Unit 4 Cell Cycle Mitosis and Meiosis Biology

Unit 4: Cell Cycle, Mitosis, and Meiosis Biology is the only subject in which multiplication is the same thing as division… Chapters: 12 and 13 AP Biology 2007 -2008

The Cell cycle § “Life cycle” of a cell is formed from a mitotic division cell grows & matures to divide again G 1, S, G 2, M epithelial cells, blood cells, stem cells AP Biology cell grows & matures to never divide again liver cells G 1 G 0 brain / nerve cells muscle cells

The Cell Cycle § Interphase u l to a n de g i s ivi d u G 1 = 1 st Gap § cell doing its “everyday job” § cell grows S = DNA Synthesis § copies DNA (chromosomes) u G 2 = 2 nd Gap § prepares for division § cell grows more § Mitosis u u AP Biology PMAT Cytokinesis G 0 (Out of cycle Never divides)

The S-Phase: Replicating Chromosomes 2 sister chromatids u narrow at centromeres u contain identical copies of original DNA u Why copy the DNA? AP Biology

How is this process regulated/controlled? What if it gets out of control? AP Biology

The Checkpoints - process can be stopped § G 1 - Has enough growth occurred? can DNA synthesis begin? § G 2 - has DNA synthesis been completed correctly? committed to mitosis § M - are all chromosomes attached to spindle? can sister chromatids separate correctly? AP Biology

Two Irreversible Points: § Replication of genetic material There’s no turning back, now! § Separation of sister chromatids centromere single-stranded AP Biology chromosomes double-stranded chromosomes

If checkpoint is not met…. 1. Repair DNA if possible 2. Exit to G 0 phase (only at G ) 1 3. Or… Apoptosis – cell death AP Biology

Chemicals that Regulate Cell Division § Found in cytosol § CYCLINS: Proteins that buildup in cytosol § CDK’s: “Cyclin Dependent Kinase” enzymes CDK binds with cyclins to phosphorylate other proteins that carry out mitosis AP Biology

MPF = Cyclin + CDK § MPF needed to promote cell division § Cyclins broken down after use § Genes for CDK and cyclins are highly conserved through evolution. (useful) AP Biology

What are carcinogens? Things that cause cancer CANCER § Uncontrolled cell division § Loss of checkpoint controls § Oncogenes turned on (growth promoter genes) § Tumor suppressor genes off § Escapes apoptosis § Blood vessel growth on AP Biology

M-Phase (Cell Division) § Why would cell division occur? § Evolved from Binary Fission of prokaryotes § Mitosis – division of the nucleus u Cells start and end diploid (2 N) § Two sets of chromosomes; somatic cells u u Stages: PMAT with Cytokinesis 2 identical cells at the end of process Put a diagram in notebook! AP Biology Must know basic happenings for each stage!

Comparing Cytokinesis How are the processes different? AP Biology

What about Meiosis? § Only when making sex cells (gametes) § Cells start diploid 2 N, but end haploid N § Start 1 cell…end with 4 cells § Increases genetic variation by: genetic recombination (sperm/egg) u crossing over by chromosomes u § Goes through 2 cycles: u Meiosis 1 and Meiosis 2 § P 1 M 1 A 1 T 1 and P 2 M 2 A 2 T 2 AP Biology

Homologous chromosomes § Paired chromosomes u both chromosomes of a pair carry “matching” genes § homologous = same information diploid 2 n 2 n = 4 AP Biology single stranded homologous chromosomes TETRAD : 4 chromatids double stranded homologous chromosomes

Human male karyotype 46 chromosomes 23 pairs 2 sets AP Biology

Meiosis simplified… How many chromosomes in the cell? Put a complete diagram in notebook! AP Biology At what point are the cells haploid? (Having 1/2 the number of chromosomes? )

Crossing Over or Synapsis § During Prophase 1 homologous pairs (tetrads) swap genetic material Increases genetic variations u § AP Biology

2 n = 4 single stranded Meiosis 1 § 1 st division crossing over occurs u separation of homologous pairs u 2 N to N (diploid to haploid) u prophase 1 2 n = 4 double stranded metaphase 1 2 n = 4 double stranded reduction telophase 1 AP Biology 1 n = 2 double stranded

Meiosis 2 (like mitosis, no interphase before start) § separates sister § § chromatids stays haploid 4 cells at end 1 n = 2 double stranded 1 n = 2 single stranded AP Biology 1 n = 2 double stranded prophase 2 metaphase 2 4 telophase 2

Mitosis vs. Meiosis § Mitosis u u u AP Biology 1 division daughter cells genetically identical to parent cell produces 2 cells 2 N produces cells for growth & repair no crossing over § Meiosis u 2 divisions daughter cells genetically different from parent produces 4 cells 2 N 1 N produces gametes u crossing over u u

Putting it all together… meiosis fertilization mitosis + development gametes 46 meiosis 46 23 egg 23 23 23 zygote fertilization AP Biology sperm 46 46 46 mitosis development