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1、Chapter9DNAandChromosomeEukaryotesPackageDNAinChromatinandChromosomePackedinsidethenucleusofeveryhumancellisnearly2mofDNA,whichissubdividedinto46individualmolecules,oneforeachchromosome.Collectingallthismaterialintoamicroscopicnucleusisanextraordinaryfe
2、atofpackaging.Duringinterphase,DNAiscombinedwithproteinsandorganizedintoaprecise,compactstructure,adensestring-likefibercalledchromatin,whichcondensesfurtherintochromosomesduringcelldivision.ConceptsofchromatinandchromosomeChromatin:fiber-likecomplexofD
3、NA,histones,andnonhistoneproteinsduringeukaryoticinterphase.Chromosome:DNAmoleculeistightlypackagedintothread-likestructurethatappearatMphase.Theirchemicalcompositionsareidentical.CondensationofchromatinduringMphaseyieldsthevisiblemetaphasechromosomes.C
4、omponentsofchromatin¾DNA¾Histones¾Nonhistones¾RNAComponentofchromatin---DNADNAisadoublehelixformedbybasepairsattachedtoasugar-phosphatebackbone.Anaveragehumancellcontainsabout6.4billionbasepairs,constitutingaDNAmoleculefully2mlong.ThreeDNAconformationsA
5、-DNAB-DNAZ-DNAThecomplexityofeukaryoticgenomes∑Genome:Onecopyofallthegeneticinformationofanorganism.∑Genomesizegenerallyincreaseswithanorganism’scomplexity.Ifeachnucleotidepairis1mm,thenthehumangenomewouldextend3200km,farenoughtostretchacrossthecenterof
6、Africa,thesiteofourhumanorigins.TandemlyrepeatedDNA:Simple-sequence,Highlyrepeated,NoncodingSatelliteDNA:Centromeres,Telomeres(105~107bp)MicrosatelliteDNA:102~105bpateachsiteMinisatelliteDNA:10~100bpateachsiteInterspersedmoderatelyrepeatedDNAIntersperse
7、drepeatedDNAmakesup25-40%ofmostmammaliangenomes.Alufamily:~300bplong/unit,accountingforabout10%ofthehumanDNAThreekeyregionsofchromatinReplicationoriginsequence:contributiontooriginactivityofDNAreplicationCentromeresequence:contributiontopropersegregatio
8、nofchromosomesTelomeresequence:protectionchromosomalextremfromnucleasesattackDNApackagingNucleosomesarethebasicunitofchromatinstructureEachhumancellcontainsabout2mofDNAwithinnucleusifstretchedend-to-end,yetthenucleusofahumancelli
