分子生物学DNA的复制ppt课件.ppt

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1、3．DNAreplicationIncluding3.1Anoverview3.2BacterialDNAreplication3.3EukaryoticDNAreplication3.1Anoverview3.1.1Semi-conservativemechanism3.1.2Replicons,originsandtermini3.1.3Semi-discontinuousreplication3.1.4RNApriming3.1.1Semi-conservativemechanismDuringreplication,thestrandsofthedoublehelixseparated

2、andeachactsasatemplatetodirectthesynthesisofanewcomplementarydaughterstrandfollowingthenormalbase-pairingrules.Thus,eachdaughtercellreceivesoneoftheoriginalparentalstrands.ThepointatwhichseparationofthestrandsandsynthesisofnewDNAtakesplaceisknownasreplicationfork.Thissemi-conservativemechanismcanbed

3、emonstratedexperimentallyin1958byMeselsonandStahl.3.1.2Replicons,originsandterminiAnypieceofDNAwhichreplicatesasasingleunitiscalledareplicon.TheinitiationofDNAreplicationalwaysoccursatafixedpoint---origin.Usually,thereplicationforksproceedbidirectionallyuntilltheteminusisreached.Allprokayoticchromos

4、omesandmanybacteriophageandviralDNAmoleculesarecircularandcomprise(含)singleorigin.Thus,thereisasingleterminationsiteroughly180ooppositetheuniqueorigin.LinearviralDNAusuallyhaveasingleorigin,butthisisnotnecessarilyinthecentreofthemolecules.Incontrast,thelong,linearDNAofeukaryoticchromosomesconsistofm

5、ultiplereplicons,eachwithitsownorigin.Mammalian（哺乳动物）cell,50000-100000repliconsDirectionDNA复制从特定的位置开始，大多数是双向等速复制方向进行的。有一些是单向的；或以不对称的双向方式进行。Bidirectionalreplicationofacircularbacterialrepicon.(P76)Multipleeukaryoticreplicons.Speed真核生物DNA的复制速度比原核生物慢，真核生物复制叉移动速度大约为1000-3000bp/min；细菌DNA50000bp/min，相差约20

6、-50倍。但真核生物染色体DNA上有许多复制起点，可以分段复制。真核生物染色体DNA包含了许多串联排列的复制子，每一个复制子都有一个复制起点，使真核生物染色体的复制实为多复制子的同步复制。复制方式线性DNA双链的复制眼型复制叉生长方式有单一起点的单向及双向和多个起点的双向几种。DNA正在复制的部分在电镜下观察起来犹如一只眼睛，称为复制眼。环状DNA双链的复制：θ型，滚环型和D－环型滚环复制ΦΧ174单向复制D—环复制（D—loop）存在于线粒体和叶绿体，其特点是两条链复制不同步3.1.3Semi-discontinuousreplicationSemi-discontinuousreplica

7、tionmodel.Onestrand,theleadingstrand,ismadecontinuouslyina5'→3'directionfromtheorigin.Synthesisofthesecond,laggingstrandistheninitiatedatthereplicationforkandproceeds5'→3'backtowardstheorigintoformthe