Chapter 14 Notes -Lecture 17 and 18 (2012)

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Biological Sciences
Dan Riggs

Chapter 14 Notes BIOB11 Prophase Lecture 17Cell Cycle II Chromosome condensation and movement Events of Mitosis Overview of Critical Steps Prophase chromosomes condense chromatids are visiblecytoskeleton disassembles spindle apparatus forms nuclear membrane breaks downPrometaphase chromosomes are captured by MTs at centromerekinetochores and begin movement to equatorMetaphasechromosomes aligned on metaphase plate after this point there is a checkpointAnaphasesister chromatids separate begin poleward movementpoles also more apart Telophasechromosomes cluster at opposite poles decondense nuclear membrane reformsCyclinCDK Complexes Promote Cell Cycle Progression we know that in the cell cycle cyclin dependent kinases CDKSTART is when G1 cyclinCDK triggers transition from G1 to S phaseexperiment showed that there is a factor in the cytoplasm that triggers cell division this wascalledMaturation Promoting Factor MPF was this factor in the cytoplasm and it was shown that the active form of MPF in Mphase has 1 A subunit that has cyclindependent kinase2 Cyclin subunit needed for the kinase activity Maturation Promoting Factor MPF Mitotic cyclin is a type of MPF mitotic cyclinCKD triggers transition from G2 to M phasewhat are the targets of these protein kinasesThe Targets of MPF we know that during S phase 1 DNA replication initiates 2 Centrioles are replicatedFor M phaseto occur1 Nuclear membrane breaks down lamins must be broken down we know the inner surface of the nuclear envelope is made up of nuclear lamina this is the mechanical support and also the attachment site for chromatin fibers at nuclear periphery the lamina are made of polypeptides laminsthe integrity of these lamins is regulated by phosphorylation and dephosporylation this is induced prior to mitosis by phosphorylation of the lamins by MPF2 Chromosomes condense condensingcohesin the very long chromatin fibers must undergo chromosome compaction or condensation to segregate in M phase the much shorter thicker structures are made of similar types of fibersand this does not alter the nature of it only the way its packaged when the histones are solubilized reveals a scaffold that has basic shape loops of DNA are attached at base to the protein that makes up this scaffold in interphase these proteins are dispersedpart of the mitotic chromosome scaffold is condensinthe multiprotein complex Condensin helps with chromosome compaction It can in the presence of ATP bind to DNA and curl it into positively supercoiled loops
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