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Translation翻译.ppt

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DNAA“Simple”EukaryoticGeneProcessingofeukaryoticmRNATranslationalcontrolModelofeukaryoticribosomeSmall&largeribosomalsubunits. ABindingsitefor themRNAispresentonsmallsubunit. Twobindingsites (P&A)bindtRNAsonlargesubunit. Psite–holdsthetRNAcarryingthegrowingpolypeptidechain. Asite–holdsthetRNAwiththenextAAtobeadded. RibosomesholdthemRNAandtRNAstogetherandconnecttheaminoacidsattheAsitetothegrowingpolypeptide.StructureoftRNA Alignseachaminoacidwiththecorrespondingcodon •70-80ntlong •3’endhasthe5’-CCAsequencetowhichaaarelinked •Theoppositeendcontainstheanticodonloop •Containsmodifiedbases ManyRNAViruseshavecappedgenomicRNAssimilartoeukaryotichostmRNAsThreedistinctstagesoftranslation Initiation •Ratelimitingstep •RequireshydrolysisofATPandGTP •ResultsinformationofacomplexcontainingthemRNA,theribosomeandtheinitiatorMet-tRNA A.5’end(Cap)dependentinitiation •Theinitiationcomplexbindstothe5’capstructureandscansina5’to3’directionuntilinitiatingAUGisencountered B.Internalribosomeentry Initiationcomplexbindsupstreamofinitiationcodon•Thefirststepistherecognitionofthe5’capbyeIF4F,whichconsistsofthreeproteins,eIF4E,eIF4GandeIF4A. Capbindingprotein,eIF4E,bindstocap •TheN-terminusofeIF4GbindseIF4EandtheC-terminusbindseIF4A •The40SsubunitbindstoeIF4GviaeIF3The40Scomplexthenscansdownthe5’untranslatedregiontothefirstAUGcodon.RibosomeselectsaminoacylatedtRNA eEF1aandGTPareboundtoaminoacylatedtRNA Ribosomecatalyzesformationofapeptidebond TranslocationisdependentoneEF2andGTPhydrolysis ManyribosomesmaytranslatemRNAssimultaneouslyonthesamestrand. Termination Translationisterminated atoneofthreestopcodons(UAA,UAG&UGA). •TerminationcodonattheAsiteisrecognizedbythereleasefactorinsteadofatRNA •Thereleasefactorbindstheterminationcodon •ThepeptidechainisthenreleasedfollowedbydissociationofthetRNAandtheribosome •The5’enddependentinitiationisstimulatedbythepoly(A)bindingproteinPabp1p,whichinteractswitheIF4G •ThisinteractioncircularizesthemRNAandfacilitatesformationoftheinitiationcomple