chromatin structure

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1、Chapter9MolecularStructureofGenesandChromosomesEdition4:Chapter9,section9.5,pages320-332Edition5:Chapter10,section10.4,pages424-4371.3ProkaryoticcellsSinglecellorganismsTwomaintypes:bacteriaandarchaeaRelativelysimplestructureFigure1-7a1.3EukaryoticcellsSinglecellormul

2、ticellularorganismsPlantsandanimalsStructurallymorecomplex:organelles,cytoskeletonFigure1-7b8.3GeneticandphysicalmapsoftheE.colicircularchromosomeFigure8-14Length:About4000kbNeedtopackageDNAandmakeitcompacttofitinthecellE.coliDNAisabout1mmlong.E.colicellis1mmlongand0.

3、5-1.0mmwide.RandomcoiloftheDNAwillbe~1000timesbiggerthanthespaceavailable.Negativechargesduetophosphatesrepeleachotherandthemoleculestaysinextendedform.Chargeneutralizationwillhelptocompactit.VisualizationofthecircularE.colichromosomeCompact,foldedE.colichromosome9.5O

4、rganizingcellularDNAintochromosomesMostbacterialchromosomesarecircularwithonereplicationoriginEukaryoticchromosomeseachcontainonelinearDNAmoleculeandmultipleoriginsofreplicationBacterialDNAisassociatedwithpolyaminessuchasspermineandspermidineBacterialDNAisassociatedwi

5、thbasicproteinssuchasH-NSEukaryoticDNAassociateswithhistonestoformchromatinHumanGenome:3.3X109haploidsomeofthelongestchoromosomesarealmost8-10cmlong:2-3X108bpTotalhumanDNA(diploid)=about2.2meters,tobeputinaspherewithdiameterof10µmabout1to105compactionratio!Similartofi

6、ttingDNAthatwas2kilometersinlengthintoacellthatwas1cmindiameter!DNAlengthCalculation10bp=3.4nmLongesthumanchromosome(1)2.47X108bp2.47X108bp=3.4X2.47X107nm8.4X107nm8.4X104µm8.4X101mm8.4cm!Totaldiploidhumangenomeis6.6X109bp=2.2metersoflinearDNA!9.5Chromatinexistsinexten

7、dedandcondensedformsFigure9-29Lowsalt0.15M,physiologicalsalt9.5NucleosomesarecomplexesofhistonesFigure9-309.5ThesolenoidmodelofcondensedchromatinFigure9-31DimersofH2A,H2B,H3,andH4146bpwrappedpernucleosome15-50bpinthelinkerregionlittlelessthan2completeturnspernucleosom

8、e6nucleosomes/turninthesolenoidstructure9.6NonhistoneproteinsprovideastructuralscaffoldforlongchromatinloopsFigure9-34DNArel