Chapter7蛋白质的合成转运和加工课件.ppt

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1、Chapter7ProteinSynthesis,TranspotationandProcessing蛋白质的合成、转运和加工SynthesisofAminoacyl-tRNAandfunctionsiteofribosome1,SynthesisofAminoacyl-tRNAactivationofaminoacid:活化：aa+ATP+E*Aminoacyl-AMP-E+PPi转移：Aminoacyl-AMP-E+tRNAaa-tRNA+AMP+EAminoacylationoftRNAs•Reactionstep:First,theaminoacyl-tRNASynthetaseatt

2、achesAMPtothe-COOHgroupoftheaminoacidutilizingATPtocreateanaminoacyladenylateintermediate.Then,theappropriatetRNAdisplacestheAMP.Aminoacyl-tRNAsynthetasescatalyzeaminoacid-tRNAjoiningreactionwhichisextremelyspecific.NomenclatureoftRNA-synthetasesandchargedtRNAsAminoacid:serineCognatetRNA:tRNAserCogn

3、ateaminoacyl-tRNAsynthetase:seryl-tRNAsynthetaseAminoacyl-tRNA:seryl-tRNAserThesynthetaseenzymesareeithermonomers,dimersoroneoftwotypesoftetramer.TheycontacttheircognatetRNAbytheinsideofitsL-shapeandusecertainpartsofthetRNA,calledidentityelements,todistinguishthesesimilarmoleculesfromoneanother.Modi

4、fiednuclesidesoftRNAIdentityelementsinvarioustRNAmoleculesIdentityelement:TheyareparticularpartsofthetRNAmolecules.Thesearenotalwaystheanticodonsequence,butbasepairintheacceptorstem.IftheseareswappedbetweentRNAsthenthesynthetasesenzymescanbetrickedintoaddingtheaminoacidtothewrongtRNAAclassItRNAsynth

5、etasecontactstRNAattheminorgrooveoftheacceptorstemandattheanticodon.AclassIIaminoacyl-tRNAsynthetasecontactstRNAatthemajorgrooveoftheacceptorhelixandattheanticodonloop.合成酶具有3个结合位点First,theaminoacidreactswithATPtoformaminoacyl~adenylate,releasingpyrophosphate.Energyforthereactionisprovidedbycleavingt

6、hehighenergybondoftheATP.ThentheactivatedaminoacidistransferredtothetRNA,releasingAMP.tRNA负载氨基酸2,ProofreadingofAminoacyl-tRNAsynthetasesKineticproofreading（动力学校对）Chemicalproofreading（化学校对）Whenasynthetasebindstheincorrectaminoacid,proofreadingrequiresbindingofthecognatetRNA.Itmaytakeplaceeitherbyacon

7、formationchangethatcauseshydrolysisoftheincorrectaminoacyl-adenylate,orbytransferoftheaminoacidtotRNA,followedbyhydrolysisRecognitionofthecorrecttRNAbysynthetaseiscontrolledattwosteps.First,theenzymeh