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Cell cycle note - CELL CYCLE(Lodish Chapter 20 Introduction...

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CELL CYCLE (Lodish Chapter 20) Introduction A. Overview of cell cycle B. Events in each phase of the cell cycle C. The role of the cytoskeleton during the cell cycle D. The mechanism of cell division and the molecular checkpoints I. Major events in each stage of the cell cycle (Lodish Fig. 18-34). Cell replication: the cell cycle clock (Lodish Fig. 20-1, 2) A. G1phase: Cell growth; B. S phase: DNA synthesis & chromosome replication; C. G2 phase: DNA exist as chromatid; centrosome replication. Preparation for cell division. D. Mitosis: Cell division: mitosis and cytokinesis (M): 1. Prophase: Centrosome migration; chromosomes begin to condense, appearing as long threads. 2. Prometaphase: Spindle formation; nuclear envelope fragmentation; chromosome condensation completed and held together at their centromeres by spindle microtubules. 3. Metaphase: Chromosome alignment in the equatorial plane. 4. Anaphase: Chromosome separation. 5. Telophase and cytokinesis: Nuclear membranes re-formation; chromosomes decondensation; spindle disassembly; cell cleavage proceeds. 6. Cytokinesis: cytoplasmic division by contract ring. II. The machineries that drives cell division A. Centriole replication (Lodish Fig. 18-35) 1. Each centrosome contains a pair of centrioles 2. In late G1 phase, these two centrioles separate 3. In S phase, a new centriole starts to grow close to each old centriole 4. In G2 phase, the new centrioles further grow up and the new centrosomes mature 5. In prophase, the two centrosomes migrate to the two poles of the cell for formation of the mitotic spindle. B. Mitotic spindle formation (Lodish Fig. 18-35, 36) 1. Centrosomes 2. Asters and astral microtubules 3. The spindle body contains two kinds of microtubules: a. Kinetochore MT which connect to chromosomes, responsible for chromosome movement. b. Polar MTs, or overlap MTS, which do not contact chromosomes, most of them are released from the centrosomes after formation and held by motor proteins to the spindle pole body, overlap in the zone of interdigitation; responsible for symmetry an shape of the spindle. 1
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4. Motor proteins: plus-end-directed kinesin-related motor proteins enriched in the interdigitation region; plus-end-directed Dynein-related motor proteins enriched in the pole regions; 5. MT dynamics increases in mitosis due to loss of a stabilizing MAP (Lodish Fig. 18- 37). 6. MT in mitosis treadmill towards the spindle poles (Lodish Fig. 18-38). C. Chromosome movement (Lodish Fig. 18-39, 40, 41) 1. Kinetochore microtubules associated with the kinetochore of the replicated chromosome; 2. Kinetochore microtubules “search and capture” chromosomes (Lodish Fig. 18-40) 3. Motor proteins are involved in chromosome alignment in Metaphase (Lodish Fig. 18- 40) 4. Chromosome movement in Anaphase (Lodish Fig. 18-39, 40): a. kinetochore associated motor protein and depolymerization of kinetochore MT depolymerization pull chromosome to the poles b. Two models for force generation for chromosome movement: motor protein/ATP dependent, and motor protein/ATP independent c. Elongation of the overlap MTs push the two poles move apart.
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