Summary1.Prokaryoticchromosome:closed-circularDNAdomains/loops,negativelysupercoiled,hUH-Ns2.Eukaryoticchromatin:Histones(octamer:H2A,H2BH3,H4)+146bpDNA>Nucleosomes+hi>chromatosomeLinkerDnabeadsonstring>30nmfiber>fiberloop+nuclearmatrix>highlyorderedchromatin>>>chromosome3.Eukaryoticchromosomestructure:centromere,telomere,hetero-oreuchromatin,CpGislandandmethvlation第五章DNA復制DNAReplicationpeyuusfragmentLasn玻andHHHiHHHtirNuceotidesaddedcontinuouslyto3'end●NAreplicationE:DNA復制概述DNAReplication:AnOverview1.復制子Replicons2.半保留機制semi-onservativemechanism3.半不連續復制semi-discontinousreplication4.RNA引導RNApriming●DNAreplicationE1-1復制子Replicons復制子:以單一單位復制的任一段DNA,含有一個起始點及終點。RepliconisanypieceofdNawhichreplicatesasasingleunit.Itcontainsanoriginandsometimesaterminus起始點OriginistheDNAsequencewherearepliconinitiatesitsreplication終點TerminusisthedNasequencewherearepliconusuallystopsitsreplication●DNAreplication原核生物基因組為單一環狀DNA分子=單一復制子Prokaryoticgenome:asinglecircularDNA=asinglereplIcon真核生物具有多條線性染色體且每條上有多個復制子Eukaryoticgenome:multiplelinearchromosomesmultiplerepliconsoneachchromosome●DNAreplication環形細菌復制子的雙向復制Bidirectionalreplicationofacircularbacterialreplicon所有原核生物染色體,噬菌體及病毒DNA分子都呈環形且只有單一復制子Allprokaryoticchromosomesandmanybacteriophageandviraldnamoleculesarecirclularandcomprisesinglereplicons在與唯一起點相對180處有單一終點Thereisasingleterminationsiteroughly180oppositetheuniqueorigin●DNAreplication線性病毒DNA分子通常有單一的起始點LinearviralDNamoleculesusuallyhaveasingleorigin不管怎樣,起始點都是一個復雜的區域,DNA復制起始及生物生長周期調節都在此調控協調nallthecases,theoriginisacomplexregionwheretheinitiationofDNAreplicationandthecontrolofthegrowthcycleoftheorganismareregulatedandco-ordinated.●DNAreplication多復制子及復制泡Multipleeukaryoticrepliconsandreplicationbubbles真核生物的長的線性染色體由多復制子構成,每個復制子都有自己的起始點DNAThelong,linearDNAmoleculesofeukaryoticchromosomesconsistofmutipleregions,eachwithitsownInorgI典型的哺乳動物細胞有5000010000個復制子,每個長約40200kb。在相鄰復制叉的復制泡相遇處,新生DNA融合成復制完整的DNA。atypicalmammaliancellhas50000-100000repliconswithasizerangeof40-200kb.Whenreplicationforksfromadjacentreplicationbubblesmeet,theyfusetoformthecompletelyreplicatedDNA.Nodistinctterminiarerequired●①replicationreplicationbubblestreplicationforkSeePage71,73ofyourtextbook●DNAreplicationE1-2半保留復制semiconservationreplicationDNA由兩條螺旋的多核苷酸鏈組成,兩條鏈的堿基通過A:T和G:C之間的氫鍵聯結在一起。在復制過程中首先兩條鏈間的氫鍵破裂并使雙鏈解旋和分開,然后以每條鏈為模板,按堿基互補配對原則(A:T,G:C),由DNA聚合酶催化合成新的互補鏈,結果由一條鏈成為互補的兩條鏈,這樣新形成的兩個DNA分子與原來的D