molecular biologyDNA序列是遗传信息的贮

Lesson123DNADNA4CentralDogma 5 678SecondarySecondaryStructureofRNAchainsfoldbackontoformlocalregionsofdouble9TheDoubleHelicalStructureofRNAstructureislesswellsuitedforsequence-specific ctionswithproteins.PseudoknotsarecomplexstructureresultedfrombasepairingofdiscontinuousRNAsegmentsWobbleBaseWobblebasepairisanon-Watson-CrickbasepairingbetweentwonucleotidesinRNAWobblebasepairsarefundamentalinRNAsecondarystructureandarecriticalforthepropertranslationofthegeneticFunctionsofFunctionsinproteinmRNA:astheintermediatebetweenthegeneandtheprotein-synthesizingmachinery.tRNA:asanadaptorbetweenthecodonsinthemRNAandamino yastructuralrole,asinthecaseoftheRNAcomponentsoftheribosome.AsgeneticServingasa teforitsownreplicationin RNAascatalystsSomeRNAs(includingoneofthestructuralRNAsoftheribosome)areenzymesthatcatalyzeessentialreactionsinthecell.RNAisaregulatorySmallnoncodingRNAwhichthroughsequencecomplementarilybindsto,andinterfereswiththetranslationofcertainmRNAs.ReplicationvsReplication:synthesisoftwoDNAstrandsusingbothparentalDNAstrandsastem tes.DuplicationofaDNAmolecule1DNAmolecule→2DNATranscription:synthesisofoneRNAmoleculeusingoneofthetwoDNAstrandsasatem TranscriptionischemicallyandenzymaticallyverysimilartoDNADifferenceBetweenRNAandRNAismadeofRNApolymerasecatalyzesthereaction,whichdoesnotrequireaprimer.TheRNAproductdoesnotremainbase-pairedtothe teDNAstrand.Lessaccurate(errorrate:10-TranscriptionThelengthofthebubbleis~12-14bp,andthelengthofRNA-DNAhybridwithinitis~8-9bp.DNA–mRNA-编码链（codingstrand）:与mRNA序列相同的那条DNA链或称有意义链（sensestrand）.模板链 testrand）:根据碱基互补原则指导mRNA合成,TranscriptionUnitAtranscriptionunitisasequenceofDNAtranscribedintoasingleRNA,startingatthepromoterandendingattheterminator.ofRNApolymerasesareenzymesthatsynthesizeRNAusingaDNAtem te(formallydescribedasDNA-dependentRNApolymerases).PromoterisaregionofDNAwhereRNApolymerasebindstoinitiatetranscription.Startpoint(Startsite)referstothepositiononDNAcorrespondingtothefirstbaseincorporatedintoRNA.TerminatorisasequenceofDNAthatcausesRNApolymerasetoterminatetranscription.TranscriptionunitisthedistancebetweensitesofinitiationandterminationbyRNApolymerase.ofofUpstreamidentifiessequencesproceedingintheoppositedirectionfromexpression;forexample,thebacterialpromoterisupstreamofthetranscriptionunit,theinitiationcodonisupstreamofthecodingregion.Downstreamidentifiessequencesproceedingfartherinthedirectionofexpression;forexample,thecodingregionisdownstreamoftheinitiationcodon.PrimarytranscriptistheoriginalunmodifiedRNAproductcorrespondingtoatranscriptionunit.HowdoesRNApolymerasefindpromotersonDNA?