分子生物学Chapter 4 DNA Replication

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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)