21世纪是生命科学的世纪20世纪后叶分子生物学的突破性

PAGEPAGE54—简答题

第一章 绪论2120主要领域？答案：同；生物大分子单体的排列（核苷酸，氨基酸）导致了生物的特异性。三大支撑学科：细胞学，遗传学和生物化学。研究的三大主要领域：主要研究生物大分子结构与功能的相互关系，其中包括DNA之间的相互作用；激素和受体之间的相互作用；酶和底物之间的相互作用。答案：有人把它定义得很广：从分子的形式来研究生物现象的学科。但是这个定义使分子生物学难以从分子角度来解释基因的结构和活性是本书的主要内容。3二十一世纪生物学的新热点及领域是什么？答案：结构生物学是当前分子生物学中的一个重要前沿学科，它是在分子层次上从结构角度特别是从理学、化学和计算数学等多学科交叉的，以结构（特别是三维结构）和异常病理现象的关系。分子发育生物学也是当前分子生物学中的一个重要前沿学科。人类基因组计划，被称21 世纪生命科学的敲门‖“人类基因组计划”以及“后基因组计划”的全面展开将进入从分子水平阐明生命活动本质的辉煌时代。目前正迅速发展的生物信息学，被称为“21世纪生命科学迅速发展的推动力。尤应指出，建立在生物信息基础上的生物工程制药产业在21世纪将逐步成为最为重要的新兴产业从单基因病和多基因病研究现状可以看出这两种疾病的诊断和治疗在21世纪将取得不同程度的重大进展遗传信息的进化将成为分子生物学的中心内‖的观点认为，随着人类基因组和许多模式生物基因组序列的测定通过比较研究，人类将在基因组上读到生物进化的历史，使人类对生物进化的认识从表面深入到本质；研究发育生物学的时机已经成熟。在21世纪，遗传信息的进化研究成果，将成为解决发育问题的基础，发育问题这一难题可望获得突破性进展；21世纪，生物技术产业化的趋势将不断加剧基因工程技术转基因技术和基因治疗技术等将对21世纪的产业结构产生深远的影响。当前，生命科学基础研究中最活跃的前沿主要包括：分子生物学、细胞生物学、神经生物学、生态学，并由这些活跃的前沿引伸出诸如：基因组学、蛋白质组学、人类基因组计划、后人类基因组计划、克隆羊、克隆鱼、脑的十年、生物的多样性等时髦的名词和热门话题。相应的应用研究或技术研究也正趋成熟并逐渐普及，如生物工程，即基因工程、蛋白质工程、发酵工程、酶工程、细胞工程、胚胎工程等。由于生命科学与人类生存、人们健康、社会发展密切相关，必将成为21世纪全球关注的领域。4.简述分子生物学的发展历程。答案：从1847——识，而Morgan化学研究的进展，Watson和Crick又提出了脱氧核糖核酸的双螺旋模型，为充分揭示遗传信息的传递规律铺平了道路。在蛋白质化学方面，继Sumner1936利用纸1953Kendrew和Perutz利用X子氧过程中的特殊作用，成为研究生物大分子空间立体构型的先驱。20世纪401941年，曾在摩尔根实验室工作过的美国遗传的新概念（后来有所修改，40年代中期被普遍承认，从而建立了生物化学、遗传学。M.德尔布吕克和其同事们在1946年，美国微生物学家J.莱德伯格同E.L.现象。这两项突破以及他们对噬菌体和大肠杆菌的一些基本研究，对分子生物学的发展起了十分重要的作用。1944DNA证明DNADNA们对DNA化学组成和晶体结构的研究。1953425J.D.沃森和英国的──DNA双螺旋结构的分子模型。这一成就后来被誉为20最伟大的发现，也被认为是分子生物学诞生的标志。50年代在蛋白质的结构分析方面也取得了重要成果。英国生物化学家F.桑格第一次分析出含有51个氨基酸的胰岛素的氨基酸顺序。这一成果对准确地研究蛋白质本身结构和功能之间的关系，以1973300多种蛋白质的氨基酸1977DNA碱基顺序的分析方法并完成了分析φχ174噬菌体DNA的全部约5400的布口刺格父子及他们的学生创立并发展的X佩鲁茨自30年代末开始，就系统地研究了血红蛋白的结构。1969年完成了全部641961年法国细胞遗传学家雅各布和J.美国分子生物学家H.M.特明和D.巴尔的摩长期从事肿瘤病毒研究的基础上，于1970年分别独立地发现鸡肉瘤病毒和白血病病毒都是RNA病毒。在此基础上他们发现了依赖于RNADNA聚合酶即反转录酶。反转录酶能使RNA链上的遗传密码反转录给DNA。这一发现不仅对某些肿瘤的病因作了分子生物学的阐明，而且动摇了中心法则的不可逆性，成为中心法则的重要补充。真核细胞内的调控机制要复杂得多，也是当前生物学家重点探索的问题之一。在此基础之上，分子生物学发展的速度越来越快。一选择题

第二章 基因的概念ADNAnucleotidemayconsistof DNA核苷酸可能有下列哪一项组成A›aribosesugar,aphosphategroup,andadenine.B›aphosphategroup,deoxyribose,andcytosine.C›uracil,deoxyribose,andaphosphategroup.D›deoxyribose,thymine,andahydroxylgroup.Whichisthemostaccuraterepresentationoftheorganizationlevelsofthegeneticinformationincells? 下列哪一项最准确地代表了细胞中遗传信息的组织水平A›genesnucleotidechromosomesgenome.B›genomegenesnucleotideschromosomes.C›chromosomesgenesnucleotidesgenome.D›nucleotidesgeneschromosomesgenome.EukaryoticcellsdifferfromprokaryoticcellsinthatonlytheformercontainA›ribosomes.B›cytoplasm.C›DNA.D›anucleus.TheprokaryoticorganismthathasbeenthesubjectofmanygeneticstudiesisA›Saccharomycescerevisiae.B›Neurosporacrassa.C›E.coli.D›Drosophilamelanogaster.WhichelementisnotfoundinamoleculeofDNA?DNA分子中发现？