资源描述：
《生物专业英语(9)分析解析备课讲稿.ppt》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、生物专业英语(9)分析解析Incellswithanucleus(eukaryotes),thecellcyclecanbedividedintwoperiods:Interphase—duringwhichthecellgrows,accumulatingnutrientsneededformitosisandduplicatingitsDNA.Themitosis(M)phase,duringwhichthecellsplitsitselfintotwodistinctcells,oftencalled"daughtercells"andthefinalphase
2、,cytokinesis,wherethenewcelliscompletelydivided.Thecell-divisioncycleisavitalprocessbywhichasingle-celledfertilizedeggdevelopsintoamatureorganism,aswellastheprocessbywhichhair,skin,bloodcells,andsomeinternalorgansarerenewed.Beforeacellcanentercelldivision,itneedstotakeinnutrients.Alloft
3、hepreparationsaredoneduringtheinterphase.Interphaseproceedsinthreestages,G1,S,andG2.Celldivisionoperatesinacycle.Therefore,interphaseisprecededbythepreviouscycleofmitosisandcytokinesis.Interphaseisalsoknownaspreparatoryphase,inthisstagenucleusandcytosoldivisiondoesnotoccur.Thecellprepar
4、estodivide.InterphaseG1PhaseThefirstphasewithininterphase,fromtheendofthepreviousMphaseuntilthebeginningofDNAsynthesisiscalledG1(Gindicatinggap).Itisalsocalledthegrowthphase.Duringthisphasethebiosyntheticactivitiesofthecell,whichhadbeenconsiderablysloweddownduringMphase,resumeatahighrat
5、e.Thisphaseismarkedbytheuseof20aminoacidstoformmillionsofproteinsandlateronenzymesthatarerequiredinSphase,mainlythoseneededforDNAreplication.DurationofG1ishighlyvariable,evenamongdifferentcellsofthesamespecies.Itisunderthecontrolofthep53gene.SPhaseTheensuingSphasestartswhenDNAsynthesisc
6、ommences;whenitiscomplete,allofthechromosomeshavebeenreplicated,i.e.,eachchromosomehastwo(sister)chromatids.Thus,duringthisphase,theamountofDNAinthecellhaseffectivelydoubled,thoughtheploidyofthecellremainsthesame.Duringthisphase,synthesisiscompletedasquicklyaspossibleduetotheexposedbase
7、pairsbeingsensitivetoexternalfactorssuchasanydrugstakenoranymutagens(suchasnicotine).G2PhaseThecellthenenterstheG2phase,whichlastsuntilthecellentersmitosis.Again,significantbiosynthesisoccursduringthisphase,mainlyinvolvingtheproductionofmicrotubules,whicharerequiredduringthepro
