复旦细胞生物学课件10细胞核和染色体

Chap10NucleusandChromosomes•NucleusofaEukaryoticCell•NuclearEnvelope•NuclearPoreComplex•Chromatin•NucleolusandRibosomeBiogenesis•NuclearMatrix8.1TheNucleusofaEukaryoticCellTheinnernuclearmembraneTheouternuclearmembraneSurroundedbytwoconcentricmembranes8.1.1OrganizationoftheNucleuschromosomesnuclearmatrixnucleolinucleoplasmaninterphaseHeLacellnucleusshowingsomeofthemajorcomponentsofthenucleus8.1.2InternalArchitecturecontrasttothecytoplasm,thenucleus:❖notindividuallyenclosedbymembranes❖notvisibleusingconventionallightorelectronmicroscopytechniquesrevisedpictureofnuclearstructure•Nuclearmatrix:aproteinaceousscaffold-likenetwork•Nucleolus:thecenterforsynthesisandprocessingofrRNAmolecules8.2TheNuclearEnvelope•Theseparationofacell’sgeneticmaterialfromthesurroundingcytoplasmmaybesinglemostimportantfeaturethatdistinguisheseukaryotesfromprokaryotes.Structureofthenuclearenvelope•outernuclearmembrane•innernuclearmembrane•nuclearlamina•perinuclearspace•nuclearporenuclearlaminaFunctionofthenuclearenvelopeabarrierbetweenthenucleusandcytoplasm,asadistinctbiochemicalcompartmentsolechannelsthroughthenuclearenvelope8.3NuclearPoreComplex•Vertebrate:50100proteins•Diameter:120nm,125MDa•basketlikeapparatus•eightfoldsymmetryCompositionoftheNPC•Cytoplasmicring•Nuclearring•Spoke•CentralplugNuclearenvelopesofXenopusoocytesvisualizedbyfieldemissionin-lensSEMCut-awaymodeloftheNPCThree-dimensionalmodelsoftheNPCAstructurewitheightfoldsymmetryTheNPCconsistsofanassemblyofeightspokesarrangedaroundacentralchannelThespokesareconnectedtoringsatthenuclearandcytoplasmicsurfacesElectronmicrographofNPCNLSsdirectnuclearproteinstothenucleusThenuclearproteinsareselectivetrafficacrossthenuclearenvelopefromthecytoplasmtothenucleusTheNLSsincludehistones,DNApolymerases,RNApolymerases,transcriptionfactors,splicingfactorstransportthroughNPC核孔运输特点◆被动运输◆主动运输●信号引导●双向性MoleculartrafficthroughNPC核孔的被动运输SmallmoleculartrafficthroughtheNPCbypassivediffusionSmallmoleculesandsomeproteinswithMW50kDpassfreelyacrossthenuclearenvelopeineitherdirection.MostproteinsandRNAspassthroughtheNPCbyanactiveprocessinonlyonedirection.核孔的双向运输mRNA的输出2.1核蛋白运输机制基本概念◆核蛋白(nuclearprotein)◆核定位信号(nuclearlocalizationsignals,NLS)◆核输出信号(nuclearexportsignals,NES)◆输入蛋白(importin)◆输出蛋白(exportin)核定位信号Nuclearlocalizationsignals核蛋白的输入◆核质蛋白(nucleoplasmin)实验◆核蛋白输入机理●输入蛋白●Ran蛋白:小GTPaseRanGAP:RanGTP激活蛋白:细胞质中RCC1：Rannucleotide-exchangefactor1.细胞核中核质素的核定位信号及其作用ReceptorsfortheNLStransportproteinstothenucleusProteinimportthroughtheNPCcanbedividedintotwosteps,distinguishedbywhethertheyrequireenergy.Thefirststepdoesnotrequireenergy,proteinsthatcontainNLSsbindtotheNPCbutdonotpassthroughthepore.Thesecondstepisanenergy-dependentprocessthatrequiresGTPhydrolysis.ProteinimportthroughNPCRoleoftheRanproteininnuclearimport核蛋白输入机理核内RNA与蛋白质输出◆mRNA的输出●异质核糖核蛋白(heterogeneousribonucleoprotein,hnRNP)●信使RNP(messengerRNP,mRNP)●mRNA的输出◆核内蛋白质输出◆snRNA的输出TransportofRNAbetweennucleusandcytoplasm•active,energy-dependentprocess•ribonucleoproteincomplexesratherthannakedRNAsmRNA的输出snRNA的输出核内蛋白质的输出3分子伴侣(chaperones)3.1分子伴侣的发现及种类◆Theterm“chaperonewasfirstusedbyRonLaskeyandhiscolleaguestodescribeaprotein(nucleoplasmin)thatisrequiredfortheassemblyofnucleosomesfromhistonesandDNA.◆Nucleoplasminbindstohistonesandmediatestheirassemblyintonucleosomes,butnucleoplasminitselfisnotincorporatedintothefinalnucleosomestructure.◆Chaperonesthusactascatalyststhatfacilitateassemblywithoutbeingpartoftheassembledcomplex.分子伴侣的概念及其特点◆1991年Ellis等人提出:●由不相关类的蛋白质组成的一个家系●它们介导其它蛋白质的正确装配●但自己不成为最后功能结构中的组分。◆该概念有以下特点:●凡具有“介导”功能的蛋白,都称为分子伴侣,可以是完全不同的蛋白质;●作用机理尚不清楚,故用“介导”二字,伸缩性较大；●分子伴侣一定不是最终结构的组成部分,但不一定是一个分离的实体;●装配的涵意比较广,包括:帮助新生肽的折叠,越膜定位,亚基组装等。◆Itisimportanttonotethat:●Chaperonesdonotconveyadditionalinformationrequiredforthefoldingofpolypeptidesintotheircorrectthree-dimensionalconformations.●Thefoldedconformationofaproteinisdeterminedsolelybyitsaminoacidsequence.●Rather,chaperonescatalyzeproteinfoldingbyassistingtheself-assemblyprocess.●Theyappeartofunctionbybindingtoandstabilizingunfoldedorpartiallyfoldedpolypeptidesthatareintermediatesalongthepathwayleadingtothefinalcorrectlyfoldedstate.分子伴侣的基本功能◆分子内伴侣(intromolecularchaperones)◆分子伴侣的分布●从细菌到人,从动物到植物●细胞质、线粒体、叶绿体和微体分子伴侣结构上的共同特点◆家族成员具有高度保守性◆家族成员结构上具有相似性◆大部分在体内为组成型表达,在刺激条件下会被进一步诱导。Hsp60的电镜三维镜象照片3.2functionsofchaperones◆帮助蛋白质折叠和装配◆蛋白质的转运和定位◆参与细胞器和细胞核结构的发生◆应激反应◆参与信号转导ActionofchaperonesduringtranslationActionsofchaperonesGroEL,GroESofE.coliinproteinfoldingSequentialactionsofHsp70andHsp60chaperonesActionofchaperonesinsignalingActionofchaperonesduringproteintransportMolecularChaperones◆应激反应●Molecularchaperoneswereinitiallyidentifiedasheat-shockproteins,agroupofproteinsexpressedincellsthathavebeensubjectedtoelevatedtemperaturesorotherformsofenvironmentalstress.●Theheat-shockproteins(abbreviatedHsp),whicharehighlyconservedinbothprokaryoticandeukaryoticcells,arethoughttostabilizeandfacilitatetherefoldingofproteinsthathavebeenpartiallydenaturedasaresultofexposuretoelevatedtemperature.●However,manymembersoftheheat-shockpr