1. The Cell Cycle Chapter 12 p. 218-228

2. Cell Division An important part of a cell’s life cycle is reproduction Cell Division: division of an existing cell into 2 genetically identical daughter cells 33 functions: 1) reproduction, 2) growth and development 3) tissue repair/renewal

3. Reproduction, Growth & Repair 1) Reproduction AAsexual: produces 2 identical cells (Mitosis) SSexual: combines DNA from 2 parents to form new offspring (Meiosis – Ch 13) 2) Growth DDevelopment of organism from 1 cell 3) Repair OOccurs throughout life i.e. RBC’s

4. Distribution of Chromosomes For most of cell cycle, DNA is packaged w/protein in chromatin (long, thin fiber) During Mitosis: 11) Identical copy of DNA is made 22) DNA condenses into chromosomes (46) Composed of 2 identical sister chromatids, connected by centromere

5. 33) Sister chromatids pull apart to opposite sides of cell 44) Cell splits, forming 2 new identical daughter cells (46 chromos. = diploid) During Meiosis, each parent supplies1/2 chromos. needed (23 chromos. = haploid)) Occurs in reproductive organs (ovaries/testes) Cells must divide twice to cut chromosome number in half

6. The Cell Cycle: an overview Most of cell’s life spent in Interphase (mitosis very brief)  Grow, produce proteins & organelles 3 Phases:  1) G 1 : grows to full size  2) S: replicates DNA  3) G 2 : prepares for mitosis

7. Phases of Mitosis: an overview 1) Prophase  DNA condenses  Nucleolus disappears  Spindle begins to form 2) Prometaphase  Nuclear envelope breaks apart  Spindles attach to kinetochore

8. 3) Metaphase CChromosomes line up on metaphase plate 4) Anaphase SSister chromatids pulled apart to opposite sides of cell 5) Telophase 22 new nuclear envelopes form CCytoplasm divides (cytokinesis), forming 2 new daughter cells Mitosis in action!!!

9. The Mitotic Spindle Consists of fibers of microtubules & proteins Assembled in centrosome at either end (pole) of cell Attach to kinetochore of each sister chromatid Align chromosomes along metaphase plate down center of cell

10. Cytokinesis “Division of cytoplasm” Cleavage: “pinching in” of plasma membrane along cleavage furrow PPlants develop cell plate → new cell walls

11. Mitosis in Plant Cells

12. Binary Fission Prokaryotic cell division DNA replicates, each copy moves to cell poles Plasma membrane grows inward & cell divides

13. Evolution of Mitosis

14. Regulation of the Cell Cycle Chapter 12 p. 228-235

15. Regulation of Cell Cycle: an overview Frequency of cell division depends on type of cell  i.e.: skin (fast), nerve (almost never) Cell Cycle Control System: directs events of cell cycle  Built-in molecular “clock” that triggers each phase  Regulated at internal/external checkpoints

16. Cell Cycle Checkpoints Occur at G 1, G 2, M phases SStop cycle until requirements for next phase are met IIf not, cell exits cycle & enters G 0 phase (non- dividing state) GG 1 Checkpoint: “restriction point” if clear, cell will usually complete cycle

17. Cell Cycle Clock Cycle is controlled by bonding of certain protein molecules in cell to each other 11) Cyclin-dependent kinases (Cdks) 22) Cyclin – conc. fluctuates Rises until M phase, then drops off Together, make MPF complex IInitiates mitosis by phosphorylating certain proteins TTurns off by destroying cyclin

18. Internal Signals Occur at anaphase WWill not proceed until all kinetochores are properly attached to spindles AAnaphase Promoting Complex (APC): becomes active, cyclin breaks down, chromatids separate

19. External Signals Most cells depend on external signals to control cell division 11) Growth Factors: proteins that stimulate other cells to divide i.e.: PDGF: stimulates platelet growth after injury (signal-transduction pthwy) 22) Density-Dependent Inhibition: cells stop dividing if become crowded 33) Anchorage Dependence: animal cells must be attached to substratum to divide

20. Cancer Cells Escape Cycle Controls Not affected by growth factors, density, or anchorage 11) Normal cell undergoes transformation → cancer cell 22) Cancerous cell reproduces to form tumor 33) If remains in place → benign  If spreads & impairs organs → malignant May enter bloodstream, have abnormal # chromosomes, affect metabolism Spread quickly (“metastasis”); may require radiation or chemotherapy