A›carbon.B›sulfur.C›nitrogen.D›oxygen.WhichisfoundinRNA,butnotDNA?RNADNA分子中出现？A›Phosphate.B›Adenine.C›Ribose.D›Cytosine. ThetwopolynucleotidechainsinamoleculeofDNAareheldtogetherby whattype of DNA分子中的两条多核苷酸链是依赖于哪一种类型的化学键结合在一起的？A›Phosphodiester.B›Phosphate.C›Peptide.D›hydrogen.TheDNAthatmakesupbacterialchromosomesA›single-stranded.B›circularandsupercoiled.C›complexedwithhistones.D›alltheabove.WhichofthefollowingisaDNAbasepair?A›A-T.B›T-C.C›A-U.D›G-T.WhichofthefollowingisaRNAbasepair?A›A-T.B›A-C.C›U-C.D›U-A.TheDNAandhistoneproteinsinaeukaryoticchromosomearecompactedintostructurescalled 和组蛋白组成的结构称为A›proteosomes.蛋白体B›nucleosomes.C›telomeres.端粒D›centromeres.着丝粒Inhistransformationexperiments,FrederickGriffithobservedthatvirulentstrainsofStreptococcuspneumoniaeproducedcolonies.菌落A›smooth,shinyB›rough,dryC›exceptionallylargeD›unusuallycoloredViralgenomesmaybecomposedof病毒基因组的可能组成是A›RNAB›DNAC›eitherRNAorD›bothRNAandDNA.IntheHershey-Chaseblenderexperiments,theirmajorconclusionwasthatHershey 和Chase合实验得出的主要结论是A›asinglegenedirectedthesynthesisofasinglepolypeptide.B›DNAwasthegeneticmaterial.C›DNAwasadoublehelix.D›thegeneticmaterialwaslocatedinthenucleusofcells.ThetypeofDNAfoundmostcommonlyinlivingcellsisthe form.DNA构型是A›A.B›B.C›D›ZGeneslocatedinwhichregionofaeukaryoticchromosomearemostlikelytobetranscribed? 基因于真核生物染色区域时最有可能被转录A›centromere着丝粒.B›telomere端粒.C›euchromatin常染色质D›heterochromatin异染色质Anucleosideconsistsofa 核苷的基本组成是A›pentosesugarandanitrogenousbase.B›phosphategroupandanitrogenousC›pentosesugarandaphosphategroup.D›pentosesugar,aphosphategroup,andanitrogenousbaseProkaryoticchromosomesconsistmostlyofA›uniquesequenceDNAonly.B›repetitivesequenceDNAC›eitheruniquesequenceorrepetitivesequenceD›bothuniquesequenceandrepetitivesequenceTocreateakaryotype染色体, chromosomesarespreadonaslideandstained.A›interphase.B›telophase.C›metaphase.D›anaphase20AchromosomefromanunknownmicroscopicorganismisexaminedandfoundtocontainonlyuniquesequenceDNA.ThisorganismismostlikelyA›virus.B›bacterium.C›fungus.D›protozoan.Ineukaryoticcells,thegeneticmaterialisfoundintheA›ribosomes.B›nucleus.C›endoplasmicreticulum.D›cytoplasm.Griffith’sexperimentinjectingamixtureofdeadandlivebacteriaintomicedemonstratedthat(choosethecorrectanswer):明（选择正确的答案）A›DNAisdouble-strandedB›mRNAofeukaryotesdiffersfrommRNAofprokaryotesC›AfactorwascapableoftransformingonebacterialcelltypetoanotherD›BacteriacanrecoverfromheattreatmentiflivehelpercellsarepresentTheX-raydiffractiondataobtainedbyRosalindFranklinsuggested(choosethecorrect罗莎琳德•X射线衍射图像的数据表明（选择正确的答案）A›DNAisahelixwithapatternthatrepeatsevery3.4nanometersB›PurinesarehydrogenbondedtopyrimidinesC›DNAisaleft-handedhelixD›DNAisorganizedintonucleosomesGriffithinjectedmicewithdifferenttypesofbacteria.Foreachofthefollowingbacteriatypesinjected,indicatewhetherthemicelivedordied:的细菌类型，判断老鼠是存活还是死亡？