molecular biologyDNA序列是遺傳信息的貯

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-編碼鏈（codingstrand）:與mRNA序列相同的那條DNA鏈或稱有意義鏈（sensestrand）.模板鏈 testrand）:根據(jù)堿基互補原則指導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-編碼鏈（codingstrand）:與mRNA序列相同的那條DNA鏈或稱有意義鏈（sensestrand）.模板鏈 testrand）:根據(jù)堿基互補原則指導mRNA合成, te點被稱為position+1。 ThreeThree封閉復合物（closed開放復合物（open三元復合物（ternary?TheinitialbindingofpolymerasetoaDNAremainsdoubleTheenzymeisboundtoonefaceoftheTheDNAstrandseparateoveradistanceof~14bp(-11to+3)aroundthestartsite(+1site)?Transcriptionbubble?TheenzymeescapesfromtheThetransitiontotheelongationStableternarycomplex=DNA+RNA+Terminator:通常含有自我互補區(qū)域(plementaryTwoTwoTypesofTerminatorsinE.不依賴于ρ因子的終止intrinsicterminator(內在由兩個序列原件組其后是一段大約8個A:T堿基對的序列由它轉錄出mRNA可形成莖環(huán)結RNApolWeakestbasepairing:A:Umakethedissociationeasier其終止需要ρ因子的參與ρ因子與ssRNA的特定位點結合(C豐富，G缺乏)ρ通過催化NTP的水解促使新生RNA鏈從三元轉錄復合物中解。ρ因子參與的RNA合成終止模的速度要慢得多（800bp/秒）。 RNA聚合酶(RNA主要以雙鏈DNA為模板，以4種核苷三磷酸作為活性前體需要Mg2+/Mn2+為輔助因子它不需要任何引以5’→3’方向合成RNA缺乏3’→5’外切酶活性是一個含有多個亞單位(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只有一個DNA-directed由5種subunits組成聚合酶全酶(holoenzyme),包括2α,1β,1β’,1ω以及1σsubunits。直接與16bpDNA結合。整個聚合酶可結合60bpDNA。RNA合成速率40nt/秒,°CE.coliRNApolymerase:α 由 E.coliRNApolymerase:β&β’。 E.coliRNApolymerase:σ與σ因子的結合使RNA聚合酶 酶轉變?yōu)榫酆厦溉冈诩毎袑Ζ乙蜃恿康男枨笊儆诰酆厦钢衅渌鼇唵挝淮竽c桿菌中的σ因子的特異間隔6T3和T7噬菌體的RNA聚合酶是由一條小的多肽鏈組成,相對分子量小于1×105；在37oC下，其轉錄速度為200nt/它們只能識別不同于Ecoli酶hnRNA*,snRNA,約*hnRNAheterogeneousmuclearRNA,核內不均一RNA,RNA抑制靶抑制作利福霉細菌全β亞基結合，抑制起鏈霉溶菌細菌β亞基結合，抑制起放射線素真核DNA結合，延α-鵝膏真核RNAPolⅡ結聚合酶聚合酶聚合酶RPARPBRPARPBRPCRPBRPCRPBRPBRPBRPC所RPC所只有一條多肽鏈，相對分子量小于7X104，是已知最小的 PolymeraseBetweenRNA&RNADNA Require40nt/900ExonucleaseSynthesized te真核生物RNA聚合酶不能直接識別的啟動子區(qū)，需要一物(preinitiationtranscriptioncomplex,PIC)以保證有效地起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兩側為C和Ti.e.CGTor啟動子是一段位于結構5’端上游區(qū)的保守的DNA序列，能 PribnowPribnow它和轉錄起始位點一般相距5bp功能RNApol緊密結合使RNApolPribnowBox降突變(downmutation)； (Bindingsite)和起始(Initiationsite)三個位點； Hogness等發(fā)現(xiàn)類似Pribnow區(qū)的Hogness區(qū)，在轉錄起始點上游～–30bp處，保守序列為TATAAA，也稱TATA區(qū)CAAT區(qū)（CAATbox）。 TATAbox–25～–30bp上游啟動子元件（upstreampromoterCAATbox：–70～–80區(qū)CCAAT–啟動子完整性影 表稱遠上游序列（farupstreamsequence）。Anenhancerisanorientation-independentregionofnon-protein-codingDNAinthegenomethatisassociatedwitha