Biol110-10-Lecture 16-Mitosis - The mechanics of cell...

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DNA has been faithfully duplicated… The centriole has duplicated… Cell mass and size have reached critical size… All G2 checkpoints say go ahead… The mechanics of cell division nuclear division: mitosis cytoplasmic division: cytokinesis M-CDK becomes active and triggers M phase via a phosphorylation cascade. Induces chromosome condensation, nuclear envelope breakdown and increases microtubule dynamics. Actin cytoskeleton rearrangement and Golgi fragmentation. Mitosis and cytokinesis are accomplished using two cytoskeletal machines: The mitotic spindle and the contractile ring Segregation of chromosomes Two cell separation Spindle remnant is needed for the contractile ring
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The order of events Overview of the stages of mitosis : Chromosome condensation Centrioles on spindle assembly outside of nuclei Nuclear envelope microtubules engage chromosomes kinetochore microtubules engage chromosomes A. Chromatids separate synchronously B. Spindle poles move apart Chromosome decondensatio envelope reformation a b c d e f g h DNA duplication Centrosome duplication Key regulators for entry and exit from M phase: 1) Increase M-CDK activity at G2/M triggers early steps up to metaphase 2) The APC-triggered degradation of securin and cyclin promotes anaphase and telophase
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Interphase - Replication of DNA ORCs phosphate is removed after mitosis Cohesin ‘locks’ sister chromatids together after replication
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Interphase - Duplication of centrosomes Mammalian S phase duplicated centrosome Pure centrioles mother daughter Centrosome: centriole pair plus matrix Maintains cytoplasmic array of microtubules Has gamma tubulin, motors Daughter grows off mother at 90° They separate, but remain associated Dissociation in M phase -Daughter nucleates new microtubules DNA duplication Centrosome duplication
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As the levels of M-cyclin rise, it associates with CDK The resulting M-CDK is then activated and inhibited by CAK and Wee kinases, respectively At the end of G2, Cdc25 activates M-CDK by removal of inhibitory phosphate on CDK. What about Cdc25? Active M-CDK induces (via phosphorylation of various targets) mitotic spindle assembly, chromosome attachment to spindle, nuclear envelope breakdown, actin depolymerization, and ER and Golgi membrane re -organization M-CDK drives entry into mitosis M-CDK activates the activator M-CDK inhibits the inhibitor
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cohesins Condensins 50-fold compaction; M-CDK activates the coiling function of condensin Crosslinking molecules Prophase- Chromosome condensation via condensins condensins Chromosome condensation Chromosome condensation is an ATP-dependent process that changes the ‘coiling’ of DNA Condensin
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This note was uploaded on 01/17/2011 for the course BIOL 110 taught by Professor Rexach during the Fall '10 term at University of California, Santa Cruz.

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Biol110-10-Lecture 16-Mitosis - The mechanics of cell...

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