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ID:38338141
大小:1.43 MB
页数:37页
时间:2019-06-10
《分子生物学Chapter 4 DNA Replication》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、Chapter4DNAReplicationIntroductionTheWatson-CrickduplexstructureofDNAimmediatelysuggestedhowgeneticmaterialwasduplicatedfromonegenerationtothenext.TherealizationthatbacterialgenomesandeukaryoticchromosomesconsistofsingleDNAmoleculesmillimeterstocentimetersinlengthraisedah
2、ostofstructuralandbiochemicalquestionsaboutDNAreplication.Howdoesreplicationbegin?WhichenzymestakepartinDNAsynthesis,andwhataretheirfunctions?Howdoesduplicationofthelonghelicalduplexoccurwithoutthestrandsbecomingtangled?Aswewillsee,tocarryoutDNAreplication,allcellsusethes
3、amekindsofenzymes,includingDNApolymerases,whichassembledeoxyribonucleotidesintoanewstrand;helicases,whichunwindduplexDNA;single-strandedDNA-bindingproteins;andexonucleases.BacteriaandyeastcontainthreedifferentDNApolymerases,andmammaliancellscontainfive.Eachtypeofpolymeras
4、ehasuniquefunctionsduringDNAreplicationandrepair.Additionally,someoftheenzymesthatcutandrepairdamagedDNAalsoparticipateingeneticrecombination.Anothercommonfeatureofthethreeprocessesdiscussedinthischapterisinvolvementoflargemultisubunitcomplexes,eachcontainingmanyenzymesan
5、dstructuralproteins.ThesemolecularmachineshaveevolvedtoensurethatDNAreplication,repair,andrecombinationoccurveryrapidlyandwithexquisiteprecision.Autoradiographicanalysescarriedoutintheearly1960sonwholereplicatingchromosomeslabeledwithashortpulseoftheradioactiveDNAprecurso
6、r3H-thymidinerevealedalocalizedregionofreplicationthatmovesalongtheparentalDNAdoublehelix.BecauseofitsY-shapedstructure,thisactiveregioniscalledaDNAreplicationfork.AtareplicationforktheDNAofbothnewdaughterstrandsissynthesizedbyamultienzymecomplexthatcontainstheDNApolymera
7、se.Figure4-1ThereplicationforkistheregionofDNAinwhichthereisatransitionfromtheunwoundparentalduplextothenewlyreplicateddaughterduplexes.(AnimatedFigure)1.GeneralFeaturesofChromosomalReplicationOneSentenceStatement:DNAreplicationproceedsSequentiallyandSemi-Discontinuouslyf
8、romoneormoreUnique,HeritableOrigin(s)atone(UniDirectional)ortwo(BiDirectional)replicationFork(s)
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