a. typeⅡR b. typeⅢS c. heat-killedⅢS d. typeⅡR+heat-killedⅢSA›lived lived died diedB›died lived died C›lived died lived diedD›died died lived lived二填空题1．基因敲除Geneknock-ou）即是（将特定基因失活的过程，它是研究（基因功能）遗传学方法。2（pseudogen）因。3．在原核生物的基因表达调控中，因为没有核膜，（转录）和（翻译）是耦联的。4．Anucleosomeiscomprisedoftwocopiesofhistones（H2A），（H2B），（H3），（H4），onecopyofhistone（H1），and（200）bpofDNA.三简答题Fromachemical（bonding）view, whyisdouble-strandedDNAsostable?从化学（键）DNA比较稳定的原因答案：Hydrogenbondsbetweenbasesandhydrophobicbondsduetobasestacking碱基之间的氢键以及疏水的碱基堆积力。Whatis―Chargaff’sRule‖规则的内容是什么？答案：A%=T%andG%=C%indsDNA.腺嘌呤和胸腺嘧啶的摩尔数相等，即A=T；鸟嘌呤和胞嘧啶的摩尔数相等，即G=C；含氨基的碱基（A和C）总数等于含酮基的碱基（G和T）总数，即A+C=G+T；嘌呤的总数等于嘧啶的总数，即A+G=C+T。SupercoilingDNArequiresenergyandallowsworktobedone.Whataretwobiochemicalfunctionsthatthispent-upenergyisusedfor?DNA中的能量的主要用于哪两种生化作用？答案：Energycancausestrandseparationusedfor:（1）DNAreplication；（2）TranscriptionYouhaveisolatedaplasmidDNAthatisaclosedcircularmolecular1050bpinlengthwith5negativesupercoils. Whatarethelinkingnumber,helicalturns,writhe,andsuperhelicaldensity? 你分离出的质DNA1050bp5DNA螺旋数（缠绕数T）、扭曲数、以及超螺旋密度是多少？答案：Writhe=W=-5；helicalturns=T=1050/10.5=100；L=T+W=100+（-5）=95Superhelicaldensity=σ=W/T=-5/100=-0.05Whatisapseudogene,andhowdoyourecognizeone?什么是假基因？你如何识别出假基因？答案：Psuedogenesarearedefinedbytheirpossessionofsequencesthatarerelatedtothoseofthefunctionalgenes,butthatcannotbetranslatedintoafunctional假基因是指与正常基因结构相似，DNA序列，即不能翻译出有功能蛋白质的基因。canberecognizedbytheoccurrenceofoneormoremutationsthatobviouslyrenderthem可以利用补偿其功能的突变体而区分出假基因。Ineukaryoticcells,DNAispackagedintochromatin.Therepeatingunitofchromatiniscallednucleosome.被包装成染色质，其重复单元为核小体。Whatconstituteamononucleosome?每个核小体单元是由什么组成的？WhatistheconsequenceofDNApackagingontranscription?DNA怎样的影响后果？答案1Amononucleosomeiscomposedof146bpofcoreDNAwrappedaroundahistoneoctamerof2copiesofeachofH2A,H2B,H3andH4.146bp核心DNA和各两分子的组蛋H2AH2BH3、H4组成的八聚体构成。（2）TheconsequenceofDNApackagingistoinhibittranscriptionduetotheinabilityoftranscriptionmachineryandtranscriptionfactorstogainaccesstoDNA.DNA被包装成染色质结构后，会抑制转录。因为这一结构能够阻止转录机构及转录因子与DNA之间的相互接近。Whichcombinationsofhistonesform“histone-fold”dimerswitheachotherinthenucleosome?在核小体中，每个组蛋白二聚体分别由哪几种组蛋白组成？H3andH4formonedimerpair,H2AandH2Bformtheother.组蛋白H3和H4形成一个二聚体；组蛋白H2A和H2B形成另一个二聚体。ThroughX-raydiffractionanalysisofcrystallizedDNAoligomers,differentformsofDNAhavebeenidentified.TheseformsincludeA-DNA,B-DNA,andZ-DNA,andeachhasuniquemolecularattributes.DNAX-射线衍射分析，鉴定出了DNADNA不同的构型即A-DNA、B-DNA、Z-DNA，每一种构型各有其独特的分子特征。