分子生物學(xué)教學(xué)課件：CHAPTER 7 Chromosomes,chromatin

Chapter7Chromosomes,chromatin,andthenucleosomeNucleus:細(xì)胞核;Nucleolus:核仁Nucleoid:類核Mitosis:有絲分裂；Meiosis：減數(shù)分裂interphase：分裂間期Histone:組蛋白；Nucleosome:核小體Chromosome:染色體；Chromatin:染色質(zhì)；eu-;hetero-Centromere(中心粒）Telomere（端粒）RepetitiveDNA(重復(fù)DNA)Tandemgenecluster（串聯(lián)基因簇）VocabularyCharacteristicsofEukaryoticGenome0.414.761021703060Length(cm)3.0×10910bp×3.4nm/helix=102cmTheimportanceofpackingofDNAintochromosomesChromosomeisacompactformoftheDNAthatreadilyfitsinsidethecellToprotectDNAfromdamageDNAinachromosomecanbetransmittedefficientlytobothdaughtercellsduringcelldivisionChromosomeconfersanoverallorganizationtoeachmoleculeofDNA,whichfacilitatesgeneexpressionaswellasrecombinationChromosomeThenucleosomeHigher-orderchromatinstructureRegulationofchromatinstructureNucleosomeassemblyDNAProteinChromosomes:DNAShape:circularorlinearNumberinanorganismischaracteristicCopy:haploid,diploid,polyploidproblemGenomesize:thelengthofDNAassociatedwithonehaploidcomplementofchromosomes

Genenumber:thenumberofgenesincludedinagenome

Genedensity:theaveragenumberofgenesperMbofgenomicDNAGenome&thecomplexityoftheorganism

Genome&thecomplexityoftheorganism

Genomesize/GeneDensity:1.Increasesingenesize:increaseinthesequenceofregulatorysequence;presenceofintrons(splicing)unique;repeated2.IncreasesintheDNAbetweengenes(intergenicsequences):

Pseudogenesareinactivebutstablecomponentsofthegenomederivedbymutationofanancestralactivegene.

PseudogenetheformationofpseudogeneFigure6.8theformationoftruncatedgene(截短基因)andgenefragment.tandemrepetitiveDNA

SatelliteDNA:

MinisatelliteDNAMicrosatelliteDNADispersedrepetitiveDNA產(chǎn)生原因——轉(zhuǎn)座：

遺傳元件在DNA中從一個位置移動到另一個位置的過程

RNA介導(dǎo)——真核存在/原核無機(jī)制：Retrotransposition

（反轉(zhuǎn)錄轉(zhuǎn)座）

反轉(zhuǎn)錄元件

DNA轉(zhuǎn)座子——原核常見/真核少

機(jī)制：復(fù)制型和保守型

水平基因轉(zhuǎn)移

3.TheRepetitiveDNAcontentofGenomes

(重復(fù)DNA序列)Figure6.15SatelliteDNAfromthehumangenomeSatelliteDNA(衛(wèi)星DNA):

核心序列為5－200bp，主要存在于染色體著絲粒區(qū)，Centrifugation(離心分離技術(shù))常用的兩類離心分離方法是差速離心(differentialcentrifugation)

密度梯度離心(densitygradientcentrifugation)離心分離細(xì)胞組分和生物分子是最常用的分離方法蔗糖密度梯度離心分離溶酶體、線粒體和微粒體CsCl密度梯度離心分離DNAFigure6.15SatelliteDNAfromthehumangenomeSatelliteDNA(衛(wèi)星DNA):

核心序列為5－200bp，主要存在于染色體著絲粒區(qū)，MinisatelliteDNA(小衛(wèi)星DNA)

核心序列為<25bp，主要存在于染色體靠近端粒處,與DNA復(fù)制有關(guān)

染色體其他位置的小衛(wèi)星DNA,功能不清

DNA復(fù)制時微衛(wèi)星拷貝有時發(fā)生滑移,導(dǎo)致插入或缺失一個或多個重復(fù)單位,使核心序列重復(fù)數(shù)目發(fā)生變化，以至于任何兩個不同個體間中都存在串聯(lián)數(shù)目的差異

-------可用于DNAFinger(DNA指紋)

可用來研究人群相關(guān)性

MicrosatelliteDNA(微衛(wèi)星DNA)指以2－7個堿基為核心單位串聯(lián)重復(fù)而成的一類序列，又稱為STRshorttandemrepeat(短串聯(lián)重復(fù)序列）MicrosatellitesareusefulforgeneticmappingOriginsofreplicationCentromeresTelomeresCriticalDNAelements

inChromosomeduplication&segregationFigure7-6Centromeres,originofreplicationandtelomerearerequiredforeukaryoticchrom.maintenanceMitoticchromosomeatmetaphaseKinetochore動粒Centromere著絲粒Centromere:著絲粒,aregionofchromosome(染色體)wheretwosisterchromatids(染色單體)arejoinedatmetaphase.2.Kinetochore:動粒,aproteincomplexattachingmicrotubules(微管)ofmitoticspindle(紡錘體)3.Telomere:

