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Must be duplicated to allow each cell to receive a centrosomeoForms the “two poles” of the celloAs the 2 centrosome separate, they produce an array of microtubules “the aster”Mitotic spindle assemblyoMicrotubules continuously grow/shrink independent of each otheroDuring M-phase they are actively growing/shrinking from both centrosome, forming “spindle poles”oAt some point they interact with tubules from opposite centrosome and stabilize, forming “interpolar microtubules”oAssembly of this is driven by large motor proteins that crosslink and stabilizePrometaphase- nuclear membrane degrades and kinetochores attach chromosomes to mitotic spindleoBegins with breakdown of nuclear pores and nuclear laminaoSpindle microtubules already being formedoAs nuclear membrane breaks down the spindle gain access to chromosomes and capture thenoSpindle bind via “kinetochores” at centromeres Metaphase- chromosomes line up halfway between poles; anaphase- sister chromatids separateoChromosomes then oscillate back and forth in a “tug of war” towards opposite spindlesChromosome separation triggered by APC*** THIS IS IMPORTANToAPC- anaphase promoting complexoInitiated by release of cohesinsoCatalyzed by “separase”oAPC degrades securing which allows separase to become active which degrades cohesion ringsCytokinesis in plant cells involves formation of a new cell wall, no pinchingOrganelles must divide too!!!!oMitochondira/chloroplast duplicated by division similar to cell divisionoThey are present in large enough numbers to be equally distributed when new cellis formed
oER is continuous with nuclear membrane, it is released from nuclear membrane but remains intactoCut in two during cytokinesisoGolgi is fragmented during M and the fragments associate with the spindle microtubules by motor proteins “hitching a ride” to polesoSoluble proteins in cytoplasm are inherited randomly during cytokinesisApoptosis- programmed cell growtho“cell suicide”- CONTROLLED death process- in response to singalsoAmount of normal apoptosis is cray- ½ of nerve cells during development die anda billion cells in gut and bone marrow cells each dayoOrgan size is regulated by balance between rate of cell birth and rate of cell death!!!!!oApoptosis is quick and clean, and is safe. It’s cleaned up by phagocytes and organic material can be recyclesoNecrosis is messy and is result of injury or inflammationApoptosis regulated by intracellular proteolytic cascadeoCaspases- family of proteasesoInactive “precaspases” cleaved in response to cellular signalsoInitiate caspase “cascades” amplifying the responseoThey then break down nuclear lamina and other cytosolic proteins to “dismantle” the celloIRREVERSIBLE- TIGHTLY CONTROLLEDApoptosis is also regulated by Bcl-2 family of proteinsoDeath when signals release cytochrome C from mitochondria, activating caspasesoSurvival when block caspase activation by blocking release of cytochrome CBak and Bax stimulate formation of the “apoptosome” NEED TO KNOW THIS!