1. Cell cycle and cell division
Charpter 9
Cell cycle and cell division
2nd Edition

2. Cell cycle and cell division
Overview of the cell cycle
Regulation of the cell cycle
Cell division

3. duplicated chromosomes
I. Overview of the cell cycle
cell growth
DNA replication
distribution of the
duplicated chromosomes
cell division

4. Overview of the cell cycle
The cell cycle can be divided into two major phases based on cellular activities, interphase and M phase.

5. Overview of the cell cycle

6. M phase includes mitosis and cytokinesis.
Overview of the cell cycle
M phase includes mitosis and cytokinesis.
Interphase is the interval between divisions divided into G1, S and G2 phases.

7. so the cell cycle includes four phases: G1, S, G2 and M phases.
Overview of the cell cycle
so the cell cycle includes four phases: G1, S, G2 and M phases.

8. Overview of the cell cycle
Analysis of a large variety of cells has revealed great variability in the lengths of their cell cycle.
The four stages of cell cycle, G1 is the most variable. While the total time of S, G2 and M phases is relatively fixed.

9. Regulation of The cell cycle

10. Regulation of The cell cycle
It is the cell-cycle control system that ensures correct progression through the cell cycle by regulating the cell-cycle machinery.
The progression of cells through the division cycle is regulated by extracellular signals from the environment and internal signals.

11. II. Regulation of The cell cycle
Cell cycle control
Cell Cycle Checkpoints
Cyclins
Progression regulatory of cell cycle

12. Cell cycle control
A major cell cycle regulatory point in many types of cells occurs late in G1 and controls progression from G1 to S.
In addition to serving as a decision point for monitoring extracellular signals, START is the point at which cell growth is coordinated with DNA replication and cell division.

13. Cell cycle control

14. Cell cycle control
The proliferation of most animal cells is similarly regulated in the G1 phase of the cell cycle. In particular, a decision point in late G1, called the restriction point in animal cells.

15. Cell cycle control
The proliferation of these cells is triggered by platelet-derived growth factor, which is released from blood platelets during clotting and signals the proliferation of fibroblasts in the vicinity of the injured tissue.

16. Cell Cycle Checkpoints
In most cells, the coordination between different phases of the cell cycle is dependent on a system of checkpoints and feedback controls that prevent entry into the next phase of the cell cycle until the events of the preceding phase have been completed.

17. Cell Cycle Checkpoints
At least, there are three major checkpoints exist within the cell cycle,
G1/S checkpoint ,
G2/M checkpoint
and M checkpoint .

18. Cell Cycle Checkpoints
The G1/S checkpoint monitors the cell size achieved following the previous mitosis, and whether the DNA has been damaged.

19. Role of p53 in G1 arrest induced by DNA damage
Cell Cycle Checkpoints
Role of p53 in G1 arrest induced by DNA damage

20. The second checkpoint: G2/M checkpoint
Cell Cycle Checkpoints
The second checkpoint: G2/M checkpoint
Check for:
Whether DNA replication is completed?
Whether centrosome has finished duplication?

21. Cell Cycle Checkpoints
The final checkpoint, M checkpoint, occurs during mitosis. It monitors the alignment of chromosomes on the mitotic spindle, thus ensuring that a complete set of chromosomes is distributed accurately to the daughter cells.

22. Cyclins
A series of experiments on the oocytes and early embryos of frogs revealed the existence of factors trigger DNA replication and promote a cell into mitosis or meiosis, and showed that entry of a cell into M phase is initiated by a protein kinase called MPF (maturation promoting factor or M phase-promoting factor ).

23. Cyclins
MPF is a dimeric kinase, containing a catalytic subunit and a regulatory subunit.
Regulatory subunit triggers the onset of mitosis, while the catalytic subunit transfers phosphate groups from ATP to specific serine(Ser) and threonine (Thr)residues of specific protein substrates.

24. The structural basis of the cyclin-dependent protein kinases
Cyclins
The structural basis of the cyclin-dependent protein kinases

25. Cyclins
The regulatory subunit’s concentration rises and falls in a predictable pattern as the cell cycle progresses, so called “cyclin”.

26. Cyclins
The cyclin that helps drive cells into M phase is called M-cyclin, cyclin A, cyclin B etc. Whereas, the cyclin that becomes active toward the end of G1 phase and is responsible for driving the cell into S phase is called G1-cyclin, for example, cyclin C and cyclin D.

27. Cyclin-Dependent Kinase and its Inhibitors
Cyclins
Cyclin-Dependent Kinase and its Inhibitors

28. Cyclins

29. Progression regulatory of cell cycle
Cyclins
Progression regulatory of cell cycle
A model for cell cycle regulation in fission yeast

30. Cdk phosphorylation state
Cyclins
Cdk phosphorylation state
Progression through the fission yeast cell cycle requires the phosphorylation and dephosphorylation of critical cdc2 residues

31. Control of proteolysis by SCF and APC
Cyclins
Control of proteolysis by SCF and APC

32. III. Cell division
Mitosis
Meiosis

33. Mitosis
Mitosis is a process of nuclear division in which replicated DNA molecules of each chromosome are faithfully partitioned into two nuclei.
Mitosis is conventionally divided into six stages, prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis.

