Understanding the Cell Cycle: Mitosis and Cell Division

1. The Cell CycleChapter 12

2. Mitosis • Cell division • Produce 2 daughter cells • Same genetic information

3. Mitosis • Asexual reproduction • Growth • Repair

4. Genome • Genetic information • Prokayotes • Nucleoid • Circular DNA • No nucleus

5. Genome • Eukaryotes • Chromosomes: • DNA • Associated proteins • Chromatin: • Complex of DNA & proteins • Makes up chromosomes • Humans 46 chromosomes • Dogs 78 chromosomes

7. Eukaryotes • Somatic cells: • Body cells • 46 chromosomes • Gametes: • Sex cells • Sperm & eggs • 23 chromosomes

8. Eukaryotes • Chromatid: • Duplicated chromosome • Centromere: • Attachment to another chromatid • Prior to cell division chromosomes replicates

9. 0.5 µm Chromosomes DNA molecules Fig. 12-4 Chromo- some arm Chromosome duplication (including DNA synthesis) Centromere Sister chromatids Separation of sister chromatids Centromere Sister chromatids

10. Fig. 12-5 INTERPHASE S (DNA synthesis) G1 Cytokinesis G2 Mitosis MITOTIC (M) PHASE

11. Cell cycle • Cell cycle: • Events that occur to produce two cells • 1. Interphase (G1, S, G2) • 2. Mitosis • 3. Cytokinesis

12. Interphase • Growth phase of the cell • G1, S, G2

13. Interphase • Where most of cycle is spent • Rate of division depends on job of cell. • Liver cells may divide rapidly • Mature muscle cells do not divide at all • Few cells will be in mitosis at a time • Most are in interphase

14. Interphase • G1 or Gap 1 phase • Cell is doing its job • Preparing for the S phase. • Chromosomes are single • Can last weeks to years or happen very quickly

15. Interphase • S phase DNA replication happens • 2 sister chromatids • G2 or Gap 2 phase cell prepares for division • Mitochondria & other organelles replicate • Microtubules begin to form • Chromosomes condense

16. Interphase

17. Mitosis • Nucleus & its contents divide • Distributed equally • Forming two daughter cells • Prophase, metaphase, anaphase and telophase

19. Prophase • Beginning of mitosis • Chromosomes continues to condense • Mitotic spindle forms • Begins to move chromosomes to center • Nuclear membrane disintegrates • Nucleolus disappears

20. Prophase

21. Metaphase • Chromosomes line up in center of cell • Centromeres become aligned along the cells center

22. Metaphase

23. Anaphase • Microtubules shorten • Separates the sister chromatids • Chromosomes move towards the poles

24. Anaphase

25. Telophase • Chromosomes are at the poles • Nuclear envelope reforms • Nucleolus reappears • Chromosomes uncoil or de-condense

26. Telophase

27. Cytokinesis • Cytoplasm separates • Animal cells: • cleavage furrow pinches the cells in two • Plant cells: • cell plate is formed between the cells • Grows until a new cell wall is formed

28. Cytokinesis

29. Fig. 12-9 Vesicles forming cell plate Wall of parent cell 1 µm 100 µm Cleavage furrow Cell plate New cell wall Daughter cells Contractile ring of microfilaments Daughter cells (a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM)

30. Binary fission • Prokaryotes produce 2 daughter cells by binary fission

31. Binary fission • 1. Replication of the DNA • Origin of replication: • Specific location on the DNA • 2. Two DNA molecules move to the ends of the cell • 3. Septation • Formation of a new cell membrane & a septum.

32. Binary fission • 4. Septum begins to grow inward • 5. Cell pinches into two cells.

33. Cell cycle control system • Check points • Control point with stop & go signals • G1, G2 and M phases

34. Fig. 12-14 G1 checkpoint Control system S G1 G2 M M checkpoint G2 checkpoint

35. Cell cycle control system • Special proteins • Protein kinases & cyclins • Cdks – cycle dependent kinases • MPF-cyclin-Cdk complex • “M-phase promoting factor” • Regulate if cell stops or proceeds in the cycle

36. Fig. 12-17b G1 S Cdk Cyclin accumulation M G2 Degraded cyclin G2 checkpoint Cdk Cyclin is degraded Cyclin MPF (b) Molecular mechanisms that help regulate the cell cycle

37. Figure 12.16a G2 M G1 G1 S M S M G1 G2 MPF activity Cyclinconcentration Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle

38. Cell cycle control system • Go-ahead signal at G1 • Divides • No signal • G0 phase • Does not divide

39. G1 checkpoint G0 Figure 12.17 G1 G1 Without go-ahead signal,cell enters G0. With go-ahead signal,cell continues cell cycle. (a) G1 checkpoint G1 S G2 M G1 G1 M G2 M G2 M checkpoint G2checkpoint Anaphase Prometaphase Metaphase With full chromosomeattachment, go-ahead signalis received. Without full chromosomeattachment, stop signal isreceived. (b) M checkpoint

40. Cell cycle control system • Receives signals • The environment • Other cells • Growth factors • Density-dependent inhibition • Anchorage dependence

41. Tumor • Abnormal growth of cells • Malfunction in control system • Abnormal cells grow uncontrollably • Benign: • Non-cancerous growth

42. Tumor • Malignant: • Cancerous growth • Metastasis: • Spread of cancer to distant locations

43. p53 • Protein • Works at a checkpoint at G1 • p53 determines if DNA is damaged • If so stimulates enzymes to fix it • Cell division continues • Unable to repair damage • Cell suicide occurs

44. p53 • Helps keep damaged cells from dividing • Cancer cells p53 is absent or damaged • p53 protein is found on the p53 gene • Considered a tumor-suppressor gene • Cigarette smoking causes mutations in this gene

45. Henrietta Lacks • 1951 developed cervical cancer • Before cancer treatment • Cells were removed • First cells to grow in vitro • Outside of the body • Cell line is now known as HeLa cell line • Helped in biomedical research