Mitotic cyclin dependent kinase cdk mpf is regulated

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mitotic cyclin-dependent kinase (cdk)
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MPF is regulated by phosphorylation too little MPF too much MPF Wee1 is a kinase that phosphorylates a tyrosine residue on mitotic-cdk; this is an inhibitory mark Cdc25 is a phosphatase that removes this inhibitory phosphate and thus activates the complex 22 **Cdc2 is normal in these mutants
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Summary of MPF MPF is a complex of 2 proteins: mitotic cyclin and cdc2/cdk Regulation of both proteins dictates MPF activity Mitotic Cyclin levels increase due to increased synthesis which peaks at metaphase Mitotic Cyclin levels precipitously decrease at late anaphase due to destruction of the protein MPF activity is inhibited by phosphorylation of cdc2/cdk by Wee1 MPF activity is activated by removal of phosphate from cdc2/cdk by cdc25 23
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Other steps of cell cycle modified by cyclin/cdk complexes mid G1- upregulate transcription of late G1 cyclin Late G1- upregulate transcription of factors required for S phase and mitosis *** G1 cyclins regulate the Restriction Point (point of no return) 24
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25 Organized Replication and Separation of Chromosomes
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Microtubules bind to Chromosomes at Kinetochore Middle of chromosomes are specialized regions of DNA called centromeres Cohesins bind 2 centromere together Protein complex called kinetochore connects centromeres to microtubules Binding of MT to both sides gives tension to aid in segregation 26
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Microtubules movements and organization depends on centrosomes Each new daughter cell needs centrosome (MTOC) Bipolar centrosomes essential to proper chromosomal segregation 27
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Dividing cells have 3 types of microtubules Astral point toward cell periphery Kinetochore Bind kinetochore to centrioles Polar Interdigitate all cell center to help push chromosomes apart All originate from centrosome with (-) end at centrosome and (+) end moving away from centrosome 28
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Alignment of chromosomes at metaphase plate requires MT motors Dynein/dynactin at centromeric region pull towards MTOC (-) end of MT spindle (spindle pole) Pulling from both sides b/c chromosomes are linked Kinesins connect chromosome arms to polar MT anchor chromosome to MT beyond the depolymerizing region Growth occurs due to high levels of tubulin = MT treadmilling occurs at centromere
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