Chapter 12 - The Cell Cycle

1. Chapter 12 - The Cell Cycle

2. How did you develop from a single-celled zygote to a 300-trillion-celled organism? • How does the genetic information in a cell from your toe compare to the genetic information in a cell from your arm?

3. Cell Theory • All living matter is composed of one or more cells. • The cell is the structural and functional unit of life. • All cells come from cells. • So how does cell divide?

4. Roles of Cell Division • Reproduction • Growth • Repair • In all cases, cell division must distribute identical genetic material to two daughter cells.

5. Genome • Genome – the sum total of an organism’s genetic material • A typical human cell has about 2m of DNA (250,000 x a cell’s diameter)! • Usually packaged into chromosomes for manageability.

8. Chromosomes • Made of a DNA and protein complex called Chromatin. • During cell division, the chromatin becomes highly condensed into the chromosomes. • Why condense? – You have to separate a bowl of pasta into two plates. What’

9. Chromosomes - Structure • At cell division, each chromosome has been duplicated. • The duplicated chromosome consists of two sister chromatids.

11. Centromere • The point where two sister chromatids are connected.

12. Goal of cell division • To split the sister chromatids and give one to each new cell.

13. Draw out mitosis with 1 chromosome starting before DNA replication and then the resulting daughter cells.

14. Cell Cycle - parts 1. Interphase - (90% of cycle) - when the cell grows and duplicates the chromosomes. 2. Mitotic Phase (M) - when the chromosomes are split into separate cells.

16. Interphase

17. Interphase - parts • G1 (Gap 1) - Cell grows and carries out regular biochemical functions. • S – synthesis - When the DNA is replicated or synthesized. Chromosomes are replicated. • G2 – (Gap 2)- Cell completes preparations for division.

19. Mitotic Phase - parts 1. Mitosis - division of replicated chromosomes. 2. Cytokinesis - division of the cell’s cytoplasm.

20. Mitosis - Purpose • To divide the 2 copies of the DNA equally. • To separate the sister chromatids into separate cells.

21. Mitosis Steps • Prophase • Prometaphase • Metaphase • Anaphase • Telophase • You DO NOT need to know what happens in each stage. You do need to know the logic of the sequence of events • http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html

22. The Mitotic Spindle • Mitotic Spindle: network of microtubules and proteins; assembles during prophase • Centrosome (animal cell): region that organizes microtubules; (where they start growing) • Interphase: single centrosome replicates • Prophase and prometaphase: centrosomes move apart and microtubles begin growing out of them • Aster: radial array of short microtubules (centrosomes at each pole) • SPINDLE = centrosomes, spindle microtubules, and asters

23. What are microtubules? • Part of cytoskeleton • Hollow tubes of tubulin • Function: • Maintain cell shape • Cell motility • Cell division • Organelle Movement

24. Prophase

25. Prophase • Nucleoli disappear. • Chromatin condenses into the chromosomes. • Centrioles separate to opposite ends of the cell. • Mitotic spindle begins to form.

26. Prometaphase

27. Prometaphase • Nuclear envelope dissolves. • Spindle fibers join with the kinetochore of the centromeres.

28. Metaphase

29. Metaphase • Centrioles now at opposite ends of the cell. • Chromosomes line up on the metaphase plate. • Spindle apparatus fully developed.

30. Anaphase

31. Anaphase • Centromeres break and the duplicated chromosomes are pulled away from each other toward opposite ends of the cell. • Cell elongates; poles move slightly further apart.

32. Kinetochores • Specialized regions of the centromeres where spindle microtubules attach.

33. Kinetochores • Structure on the chromosome • Appear to “ratchet” the chromosome down the spindle fiber microtubule with a motor protein. • Microtubules dissolve behind the kinetochore.

35. Telophase

36. Telophase • Chromosomes uncoil back to chromatin. • Nuclear envelope reforms. • Nucleoli reappear. • Spindle fibers disappear. • Cytokinesis usually starts.

37. Cytokinesis

38. Cytokinesis - Animal • Cleavage furrow forms. • Microfilaments contracts and divides the cytoplasm into two parts.

39. Cytokinesis - Plants • Cell plate develops from Golgi vesicles. • New cell wall developed around the cell plate.

40. Cell Plate

41. Cell Division

42. Animal Cell - Mitosis

43. Plant Cell - Mitosis

45. Regulation of Cell Division • Must be controlled. • Rate of cell division depends on the cell type. • Ex - skin: frequently • liver - as needed • brain - rarely or never

46. Checkpoints • A critical control point in the cell cycle. • Several are known. • Cells must receive a “go-ahead” signal before proceeding to the next phase.

47. G1 Checkpoint • Also called the “restriction point” in mammalian cells. • Places cells in a non-dividing phase called the Go phase. • Most important checkpoint according to some.

48. GO

49. Go Phase • Non-dividing state. • Most cells are in this state. • Some cells can be reactivated back into M phase from the Go phase.

50. Protein Kinase Checkpoint - G2 • Uses protein kinases to signal “go-ahead” for the G2 phase. • Activated by a protein complex whose concentration changes over the cell cycle.