分子生物学10-22--核小体

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1、染色体与DNAFigureCO:Xchromosomeinblue染色体2.1.1染色体概述染色体(chromosome)是细胞核中载有遗传信息的物质，在显微镜下呈丝状或棒状，由核酸和蛋白质组成，在细胞发生有丝分裂时期容易被碱性染料着色，因此而得名。同一物种内每条染色体所带DNA的量是一定的，但不同染色体或不同种中间变化很大。原核细胞染色体外裹着稀疏的蛋白质，其中一部分与DNA的折叠有关，另一些则参与DNA复制、重组及转录过程。真核细胞的染色体中，DNA与蛋白质完全融合在一起，其蛋白质与相应DNA的质量比约为1:1.chromosome–Adiscreteunitof

2、thegenomecarryingmanygenes.EachconsistsofaverylongmoleculeofduplexDNAandanapproximatelyequalmassofproteins.Itisvisibleasamorphologicalentityonlyduringcelldivision.Athinsectionshowsthebacterialnucleoidasacompactmassinthecenterofthecell原核细胞染色体(类核Nucleoid)ThenucleoidspillsoutofalysedE.coli

3、cellintheformofloopsofafiberThebacterialgenomeconsistsofalargenumberofloopsofduplexDNAFIGURE08:AnunrestrainedsupercoilintheDNApathcreatestension,butnotensionistransmittedalongDNAwhenasupercoilisrestrainedbyproteinbindingThesisterchromatidsofamitoticpaireachconsistofafiber(~30nmindiamete

4、r)compactlyfoldedintothechromosome真核细胞染色体类核；染色质；包装比例nucleoid–Thestructureinaprokaryoticcellthatcontainsthegenome.TheDNAisboundtoproteinsandisnotenclosedbyamembrane.chromatin–ThestateofnuclearDNAanditsassociatedproteinsduringtheinterphase(betweenmitoses)oftheeukaryoticcellcycle.packingra

5、tio–TheratioofthelengthofDNAtotheunitlengthofthefibercontainingit.SpecificSequencesAttachDNAtoanInterphaseMatrix（分裂间期基质）DNAisattachedtothenuclearmatrixatspecificsequencescalledMARsorSARs.TheMARsareA-T-richbutdonothaveanyspecificconsensussequence.chromosomescaffold（支架）–Aproteinaceousstru

6、ctureintheshapeofasisterchromatidpair,generatedwhenchromosomesaredepletedofhistones.ChromatinIsDividedintoEuchromatinandHeterochromatinRegionsofheterochromatinremaindenselypackedthroughoutinterphase.chromocenter–Anaggregateofheterochromatinfromdifferentchromosomes.Regionsofcompacthetero

7、chromatinareclusterednearthenucleolusandnuclearmembrane常染色质和异染色质EuchromatinandHeterochromatinDNAIsOrganizedinArraysofNucleosomes（核小体）ThecoreDNAisthelengthof146bpthatisfoundonthecoreparticlesproducedbyprolongeddigestionwithMNase.LinkerDNAistheregionof8to114bpthatissusceptibletoe