Must be duplicated to allow each cell to receive a centrosome o Forms the two

Must be duplicated to allow each cell to receive a

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Must be duplicated to allow each cell to receive a centrosome o Forms the “two poles” of the cell o As the 2 centrosome separate, they produce an array of microtubules “the aster” Mitotic spindle assembly o Microtubules continuously grow/shrink independent of each other o During M-phase they are actively growing/shrinking from both centrosome, forming “spindle poles” o At some point they interact with tubules from opposite centrosome and stabilize, forming “interpolar microtubules” o Assembly of this is driven by large motor proteins that crosslink and stabilize Prometaphase- nuclear membrane degrades and kinetochores attach chromosomes to mitotic spindle o Begins with breakdown of nuclear pores and nuclear lamina o Spindle microtubules already being formed o As nuclear membrane breaks down the spindle gain access to chromosomes and capture then o Spindle bind via “kinetochores” at centromeres Metaphase- chromosomes line up halfway between poles; anaphase- sister chromatids separate o Chromosomes then oscillate back and forth in a “tug of war” towards opposite spindles Chromosome separation triggered by APC*** THIS IS IMPORTANT o APC- anaphase promoting complex o Initiated by release of cohesins o Catalyzed by “separase” o APC degrades securing which allows separase to become active which degrades cohesion rings Cytokinesis in plant cells involves formation of a new cell wall, no pinching Organelles must divide too!!!! o Mitochondira/chloroplast duplicated by division similar to cell division o They are present in large enough numbers to be equally distributed when new cell is formed
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o ER is continuous with nuclear membrane, it is released from nuclear membrane but remains intact o Cut in two during cytokinesis o Golgi is fragmented during M and the fragments associate with the spindle microtubules by motor proteins “hitching a ride” to poles o Soluble proteins in cytoplasm are inherited randomly during cytokinesis Apoptosis- programmed cell growth o “cell suicide”- CONTROLLED death process- in response to singals o Amount of normal apoptosis is cray- ½ of nerve cells during development die and a billion cells in gut and bone marrow cells each day o Organ size is regulated by balance between rate of cell birth and rate of cell death!!!!! o Apoptosis is quick and clean, and is safe. It’s cleaned up by phagocytes and organic material can be recycles o Necrosis is messy and is result of injury or inflammation Apoptosis regulated by intracellular proteolytic cascade o Caspases- family of proteases o Inactive “precaspases” cleaved in response to cellular signals o Initiate caspase “cascades” amplifying the response o They then break down nuclear lamina and other cytosolic proteins to “dismantle” the cell o IRREVERSIBLE- TIGHTLY CONTROLLED Apoptosis is also regulated by Bcl-2 family of proteins o Death when signals release cytochrome C from mitochondria, activating caspases o Survival when block caspase activation by blocking release of cytochrome C Bak and Bax stimulate formation of the “apoptosome” NEED TO KNOW THIS!
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