(howdoproteinsdistinguishtheirspecificbindingsitesinDNAfromothersequences?)Howdoregulatoryproteinsin ctwithRNApolymerasetoactivateortorepressspecificstepsintheinitiation,elongation,orterminationoftranscription?RNARNA必需的成分:RNApolymerase,rNTPs,transcriptionfactors,promoter&terminator/tem DNA–mRNA-编码链（codingstrand）:与mRNA序列相同的那条DNA链或称有意义链（sensestrand）.模板链 testrand）:根据碱基互补原则指导mRNA合成, te点被称为position+1。 ThreeThree封闭复合物（closed开放复合物（open三元复合物（ternary•TheinitialbindingofpolymerasetoaDNAremainsdoubleTheenzymeisboundtoonefaceoftheTheDNAstrandseparateoveradistanceof~14bp(-11to+3)aroundthestartsite(+1site)•Transcriptionbubble•TheenzymeescapesfromtheThetransitiontotheelongationStableternarycomplex=DNA+RNA+Terminator:通常含有自我互补区域(plementaryTwoTwoTypesofTerminatorsinE.不依赖于ρ因子的终止intrinsicterminator(内在由两个序列原件组其后是一段大约8个A:T碱基对的序列由它转录出mRNA可形成茎环结RNApolWeakestbasepairing:A:Umakethedissociationeasier其终止需要ρ因子的参与ρ因子与ssRNA的特定位点结合(C丰富，G缺乏)ρ通过催化NTP的水解促使新生RNA链从三元转录复合物中解。ρ因子参与的RNA合成终止模的速度要慢得多（800bp/秒）。 RNA聚合酶(RNA主要以双链DNA为模板，以4种核苷三磷酸作为活性前体需要Mg2+/Mn2+为辅助因子它不需要任何引以5’→3’方向合成RNA缺乏3’→5’外切酶活性是一个含有多个亚单位(multi-subunit)的酶原核生物(原核生物(E.coli)的RNACore2alpha(α)subunit,1beta(β)subunit,1betaprime(β’)1omega(ω)1sigma(σ)原核生物(原核生物(E.coli)的RNAEcoli只有一个DNA-directed由5种subunits组成聚合酶全酶(holoenzyme),包括2α,1β,1β’,1ω以及1σsubunits。直接与16bpDNA结合。整个聚合酶可结合60bpDNA。RNA合成速率40nt/秒,°CE.coliRNApolymerase:α 由 E.coliRNApolymerase:β&β’。 E.coliRNApolymerase:σ与σ因子的结合使RNA聚合酶 酶转变为聚合酶全酶在细胞中对σ因子量的需求少于聚合酶中其它亚单位大肠杆菌中的σ因子的特异间隔6T3和T7噬菌体的RNA聚合酶是由一条小的多肽链组成,相对分子量小于1×105；在37ºC下，其转录速度为200nt/它们只能识别不同于Ecoli酶hnRNA*,snRNA,约*hnRNAheterogeneousmuclearRNA,核内不均一RNA,RNA抑制靶抑制作利福霉细菌全β亚基结合，抑制起链霉溶菌细菌β亚基结合，抑制起放射线素真核DNA结合，延α-鹅膏真核RNAPolⅡ结聚合酶聚合酶聚合酶RPARPBRPARPBRPCRPBRPCRPBRPBRPBRPC所RPC所只有一条多肽链，相对分子量小于7X104，是已知最小的 PolymeraseBetweenRNA&RNADNA Require40nt/900ExonucleaseSynthesized te真核生物RNA聚合酶不能直接识别的启动子区，需要一物(preinitiationtranscriptioncomplex,PIC)以保证有效地起RNApol13122 CTDphosphorylationAtthefirststep,beforetranscriptioninitiation,thepromoterDNAisopenedinthepreinitiationcomplex.Atthesecondstep,DNAopeningexpandstodownstreamduringtranscriptioninitiation.Atthethirdstep,PolIIformsanelongationcomplexandmovesdownstreamtogetherwithopenedDNAposition.B,TFIIB;D,TFIID;E,TFIIE;F,TFIIF;H,TFIIH;PolhypophosphorylatedPolII;PolIIO,phosphorylatedPolII. 通常在起始核苷酸的两侧为C和Ti.e.CGTor启动子是一段位于结构5’端上游区的保守的DNA序列，能 PribnowPribnow它和转录起始位点一般相距5bp功能RNApol紧密结合使RNApolPribnowBox降突变(downmutation)； (Bindingsite)和起始(Initiationsite)三个位点； Hogness等发现类似Pribnow区的Hogness区，在转录起始点上游～–30bp处，保守序列为TATAAA，也称TATA区CAAT区（CAATbox）。 TATAbox–25～–30bp上游启动子元件（upstreampromoterCAATbox：–70～–80区CCAAT–启动子完整性影 表称远上游序列（farupstreamsequence）。Anenhancerisanorientation-independentregionofnon-protein-codingDNAinthegenomethatisassociatedwitha