Cell Cycle Mitosis and Meiosis Biology is the

Cell Cycle, Mitosis, and Meiosis Biology is the only subject in which multiplication is the same thing as division… 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

Cell Cycle § Interphase: Divided into 3 phases: u l to a n sig ivide u d u G 1 = 1 st Gap § cell doing its “everyday job” § cell grows S = DNA Synthesis § copies DNA (chromosomes) G 2 = 2 nd Gap § prepares for division § cell grows (more) § Mitosis Phase u AP Biology cell division occurs G 0

Replicated Chromosome 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

There’s no turning back, now! Overview of Cell Cycle Control § Two irreversible points in cell cycle replication of genetic material u separation of sister chromatids u § Checkpoints regulate cycle u process is assessed & possibly halted centromere single-stranded AP Biology chromosomes sister chromatids double-stranded chromosomes

Checkpoint control system § 3 major checkpoints: Which checkpoint will start u G 1 prep for cell division? § can DNA synthesis begin? u G 2 § has DNA synthesis been completed correctly? § commitment to mitosis u M § are all chromosomes attached to spindle? § can sister chromatids separate correctly? AP Biology

Checkpoint Consequences: § If checkpoint is not met: u Exits cycle to G 0 phase (only if at G ) 1 § otherwise… Apoptosis – cell death AP Biology

How Do Cells Know When to Divide? § Chemical signals in cytosol § CYCLINS: Proteins that buildup in cytosol § CDK’s – “Cyclin Dependent KINASE” enzymes always present in cytosol u bind with cyclins to phosphorylate other proteins u AP Biology

CDK’s and Cyclins § More cyclins = more bonding with CDK § More CDK/cyclin complexes = cell division § more likely to happen or passing checkpoints Genes for CDK and cyclins are highly conserved through evolution. AP Biology

Checkpoint Failure: CANCER! § Uncontrolled cell division § Loss of checkpoint control § Oncogenes turned on (growth promoter genes) § Tumor suppressor genes off u p 53 major protein in checkpoint G 1 § Escapes apoptosis (no cell suicide) § Touch-sensor genes off u no density-dependent inhib § Blood vessel growth on AP Biology What are carcinogens?

What about Mitosis? § Evolved from Binary Fission of prokaryotes § Cells start and end diploid (2 N) Two sets of chromosomes; somatic cells u Starts with 1 cell and ends with 2 cells Stages: Prophase, Metaphase, Anaphase, Telophase with Cytokinesis u § Draw and label stages in notebook! AP Biology

Comparing Cytokinesis AP Biology

What about Meiosis? § Only when making sex cells (gametes) § Cells start 2 N, but finish haploid (N) § Start with 1 cell, end with 4 cells § Increases variability 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

Meiosis 1 and Meiosis 2 How many chromosomes in the cell? AP Biology At what point are the cells haploid? (Having 1/2 the number of chromosomes? )

Human male karyotype 46 chromosomes 23 pairs 2 sets 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

Crossing Over § A. K. A 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 § 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

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