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1、第1节细胞增殖有丝分裂英文版介绍(Mitosis) Mitosisistheprocessinwhichaeukaryoticcellseparatesthechromosomesinitscellnucleus,intotwoidenticalsetsintwodaughternuclei.Itisgenerallyfollowedimmediatelybycytokinesis,whichdividesthenuclei,cytoplasm,organellesandcellmembraneintotwoda
2、ughtercellscontainingroughlyequalsharesofthesecellularcomponents.Mitosisandcytokinesistogetherdefinethemitotic(M)phaseofthecellcycle-thedivisionofthemothercellintotwodaughtercells,geneticallyidenticaltoeachotherandtotheirparentcell.Mitosisdividesthechromosomes
3、 Mitosisoccursexclusivelyineukaryoticcells,butoccursindifferentwaysindifferentspecies.Forexample,animalsundergoan"open"mitosis,wherethenuclearenvelopebreaksdownbeforethechromosomesseparate,whilefungisuchasAspergillusnidulansandSaccharomycescerevisiae(yeast)un
4、dergoa"closed"mitosis,wherechromosomesdividewithinanintactcellnucleus.Prokaryoticcells,whichlackanucleus,dividebyaprocesscalledbinaryfission. Theprocessofmitosisiscomplexandhighlyregulated.Thesequenceofeventsisdividedintophases,correspondingtothecompletionofo
5、nesetofactivitiesandthestartofthenext.Thesestagesareprophase,prometaphase,metaphase,anaphaseandtelophase.Duringtheprocessofmitosisthepairsofchromosomescondenseandattachtofibersthatpullthesisterchromatidstooppositesidesofthecell.Thecellthendividesincytokinesis,
6、toproducetwoidenticaldaughtercells. Becausecytokinesisusuallyoccursinconjunctionwithmitosis,"mitosis"isoftenusedinterchangeablywith"mitoticphase".However,therearemanycellswheremitosisandcytokinesisoccurseparately,formingsinglecellswithmultiplenuclei.Thisoccur
7、smostnotablyamongthefungiandslimemoulds,butisfoundinvariousdifferentgroups.Eveninanimals,cytokinesisandmitosismayoccurindependently,forinstanceduringcertainstagesoffruitflyembryonicdevelopment.Errorsinmitosiscaneitherkillacellthroughapoptosisorcausemutationsth
8、atmayleadtocancer.Phasesofcellcycleandmitosis Interphase Themitoticphaseisarelativelyshortperiodofthecellcycle.Italternateswiththemuchlongerinterphase,wherethecellpreparesitselff
