BIOLOGY 151 Lecture : Control of the Cell Cycle

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29 Nov 2012
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The rate of cell division can also respond to changes in environmental conditions. These variations in cell-cycle length suggest that the cell cycle is regulation varies among cells and organisms. Mitosis-promoting factor (mpf) is present in the cytoplasm of m-phase cells and induces mitosis in all eukaryotes. The concentration of mpf cyclin increases during interphase, then peaks in m phase before decreasing again. The mpf protein kinase is a cyclin-depenent kinase (cdk) that is active only when bound to the cyclin subunit. Thus, when cyclin concentrations are high, more mpf is active and the target proteins are phosphorylated, inhibiting mitosis. After it binds to cyclin, mpf"s cdk subunit becomes phosphorylated at two sites, rendering it inactive. Late in g2, phase enzymes cause one of the phosphate groups on the cdk subunit to drop off: this dephosphorylation reaction changes mpf"s shape, activating it.

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