文稿讲稿第六章

Thestructureandfunctionoforganelleswhichareinvolvedinproteinsynthesisprocessingandtransport WhatareProteinsarelargebiologicalmoleculesconsistingofoneormorechainsofaminoacids.Proteinsperformavastarrayoffunctionswithinlivingorganisms,includingcatalyzingmetabolicreactions,replicatingDNA,respondingtostimuli,andtransportingmoleculesfromonelocationtoanother.WhatdeterminetheaminoacidsequenceofProteinsdifferfromoneanotherprimarilyintheirsequenceofaminoacids,whichisdictatedbythenucleotidesequenceoftheirgenes,andwhichusuallyresultsinfoldingoftheproteinintoaspecificthree-dimensionalstructurethatdeterminesitsHowcouldDNAinthecellnucleusernproteinsynthesisintheWhatisproteinsynthesisWhatarethereintheWhatisthefunctionofaThefunctionofthenucleus1、tomaintaintheintegrityofthese2、tocontroltheactivitiesofthecellbyregulatinggeneexpressionThenucleusisthecontrolcenteroftheWhatisheredityWhatisheredityHeredityisabiologicalprocesswhereaparentpassescertaingeneticinformationontotheirchildrenoroffspring.Everychildinheritsgeneticinformationfrombothoftheirbiologicalparentsandtheseinformationinturnexpressspecifictraits.Someofthesetraitsmaybephysicalforexamplehairandeyecolorandskincoloretc.Ontheotherhandsomegeneticinformationmayalsocarrytheriskofcertaindiseasesanddisordersthatmaypassonfromparentstotheiroffspring.AgeneAgeneisamolecularunitofheredityofalivingGeneThetransferofinformationfromDNAtoCentral eticinformationistranscribedfromDNAtoRNAandthentranslatedfromRNAintoprotein.Translationisaprocesswheregeneticinformationistranslatedfroma``nucleicacidlanguage"toan"aminoacidlanguage.Whataretherequiredcomponentsnecessaryforthesynthesisofprotein?Whataretherequiredcomponentsnecessaryforthesynthesisofprotein?mRNAconveygeneticinformationfromDNAtotheribosome ThemRNAcanbeusedasatemplatefordeterminingthecorrectsequenceofaminoacidsinaparticularprotein. eticEachcodonconsistsofthreebaseseachandencodesforaspecificaminoacid 遗 是连续和有方向起 UAA、UAG、简并性（同 遗 在各种生物中是一样Howist eticcodetranslatedintoprotein?tRNAmediatesrecognitionofthecodonandprovidesthecorrespondingaminoacid.thewobblehypothesisAnti-丙氨酰- 3’……CGI

