permits an exchange of genes among chromatids so that subsequent daughter cells produced are unlike each other genetically and unlike the parent cell that produce them.)

c. Metaphase I

1. Paired chromosomes line up along the equatorial plane of the cell, with one member of each pair on either side.

(Recall that there is no pairing of homologous chromosomes during the metaphase of mitosis.)

Chapter 3 28 d. Anaphase I

1. Separation of the members of each homologous pair, with one member of each pair moving to an opposite pole of the cell.

(During Anaphase I, unlike mitotic Anaphase, the centromeres do not split and the paired chromatids, held by a centromere, remain together.)

e. Telophase I and Cytokinesis are similar to those of mitosis. II. Equatorial Division (Meiosis II)

a. Interphase II

-The interphase between reduction division and equatorial division is either brief or lacking altogether.

-There is no replication of DNA.

b. Prophase II, Metaphase II, Anaphase II, and Telophase II are

similar to those that occur during mitosis.

*During equatorial division, the two haploid daughter cells undergo mitosis, and the net result is four haploid cells.

*All four haploid cells develop into sperm cells in the testes of the male.

*Only one of the haploid cells has the potential to develop into an ovum in the female. The other three become structures called polar bodies that do not function as gametes.

*Comparison between Mitosis and Meiosis.

Chapter 3 29

ABNORMAL CELL DIVISION: CANCER (CA) Tumor, Growth, or Neoplasm - the excess of tissue that develops when cells in some area of the body duplicate without control. Oncology - the study of tumor. Oncologist - a physician who specializes in tumor. Malignant tumor - a cancerous growth. Benign (tumor) growth - a noncancerous growth. Metastasis - the spread of cancer from its primary site. Carcinogens - are chemicals or environmental agents that can produce cancer. Oncogenous - are genes that can transform normal cells into cancerous cells.

CELLS AND AGING Aging is a normal process accompanied by a progressive alteration of the body's homeostatic adaptive response. Geriatrics - the specialized branch of medicine that deals with the medical problems and care of elderly persons. Clinical Application - Types of Cancer 1. Carcinomas - Malignant tumors that arise from epithelial cells. 2. Melanomas - Cancerous growths of melanocytes, skin cells that

Chapter 3 30 produce the pigment melanin.

3. Sarcoma - is a general term for any cancer arising from muscle cells

or connective tissue, e.g. Osteogenic Sarcomas - most frequent type of childhood cancer, destroy normal bone tissue (cosmetic tissue) and eventually spread to other areas of the body.

4. Leukemia - a cancer of blood-forming organs characterized by rapid growth and distorted development of leukocytes (white blood cells) and their precursors.

5. Lymphoma - a malignant disease of lymphatic tissue, for example,

lymph nodes.

-Hodgkin's disease, for example.