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Review part 2 complete review for the second part of the course

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James Fenwick

BIO 1140 PART II REVIEW MICROTUBULESLargest of the cytoskeletal elements at 25 nm in diameterOriginate from an MTOC microtubule organizing centre ex Centrosome in animals MTOC are sometimes oddly placed embedded in inside of nuclear membrane in fungiCan push and pull things by growth Structure TubulinOnly made up of one protein called tubulinThere are three types of tubulin alpha beta and gammaAlpha and beta tubulin form alphabeta tubulin dimers basic subunit of microtubulesGamma tubulin is found in MTOCAlpha tubulin is associated with GTP which is NOT hydrolysed found at ring of minus end does not exchangeBeta tubulin is associated with GTP and CAN be hydrolysed found at ring of plus end can be exchanged Each alpha and beta tubulin have GTP binding domain at N terminus domain in middle to which MT poison colchicines can bind and third domain at C terminus that interacts with MT associated proteinsAll dimers are oriented in same direction where alpha faces the end General StructureThese heterodimers of alphabeta tubulin polyermize to form protofilametns13 protofilaments fold over to form a hollow tubeThese are all parallel FunctionCell shape and movementsSeparation of chromosomesTransport of organellesSome forms of cell locomotion Two Basic Types of Microtubules 1 Cytoplasmic microtubules loosely organized in cytoplasm but dynamic networkThey are responsible for shape form mitoticmeiotic spindles and guide movement and placement of organelles 2 Axonemal microtubules form subcellular structures for cellular movement ie cilia and flagella PolymerizationPolarity determines direction microtubules growGTP increases polymerization whereas GDP reduces affinity therefore decreases itAssembly 1 nucleationdimers aggregate into oligomeres 2 oligomeres form protfilaments 3 protofilaments line up to form sheets 4 when sheet has 13 protfilaments it folds into cylinder 5 elongation continues at the ends Each heterodimer binds to two GTP growing MTs have GTP bound to plus end shrinking end with GDP PoisonsColchicines poison that prevents microtubule assemblyTaxol anticancer agent but for microtubules it stabilizes them Microtubular Associated Proteins MAPs Non motor MAPsControl microtubular organization they control direction and pattern of growthWithout MTs wouldnt form spontaneouslyTau family binds to site of MTEx tau MAP2 and MAP4promote assembly when dephosphorylated MAPS or Motor ProteinsKinesin and Dynein Motor Proteins
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