34. Mitosis
prophase
prometaphase
metaphase
anaphase
telophase

35. Prophase 1.The chromosomal material condenses to form chromosomes.
Mitosis
Prophase
1.The chromosomal material condenses to form chromosomes.
2.Cytoskeleton is disassembled and mitotic spindle is assembled.
3.Golgi complex and ER fragment.
4.Nuclear envelope disperses.

36. chromosome condensation
Mitosis
chromosome condensation

37. Centromeres and kinetochores
Mitosis
Centromeres and kinetochores

38. Mitosis

39. Formation of the Mitotic Spindle
Mitosis
Formation of the Mitotic Spindle

40. The Dissolution of Nuclear Envelope and
Mitosis
The Dissolution of Nuclear Envelope and
the Partitioning of Cytoplasmic Organelles
The nuclear membranes are progressively fragmented, initially into flattened, saclike vesicles that surround the condensing chromatin, and eventually into a population of small spherical vesicles that disperse throughout the mitotic cell.

41. Mitosis
Prometaphase
The disassembly of the nuclear envelope, which breaks up into small membrane vesicles and dispersed into cytoplasm, marks the start of the second phase of mitosis, prometaphase.

42. 1, mitotic spindle assembly is completed
Mitosis
1, mitotic spindle assembly is completed
2, the chromosomes are moved into the center of the cell

43. Mitosis
Microtubule behavior during formation of the metaphase plate

44. Mitosis
Metaphase
Once all of the chromosomes has become aligned at the spindle equator, halfway between the two spindle poles, thereby forming the metaphase plate (equatorial plate) .

45. Mitosis
equatorial plate

46. three types microtubules of the metaphase spindle
Mitosis
three types microtubules of the metaphase spindle

47. Mitosis

48. Anaphase Centromeres split, and sister chromatids separate to form
Mitosis
Anaphase
Centromeres split, and sister chromatids separate to form
two daughter chromosomes.
2. The separated chromosomes move to opposite spindle poles.

49. Mitosis
Anaphase can be divided into two stages, anaphase A and anaphase B, and they occur more or less simultaneously.
In anaphase A, the kinetochore microtubules are shortened by depolymerization, and the attached chromosomes move poleward.
In anaphase B, the polar microtubules are gradually elongated, and the two spindle poles move farther apart.

50. Mitosis
Anaphase A
Anaphase B

51. Microtubules and motors in the spindle
Mitosis
Microtubules and motors in the spindle
In anaphase A, the (1) motors (dyneins) move to the minus ends of kinetochore microtubules and help the sister chromatids separate apart.
In anaphase B, (2) motors (kinesins) walk to the plus ends of interpolar microtubules and push the ploes to be far away each other. The (3) motors (dyneins) which is on the astral MT will fix two centrosomes at the poles of the cells.

52. Mitosis
Telophase
1.The two sets of daughter chromosomes cluster at opposite spindle poles and decondense.
2.Nuclear envelope reassembles around each sets of chromosomes cluster.
3.Golgi complex and ER reforms.

53. Mitosis
Cytokinesis
The cytoplasm is divided at equator plate to create two daughters, each with one nucleus.

54. Cytokinesis in animal cells
Mitosis
Cytokinesis in animal cells
the cleavage furrow

55. Mitosis
the contractile ring

56. Cytokinesis in plant cell
Mitosis
Cytokinesis in plant cell
Cytokinesis in a plant cell is guided by phragmoplast

57. Meiosis
Meiosis
Meiosis is a special kind of cell division, which only occurs at some stage of the sexual cell reproduction.
Meiosis involves a single round of DNA replication that duplicates the chromosomes, followed by two successive cell divisions, called meiosisⅠand meiosisⅡ.

58. Meiosis
MeiosisⅠ
It can be factitiously divided into five stages, prophaseⅠ, prometaphaseⅠ, metaphaseⅠ, anaphaseⅠand telophaseⅠ.
ProphaseⅠincludes leptotene, zygotene, pachytene, diplotene and diakinesis five stages.

59. Meiosis
ProphaseⅠ

60. leptotene The chromosomes condense and become
Meiosis
leptotene
The chromosomes condense and become
gradually visible in the light microscope, and
revealed to be composed of paired chromatids.
Near the end of leptotene, there is a dramatic
reorganization so that the telomeres become
localized at the inner surface of the nuclear
envelope at one side of the nucleus.

61. Meiosis
zygotene

62. Meiosis
synaptonemal complex
Electron micrographs indicate that chromosome synapsis is accompanied by the formation of a complex structure called the synaptonemal complex (SC). The SC is a ladderlike structure composed of three parallel bars with many transverse filaments connecting the central element with the two lateral elements.

63. Meiosis

64. Meiosis
pachytene
The end of synapsis marks the end of zygotene and the beginning of pachytene. During this period, the homologues are held closely together along their length by the SC . Recombination nodules form in this period.

65. Meiosis

66. Meiosis
diplotene
Diplotene is recognized by the dissolution of the SC and the tendency of the homologous chromosomes of the bivalents to pull away somewhat from each other.

67. Meiosis
diakinesis
During diakinesis the meiotic spindle is assembled, and the chromosomes are prepared for separation. Diakinesis ends with the disappearance of the nucleolus, the breakdown of the nuclear envelope, the terminalization of the crossover, and the movement of the tetrads to the metaphase plate.

68. Meiosis
Separation of homologous chromosomes during meiosis I and separation of chromotids during meiosis II.

69. Meiosis ---sexual cell reproduction

71. Summary Overview of the cell cycle Regulation of the cell cycle
Cell division