GCU

5’……GCC5’……GCArRNAisthecentralcomponentoftheribosome'sprotein-manufacturingmachineryAribosomeismadefromcomplexesofRNAsandproteinsandisthereforearibonucleoprotein.Eachribosomeisdividedintotwosubunits:thesmallersubunitbindstothemRNApattern,whilethelargersubunitbindstothetRNAandtheaminoWhenaribosomefinishesreadinganmRNAmolecule,thesetwosubunitssplitapart.Ribosomesareribozymes,becausethecatalyticpeptidyltransferaseactivitythatlinksaminoacidstogetherisperformedbytheribosomalRNA.RibosomeprovidesbindingsitesformRNAandtRNA.bindingsitestRNAbindingsites（Psite，Asite，Esite）ThebindingsitesforotherfactorsribosomesribosomesarethesitesofproteinsynthesisTranslationoccursinthecytoplasm,wheretheribosomesarelocated.Ineukaryoticcells,thecytoplasmisthatpartofthecellbetweenthecellmembraneandthenuclearThecytoplasmcomprisescytosol—thegel-likesubstanceenclosedwithinthecellmembrane—andtheorganelles—thecell'sinternalsub-structures,including(ineukaryotecells)thenucleus.ThecytoplasmhasthreemajorCytoplasmicOrganelles("littleorgans"),areusuallymembrane-bound,andarestructuresinsidethecellthathavespecificfunctions.Somemajororganellesthataresuspendedinthecytosolarethemitochondria, reticulum,theGolgiapparatus,vacuoles,lysosomes,andinplantcellschloroplasts.CytoplasmicTheinclusionsaresmallparticlesofinsolublesubstancessuspendedinthecytosol.Ahugerangeofinclusionsexistindifferentcelltypes.Aparticularlywidespreadexamplearelipiddroplets,whicharesphericaldropletscomposedoflipidsandproteinsthatareusedinbothprokaryotesandeukaryotesasawayofstoringlipidssuchasfattyacidsandsterols.Lipiddropletsmakeupmuchofthevolumeofadipocytes,whicharespecializedlipid-storagecells,buttheyarealsofoundinarangeofothercelltypes.Thepartofthecytoplasmthatisnotheldwithinorganellesiscalledthecytosol.Cytosolmakesupabout70%ofthecellvolumeandiscomposedofwater,saltsandorganicmolecules.Thecytosolalsocontainstheproteinfilamentsthatmakeupthecytoskeleton,aswellassolubleproteinsandsmallstructuressuchasribosomes,proteasomes,andthemysteriousvaultcomplexescytoskeletonItiswithinthecytoplasmthatmostcellularactivitiesoccur,suchasmanymetabolicpathwaysincludingglycolysis,andprocessessuchascelldivision.Translationproceedsinfourphases:activation,initiation,elongation,andtermination.Inactivation,thecorrectaminoacid(AA)isjoinedtothecorrecttRNA.acid

initiatio大亚 转进移termination结合子

多肽链释Initiationinvolvesthesmallsubunitoftheribosomebindingto5'endofmRNAwiththehelpofinitiationfactors(IF),otherproteinsthatassisttheprocess.Elongationoccurswhenthenextaminoacyl-tRNAinlinebindstotheribosomealongwithGTPandanelongationfactor.TerminationofthepolypeptidehappenswhentheAsiteoftheribosomefacesastopcodon(UAA,UAG,orUGA).Whenthishappens,notRNAcanrecognizeit,butreleasingfactorcanrecognizenonsensecodonsandcausesthereleaseofthepolypeptidechain.orpolysomeEndoplasmicFreeoplasmicreticulumisanetworkoftubulesandflattenedsacsthatserveavarietyoffunctionsinthecell.TheERisveryextensiveextendingfromthecellmembranethroughthecytoplasmandformingacontinuousconnectionwiththenuclearenvelope.问题oplasmicreticulumisclassifiedintotwotypesreticulum(RER)

reticulum(SER)thesmoothERisatubulenetworkandtheroughERisaseriesofflattenedsacs.信号假Freeandmembrane-boundribosomesdifferonlyintheirspatialdistribution;theyareidenticalinstructure.Whethertheribosomeexistsinafreeormembrane-boundstatedependsonthepresenceofanER-ingsignalsequenceontheproteinbeingsynthesized,soanindividualribosomemightbemembrane-boundwhenitismakingoneprotein,butfreeinthecytosolwhenitmakesanotherprotein.Proteinsthatareformedfromfreeribosomesarereleasedintothecytosolandusedwithinthecell.Boundribosomesusuallyproduceproteinsthatareusedwithintheplasmamembraneorareexpelledfromthecellviaexocytosis.ThenewlyproducedpolypeptidechainsareinserteddirectlyintotheERbytheribosomeandarethentransportedtotheirdestinations,throughthesecretorypathway.Theroughendoplasmicreticulummanufacturesmembranesandsecretoryproteins.Theroleof oplasmicreticuluminproteinprocessingandsorting.Proteinsynthesisandtranslocationthetranslocationreactioninvolves:(a)theidentificationingofproteinstotheER,(b)theassociationofproteinswiththeERtranslocationmachinery,includingaporethroughwhichproteinsentertheER,(c)theenergy-dependentimportofproteinsintotheERlumenormembrane,and(d)proteinfoldingandmaturationintheER2、proteintheproteolyticcleavageofthesignalproteinglycosylation寡聚糖转移 Glycosylation(seealsochemicalglycosylation)isthereactioninwhichacarbohydrateisattachedtoahydroxylorotherfunctionalgroupofanotherThecarbohydratechainsattachedtotheproteinsservevariousfunctions:someproteinsdonotfoldcorrectlyunlesstheyareglycosylatedfirst.polysaccharideslinkedattheamidenitrogenofasparagineintheproteinconferstabilityonsomesecretedglycoproteins.Glycosylationalsoplaysaroleincell-celladhesionviasugar-bindingproteinscalledlectins,whichrecognizespecificcarbohydratemoietiesTypesofglycosylation

