Lecture11CellCycleFin

Lecture11CellCycleFin - Mitosis & Cytokinesis...

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Mitosis & Cytokinesis Recommended Reading: MBOC 5e, pages 1069 - 1090 1 Bio 103-Fall 2009 © Steven Gross
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No new protein synthesis after entry into mitosis - better retain proteins required for life immediately after cytokinesis ! Condense chromosomes before trying to separate them - think you can quickly separate many balls of unwound string ? Disassemble nuclear envelope - can you connect chromosomes to the centrosomes while the nuclear envelope is in between them ? Ensure that sister chromatids can be reliably and quickly sorted one per daughter cell - how do you assemble a dynamic scaffold that allows us to move chromosomes ? Ensure that a set of chromosomes and adequate organelles are partitioned to each daughter cell - better make sure that you divide the cell in the right place, and move things appropriately first ! Disassemble the scaffold, reform the nuclear envelope, allow chromatin to reorganize - How to accomplish this without significant new protein synthesis ? 2 Mitosis & cytokinesis - what must the cell accomplish ? Bio 103-Fall 2009 © Steven Gross
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Mitosis & cytokinesis - rush hour in the cell cycle Mitosis - chromosomes separate . Cytokinesis - cell divides . What events take place ? - Centrosomes duplicate (S) and separate (prophase). - Chromosomes condense (prophase). - Scaffolding forms (spindle) to align and help separate chromosomes . - Nuclear envelope removed (prometaphase) - note; yeast and slime-mold use “closed” mitosis, where there is no breakdown of the nuclear envelope. - Chromosomes are aligned on spindle equator (metaphase). - Sister chromatids move to opposite poles of cell (anaphase A). - Cell elongates , cleavage furrow forms (anaphase B). - Cell constricts in middle , nuclear envelope reforms , forms two daughter cells (telophase). 3 Bio 103-Fall 2009 © Steven Gross
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Chromosomes duplicate during interphase (S-phase) A duplicated chromosome following condensation during prophase . The sister chromatids are linked by a single centromere . 4 Bio 103-Fall 2009 © Steven Gross
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The centrosome duplicates during interphase At early G 1 , each animal cell has a single centrosome , composed of two centrioles . g - tubulin is an important component of the centrosome that facilitates nucleation of MTs. Centrosome maturation (driven in part by M-CDK activity) occurs where increasing g - tubulin ring complexes at centrosome allow increased MT nucleation The centrosome is required to form the mitotic spindle . The duplicated pairs of centrioles remain within the single centrosome until onset of mitosis . 5 Bio 103-Fall 2009 © Steven Gross
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Prophase Duplicated centrosomes separate. Each centrosome nucleates one pole of the mitotic spindle. Onset of chromosome condensation. Half-life of MTs decreases from 10 min to 0.5 min. Cell surface markers are internalized.
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Lecture11CellCycleFin - Mitosis & Cytokinesis...

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