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BIOLOGY 2B03 (285)
Kim Dej (39)
Lecture 10

Lecture 10 Summary

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Kim Dej

Lecture 10 SummaryEntry into mitosisneed activated MPF Exit of mitosis requires decrease in mitotic cyclins and inactivation of MPFEarly Mitosis Late mitosis Targets of phosphorylation Targets of phosphatasesMPF active Cyclin degraded mpf inactiveNuclear envelope proteins Nuclear envelope proteins Nuclear pore proteins breakdownNuclear pore proteins Chromosomes condenseChromosome condensation proteins Chromatid cohesion proteinsCohesion proteinsMitotic spindle proteins Mitotic spindle proteins Anaphase separation of sister chromatids Telophase chromosomes decondense nuclear envelope reforms mitotic spindle disassembles and cytokinesisALL regulated by the dephosphorylationdegradation of cyclin B and anaphase inhibitors of proteinsChromosome Condensation Chromosome decondensationChromosome condensation at prophase requires proteins Chromosome decondensation requires dephosphorylation condensins creates loop within dna strands and 1 activity of phosphatases 2 absence of kinase Therefore topoisomerase II keeps DNA untangled Both induce DNA we need to inhibit cyclinBcdksupercoiling Condensins and topoisomerase II are activatedon the onset of prophase by phosphorylation via cyclincdksExpt Degradation of Cyclin B vs Nondegradable cyclin B In nondegradable cyclin Bchromosomes remain condensed after 80 minutes Because cyclin doesnt degrade MPF kinase activity doesnt decrease either And because kinase activity is present the activity of the phosphatases needed to decondense chromosomes is inhibited APCCdh1 targets cyclin B for degradation Cdc14 phosphatase dephosphorylates APCcdh1 making it activecausing cyclin B degradation Degradation of cyclin Bdecrease in MPF activityexit mitosisCohesion molecules associate replicated DNA molecules from S phase to anaphase In vertebrates cohesion molecules are released in 2 ways 1 Chromosomearms bulk of cohesion molecules dissociate from the chromosome arms due to the its phosphorylation by kinases which releases them 2 Centromere the cohesions are cleaved releasing the sister chromatids How are they cleaved The degradation of securin an anaphase inhibitor that is phosphorylated by APCCdc20 for recognition by a proteasome causes the activation of seperase which causes the proteolysis of cohesion molecules releasing sister chromatidsExpt Does APC have any other targets Yes anaphase inhibitorCyclin Ba target for APC Destruction box peptide sequence on the Cyclin B also a target for APC So add untreated extract cyclin B destruction peptide sequence in increasing concentrations Excess peptide acts as competition for normal targets Thus delayingpreventing their degradation15 minute reaction timeanaphase occurs at 0ugml35 minute reaction timeanaphase occurs at 40 ugmlat this point a possible explanation is that the cyclin destruction boxes were all degraded successfully so the APC can now focus on degrading cyclin B alone The degradation of cyclin B allows us to see anaphaseLate anaphaseinactivation of MPF due to degradation of mitotic cyclin Bphosphatase Cdc14 reverses effects of MPF Nuclear Envelope DisassemblyNuclear Envelope Assembly
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