N-linked(天冬酰胺的-O-linked(苏氨酸、丝氨酸、N-linkedglycosylationisthemostcommontypeofglycosidicbondandisimportantforthefoldingofsomeeukaryoticproteinsandforcell-cellandcell-extracellularmatrixatta TheN-linkedglycosylationprocessoccursineukaryotesinthelumenof oplasmicreticulumO-linkedglycosylationisaformofglycosylationthatoccursineukaryotesintheGolgiapparatus3.ProteinFolding,assemblyofmultisubunitanddisulfidebondformationinthedisulfidebondAclassoffoldingcatalyst伴侣蛋白（chaperoneprotein）bindstoanascentproteinsastheyemergefromthetranlocon.AbundantchaperonesexistwithinthelumenoftheERthatpromoteproteinfoldingindifferentways.结合AssociatesinanATPdependentprocesswithhydrophobicpeptidesequencesofmostproteinstoshieldhydrophobicresiduesfromwater.theoxidizingenvironmentintheERlumenfavorstheformationofdisulfidebondsImproperlyfoldedproteinsareexportedfromtheERanddegradedinthecytosolERlumenalchaperonesnotonlypreventinappropriateinter-andintra-molecularinteractionsbutalsorecognizeterminallymis-foldedproteinsand themforERassociateddegradation(ERAD)QualityERstressandtheunfoldedproteinEndoplasmicreticulum:aprimary invariousacutedisordersanddegenerativediseasesofthebrainChangesinneuronalcalciumactivityinthevarioussubcellularcompartmentshavedivergenteffectsoncells.Inthecytoplasmandmitochondria,wherecalciumactivityisnormallylow,aprolongedexcessiveriseinfreecalciumlevelsisbelievedtobetoxic,in oplasmicreticulum(ER),incontrast,calciumactivityisrelativelyhighandseverestressiscausedbyadepletionofERcalciumstores.Besidesitsroleincellularcalciumsignaling,theERisthesitewheremembraneandsecretoryproteinsarefoldedandprocessed.Thesecalcium-dependentprocessesarefundamentaltonormalcellfunctioning.UnderconditionsofERdysfunctionunfoldedproteinsaccumulateintheERlumen,asignalresponsibleforactivationoftheunfoldedproteinresponse(UPR)andtheER-associateddegradation(ERAD).UPRischaracterizedbyactivationoftwoER-residentkinases,PKR-likeERkinase(PERK)andIRE1.PERKinducesphosphorylationoftheeukaryoticinitiation(eIF2α),resultinginashut-downoftranslationattheinitiationstep.Thisstressresponseisneededtoblocknewsynthesisofproteinsthatcannotbecorrectlyfolded,andthustoprotectcellsfromtheeffectofunfoldedproteinswhichtendtoformtoxicaggregates.IRE1,ontheotherhand,isturnedafteractivationintoanendonucleasethatcutsoutasequenceof26basesfromthecodingregionofxbp1mRNA.Processedxbp1mRNAistranslatedintotherespectiveprotein,anactivetranscriptionfactorspecificforERstressgenessuchasgrp78.Inacutedisordersanddegenerativediseases,theERcalciumpoolisaprimary oftoxicmetabolitesorintermediates,suchasoxygenfreeradicals,producedduringthepathologicalprocess.AffectedneuronsneedtoactivatetheentireUPRtocopewi