DNA是遗传物质

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1、Chapter1GenesareDNADNA是遗传物质DNA为双螺旋DNA的复制是半保留的通过碱基配对进行核酸杂交突变改变了DNA的序列突变集中于热点顺反子是单个DNA片断多重等位基因的种类DNA的物理交换导致重组遗传密码是三联体细菌的基因和蛋白是共线性的顺式作用点和反式作用分子遗传信息可由DNA或者RNA提供本章主要内容Figure1.1Abriefhistoryofgenetics.1.1IntroductionGenesareDNAAvirulentmutantsofavirushavelostthecapacitytoinfectahostcellproductively

2、,thatis,tomakemorevirus.TransfectionofeukaryoticcellsistheacquisitionofnewgeneticmarkersbyincorporationofaddedDNA.TransformingprincipleisDNAthatistakenupbyabacteriumandwhoseexpressionthenchangesthepropertiesoftherecipientcell.1.2DNAisthegeneticmaterialFigure1.2ThetransformingprincipleisDNA.1.

3、2DNAisthegeneticmaterialFigure1.3ThegeneticmaterialofphageT2isDNA.1.2DNAisthegeneticmaterialFigure1.4EukaryoticcellscanacquireanewphenotypeastheresultoftransfectionbyaddedDNA.1.2DNAisthegeneticmaterialAntiparallelstrandsofthedoublehelixareorganizedinoppositeorientation,sothatthe5′endofonestra

4、ndisalignedwiththe3′endoftheotherstrand.Basepairingdescribesthespecific(complementary)interactionsofadeninewiththymineorofcytosinewiththymineinaDNAdoublehelix(theformerisreplacedbyadeninewithuracilindoublehelicalRNA).Complementarybasepairsaredefinedbythepairingreactionsindoublehelicalnucleica

5、cids(AwithTinDNAorwithUinRNA,andCwithG).SupercoilingdescribesthecoilingofaclosedduplexDNAinspacesothatitcrossesoveritsownaxis.1.3DNAisadoublehelixFigure1.5Apolynucleotidechainconsistsofaseriesof5￠-3￠sugar-phosphatelinksthatformabackbonefromwhichthebasesprotrude1.3DNAisadoublehelixFigure1.6Th

6、edoublehelixmaintainsaconstantwidthbecausepurinesalwaysfacepyrimidinesinthecomplementaryA-TandG-Cbasepairs.ThesequenceinthefigureisT-A,C-G,A-T,G-C.1.3DNAisadoublehelixFigure1.7Flatbasepairslieperpendiculartothesugar-phosphatebackbone.1.3DNAisadoublehelixFigure1.8ThetwostrandsofDNAformadoubleh

7、elix.1.3DNAisadoublehelixDNApolymerasesareenzymesthatsynthesizeadaughterstrand(s)ofDNA(underdirectionfromaDNAtemplate).Maybeinvolvedinrepairorreplication.DNAasesareenzymesthatattackbondsinDNA.Endonucleasescleavebondswithinanucleicacidchain;th