端粒,endofchromosomeMitoticspindleTelomere

端粒

Directtheformationofkinetochore(anelaborateproteincomplex)essentialforchromosomesegregationOnechromosome,onecentromereThesizevaries(200bp->40kb)ComposedoflargelyrepetitiveDNAsequencesCentromeresRequiredforthecorrectsegregationofthechromosomesafterreplicationChromosomeDNAProteinThemajorityoftheassociatedproteinsaresmall,basicproteinscalledhistones.

Otherproteinsassociatedwiththechromosomearereferredtoasnon-histoneproteins,includingnumerousDNAbindingproteinsthatregulatethetranscription,replication,repairandrecombinationofDNA.HalfofthemolecularmassofeukaryoticchromosomeisproteinChromosomeDNAProteinThenucleosomeDiscoveryComponentsAtomicstructureNucleosomes1973-1974:Nucleaseprotectionanalysis2.1974:electronmicrographs3.Biochemistryanalysis:Component:eighthistoneproteins

（H2A，H2B，H3，H4）

+140~150bpDNANucleaseproteinanalysisofchromatinfromhunmannuleiThenucleosomecomponentsDNAProteinscoreDNA:147bplinkerDNA:20-60bpHistonesFiveabundanthistonesStructuralfoldN-terminal“tail”Histonesaresmall,positivelycharged(basic)proteinsFigure7-19Thecorehistonesshareacommonstructuralfoldhistone-folddomainthesitesofextensivemodificationsH2BH2AH3H4a2a3a1a2a3a1a2a3a1a2a3a1L1L2aNH3H44helix-bundleH3H4H3’H4’4helix-bundleH4H2BH2AH4H2BH2AH3H4H2BH2AH3Diameter=110

AoH4H2BH2AH3Width=45AoChromosomeDNAProteinThenucleosomeDiscoveryComponentsAtomicstructureHydrogenbonds:histone(~140)DNA:phosphodiesterbackbone

7:Bases1.sequence-independentcontacts2.ThehistoneN-terminaltailsMinorgrooveThehistonetailsemergefromthecoreofthenucleosomeatspecificpositions,servingasthegroovesoftodirecttheDNAwrappingaroundthehistonecoreinaleft-handedmanner.ascrewChromosomeThenucleosomeDNAProteinHigher-orderchromatinstructureHistoneH1bindstothelinkerDNA30-nmfiber

FurthercompactionofDNAHistonevariantsHistoneH1bindstothelinkerDNAH1bindstwodistinctregionsofDNA

oneendofthenucleosomecentralDNAhelixofthenucleosomeTheadditionofHistoneH1leadtomorecompactnucleosomalDNAthe30-nmfiber6nuleosomes/superhelixLinkerDNAcirclesaroundthecentralaxisLinkerDNApassthroughthecentralaxisFurthercompactionofDNAinvolveslargeloopsofnucleosomalDNAAdditional103-104-foldcompactionisrequired,butthemechanismisunclearThenuclearscaffoldmodelisproposedThehigher-orderstructureofchromotinHistonevariantsSeveralhistonevariantsarefoundineukaryotesThisvariantscanreplaceoneofthe4standardhistonestoformalternatenucleosomesH2A.ZCENP-AisassociatedwiththenucleosomescontainingcentromericDNAFigures7-33AlterationofchromatinbyincorporationofhistonevariantsH3ChromosomeThenucleosomeHigher-orderchromatinstructureRegulationofchromatinstructureNucleosomepositioningModificationoftheN-terminaltailsofthehistonesDNAMustBeAccessedTheinteractionofDNAwiththehistoneoctamerisdynamic

NucleosomeremodelingcomplexesAlargeproteincomplexesfacilitatechangesinnucleosomelocationorinteractionwiththeDNAusingtheenergyofATPhydrolysis.Fig7-35NucleosomemovementcatalyzedbynucleosomeremodelingcomplexesremodlingISWIRemodelersSlideNucleosomeswithCoordinatedMulti-base-pairEntryStepsandSingle-base-pairExitStepsCELL,31JANUARY2013|Figure1:ThehistonechaperonecomplexFACTrecognizesthehistoneH2A-H2BheterodimerthroughtheSpt16MdomainofSpt16.StructuralbasisofhistoneH2A–H2BrecognitionbytheessentialchaperoneFACTNature,499,111–114(04Ju