During its life (cell cycle), a cell grows to a maximum size, then it undergoes DNA replication and mitosis.

Why do cells divide by mitosis?

To replace damaged or old cells (repair)

To grow (cells can’t get too large or they become inefficient in transporting material)

To reproduce a whole organisms asexually (without a mate)—clones! Hardly every happens in complex organisms like most plants and animals.

e.g., a plant grown from a cutting yeasts dividing in grape juice starfish regenerating after you tear it

in half

Somatic (body) cells divide by mitosis.Somatic cells are diploid in animals.

Mitosis starts with a diploid cell and ends with a diploid cell.

• Diploid=2n• 2 X n where n is the number of types of

chromosomes a species contains

• E.g., humans n=23• Body cells have 2 X 23 chromosomes before

and after mitosis

To make sex cells (gametes/sperm or eggs), body cells in the gonads (testes & ovaries)

divide by meiosis to produce gametes.

Meiosis begins with diploid body cells, 2n=46.Meiosis begins with haploid gametes, 1n=23.

Mendel’s law of segregation: It’s random for every chromosome (and every allele on it) whether a person’s maternal or paternal homologous chromosome is given.

Mendel’s law of independent assortment: The set of 23 chromosomes that each parent sorts into any particular gamete is random.

Human body cells are diploid with 2n = 46. Why? Body cells are produced by asexual mitotic division. Human gametes are haploid with 1n = 23. Why? Gametes are produced by sexual meiotic cell division.

Asexual reproduction or growth/repair of organisms utilizes mitosis (think My—

two—sis)

1 cell divides into two genetically identical daughter cells

Mitosis generates two genetically identical cells because the 2 copies of each chromosome are separated into two new daughter cells. The original cell is called the mother

cell.

Stages of mitosis from mother cells to genetically identical to 2 daughter cells.

http://highered.mcgraw-hill.com/sites/0073031216/student_view0/exercise13/mitosis_movie.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html

The only reason mitosis generates genetic differences is mistakes in copying DNA

• Mutations

• Mutations are sometimes bad, but sometimes they generate helpful or harmless differences alleles giving unique traits.

For sexual reproduction specialized cells called gametes (male sperm, female eggs) are required

These cells must have only 1 copy of each chromosome, not 2

Meiotic (meiosis, think my-o-sex) cell division generates 4 gametes with only 1 copy of each of the parent’s original pair of homologous chromosomes

How? Copy the DNA once, then divide twice.

Meiosis is used ONLY for sexual reproduction—it results in cells that are haploid (only 1 of each chromosome, 1n). Copy DNA once. Divide twice! For genetically reduced

(half as many chromosomes) gametes are produced.http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html

Human body cells are diploid with 2n = 46. Why? Body cells are produced by asexual mitotic division. Human gametes are haploid with 1n = 23. Why? Gametes are produced by sexual meiotic cell division.

Cell cycle regulation—mitosis and meiosis

http://outreach.mcb.harvard.edu/animations/checkpoints.swf

Requirements for passing cell cycle checkpoints in normally regulated cells

1 growth factor stimulation to activate exit from G0 or G12 Anchorage to a substrate (usually the extracellular matrix of another cell or with

a culture dish in vitro)—anchorage dependence3 At least some part of the cell membrane NOT in direct contact with another cell

(open space)—contact inhibition4 At the G1 checkpoint, minimal size & correct pairing of cyclins (made at specific

points in cell cycle) and cyclin dependent kinases, cdks (made throughout the cell cycle but only activated by a particular cell cycle phase regulated cyclin)

5 At the G2 checkpoint, DNA all replicated, not broken, well aligned via complementary base pairs; cyclin/cdk combination termed “mitosis promoting factor) is activated, and tumor suppressors like p53 or BRCA are NOT activated

6 At the anaphase (spindle) checkpoint, Spindle fibers connected to kinetichores/centromeres on both sides

When a checkpoint is not met, proteins like tumor suppressors stall the cell at the stage to allow for correction. If correction is not possible, apoptosis (cell suicide) is initiated.

Many proteins expressed in a cell cycle dependent manner monitor the checkpoints

http://lsresearch.thomsonreuters.com/static/maps/472_map.png

Cyclins made in a cell cycle stage dependent manner activate cyclin dependent kinases at key transitions

CarcinogensSubstances (like Components of cigarette smoke) or physical agents (like UV radiation) that are associated with high riskoncogene or tumor suppressor gene mutations.

http://www.mun.ca/biology/desmid/brian/BIOL2060/BIOL2060-19/1940.jpg

1st step in development of cancer: Immortalization—telomerase enzyme allows cells to continue dividing long after telomere degradation would

normally have signaled senescence (inability to divide again

http://www.quia.com/files/quia/users/lmcgee/mitosis/AP_Chapter_12/Density_Dependent_Inhibition_and_Cancer.jpg

As errors go unchecked and as cells become progressively more aneuploid (wrong chromosome #s),

mutations in more cell cycle regulatory genes occur.

Tumors are termed malignant when mutations allow them to migrate via blood and lymph vessels to new locations, then develop a tumor in the new location.

Cancer treatments either:remove the tumor by surgery OR induce apoptosis after radiation causes DNA damage ORtarget/inactivate proteins needed for cell cycle progression (chemotherapy) OR stimulate the patient’s immune system to recognize unique surface antigens of cancer cellscomplement mediated lysis (immunotherapy)

Advantages of using bioengineering—scans of human genome and its expression leads to detection of which genes are mutated & possible means of creating drugs that target these in a oncogene specific way

Oncogene—proteins with dominant mutations which allow cells to skip a checkpointProto-oncogene—normal version of an oncogene (side effects of chemotherapy are due to these also

being targeted by the drugs--> high cell death in rapidly dividing cell populations like stomach & intestinal lining or hair follicles

Tumor suppressor—regulators that are inactivated by recessive mutations, allowing cells that ought to undergo apoptosis to escape (inherited cancers affect tumor suppressor genes, making a mutation in a 2nd allele more likely)

Flow cytometric analysis of non-cancerous cells shows most cells in G0/G1

What is the length of G1, of S, and of G2/M in these cells? How many pg DNA in a diploid cell?

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter3/animation__random_orientation_of_chromosomes_during_meiosis.html

• http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter11/unique_features_of_meiosis.html

Stages of meiosishttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__stages_of_meiosis.htmlhttp://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter30/meiosis_with_crossing_over.html

Meiotic events are the basis for Mendel’s law of random segregation & independent assortment

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter3/animation__random_orientation_of_chromosomes_during_meiosis.html

http://www.sumanasinc.com/webcontent/animations/content/independentassortment.html

http://www.dnalc.org/view/16192-Animation-5-Genetic-inheritance-follows-rules-.html