oftheseformsisthemostcommonforminlivingcells?在活的生物细胞中，普遍存在的分子构型是哪一种？（2）Z-DNAhasanunusualconformationresultinginmorebasepairsperhelicalturnthanB-DNA.Whatistheconformation?Doesthismoleculehaveanyfunctioninlivingcells?Z-DNA与B-DNA相比，每圈螺旋含有较多的碱基对数，请进一步说明Z-DNA具有怎样的功能？（3）Whichoftheseformsisneverfoundinlivingcells? 现。答案：（1）B-DNAistheformmostcommontolivingcells.B-DNA是活细胞中DNA的普遍存在形式。（2）Z-DNAisalongandthin(about2nmwide)doublehelix,likeB-DNA.Unliketheright-handedB-DNAhowever,Z-DNAisleft-handed.Ithasanaxisthatrunsthroughtheminorgroove,andhas12basepairsperhelicalturnthatareinclined8.8°fromaplaneperpendiculartotheaxis.Incontrast,B-DNAhasanaxisthatrunsthroughthebasepairs,andhas10basepairsperhelicalturnthatareinclined2° fromaplaneperpendiculartotheaxis.ThemajorgrooveofZ-DNAisnotverydistinct,asitisthinandflattenedoutalongthehelixsurface,whilethemajorgrooveofB-DNAiswideandintermediateindepth(betweenthatofA-DNAandZ-DNA).TheminorgrooveofZ-DNAisextremelynarrowandverydeep,whilethatofB-DNAisnarrowandofintermediatedepth. IthasbeenproposedthatregionswithZ-DNAprovideastretchofleft-handedhelicalturnsthatareinvolvedinreplication,recombinationandtranscription.Stretchesofleft-handedturnsmayaidinunwindingright-handedhelicalturnsinB-DNAduringtheseprocesses.Z-DNAmayalsobemorestableunderextremeenvironmentalconditions. 与B-DNA相比，Z-DNA比较A-DNAisfoundonlywhentheDNAisdehydrated,soitisunlikelythatlengthysectionsofA-DNAwouldbefoundinlivingcells.Benzer用一般遗传学方法测出T4rcistron中含有许多个突变子（或重组子）并且指出一个突变子的大小是1-3个核苷酸，后来证明这是科学上的一个惊人的预见。请回答：?你能说出在当时的条件下（没有DNA序列分析技术，遗传密码还没发现）1~3个核苷酸的结论。答案：基因是DNA基因内可以较低频率发生基因内的重组，交换。通过大量的成对突变型的杂交，测得其最小的重组频率为0.02%，即0.02个遗传图距。已知T415000.02少核苷酸：1.8×105÷1500×0.02=2.4bp因此指出一个突变子是1-3个核苷酸，暗示了三联体密码的存在。比较基因组的大小和基因组复杂性的不同：一个基因组有两个序列，一个是A，另一个是B2000bp长。其中一个是由400bp的序550bp40样？（2）这个基因组的复杂性如何？DNA（1）这个基因组的大小为4000bp；（2）这个基因组的复杂性为450bpWhatevidencedowehavethatinthehelicalformoftheDNAmoleculethebasepairsarecomposedofonepurineandonepyrimidine?我们有什么证据表明在DNA分子的螺旋构型中，在每一个碱基对中都含有一个嘌呤碱基和一个嘧啶碱基？答案：Twodifferentlinesofevidencesupporttheviewthatabasepairiscomposedofonepurineandonepyrimidine.有两方面的证据支持在DNAWhenthechemicalcomponentsofdouble-strandedDNAfromawidevarietyoforganismswereanalyzedquantitativelybyChargaff,itwasfoundthattheamountofpurinesequaledtheamountofpyrimidines.Morespecifically,itwasfoundthattheamountofadenineequaledtheamountofthymine,andthattheamountofcytosineequaledtheamountofguanine.Thesimplesthypothesistoexplaintheseobservationswastheexistenceofcomplementarybasepairing,AononestrandpairedwithTontheotherstrand,andGpairedwithC.MoredirectphysicalevidencewasprovidedbyX-raydiffractionstudies. TheseestablishedthedimensionsoftheDNAdoublehelixandallowedforcomparisonwiththeknownsizesofthebases. diameterofthedoublehelixisconstantthroughoutitslengthat2nm. Thisistherightsizeaccommodateapurinepairedwithapyrimidine,buttoosmallforapurine-purinepair,andtoolargeforapyrimidine-pyrimidinepair.Thedouble-helixmodelofDNA,assuggestedbyWatsonandCrick,wasbasedondatagatheredonDNAbyotherresearchers.Thefactsfellintothefollowingtwogeneralcategories;givetwoexamplesofeach:(1)chemicalcomposition;(2)physicalstructure. WatsonCrickDNA双螺旋模型，这些研究成果可以划分为两类即DNA的化学组成与DNA的物理结构。请详细阐述这两类研究成果的具体结论。答案：Thedouble-helixmodelofDNAsuggestedbyWatsonandCrickhadtoincorporateexistinginformationaboutitschemicalcompositionandphysicalstructure.Intermsofitschemicalcomposition,itwasknownthatDNAiscomposedofpolynucleotides,that(A)=(T)and(G)=(C)(Chargaff'srules),andthatwhilethepercentGCvariesbetweenorganisms,theA/TandG/Cratiosdonot.Intermsofitsphysicalstructure,thestructureandmoleculardimensionsofthecomponentmolecules(thebases,sugars,phosphates)wereknown. ItwasalsoknownfromstudiesofFranklinandWilkinsthatthemoleculeisorganizedinahighlyordered,helicalstructure,andthattherearetwodistinctiveregularitiesat0.34and3.4nmalongthemolecule'saxis.化学组成即DNA碱基组成的Chargaff规则：腺嘌呤和胸腺嘧啶的摩尔数相等，即A=T；鸟嘌呤和胞嘧啶的摩尔数相等，即G=C；含氨基的碱基C）总数等于含酮基的碱基T）总A+C=G+TA+G=C+TDNA异性。物理结构：DNA分子是由核苷酸组成，核苷酸有含氮的碱基、戊糖、磷酸构成。根据富兰克林和威尔金斯的x射线衍射图像表明：DNA分子是一个十分有序的双螺旋结构，每两个相邻碱基平面的垂直距离是3.4Å，每个螺旋包含10个碱基对。Hershey-Chase32P只标记在DNA35S只标记在35S35S标记的32P标记的噬菌体重复实验，那么在子代病毒中是否可以找到带32P标记的病毒？答案：因为DNA32P只标记在DNA35S只标记在蛋白质的外壳上。35S35S因此不带标记。32P35P35P标记的病毒。Theco-crystalstructureofORC（originrecognitioncomplex）boundtoDNAshowsthat200bpofDNAiswrappedin3fullright-handedturnsaroundtheyeastORCcomplex.YouassembleORContoacircular8kbplasmidcontaininganARS（autonomouslyreplicatingBeforeassembly,theplasmidhadanaverageof10negativesupercoils.Afterassembly,youextractthereactionwithphenol-chloroform,recovertheDNA,andrunitonagel.(Hint:DNAiswrappedinaleft-handedturnaroundnucleosomes).PleaseWhatisthelinkingnumber,twist,andwritheoftheplasmidafterextraction(assume10.5bp/turnofrelaxedBDNA).答案：W=-10（tennegativesupercoils）T=8000bp/10.5bpperturn=761or762L=T+W=751or752WheredoestheextractedDNAmigrateonanagarosegellackingethidiumbromide?答案：AtthepositionofsupercoiledDNA.Whatwillhappentothemobilityoftheplasmidasyouaddincreasingamountsofethidiumbromidetothegelduringelectrophoresis?Explainbriefly.SinceETBrlocallyuntwistsDNA(twistgoesdown),theplasmidwillacquirepositivesupercoils(writhegoesup).Atfirst,thiswillresultinthelossofnegativesupercoilsandtheplasmidwillmigratelessrapidly.IfyouaddenoughETBr,theplasmidwillbecomepositively supercoiledandmigrateatthepositionofsupercoiledDNA.Nowyourepeattheexperiment,butyouincludeTopoisomeraseIintheassemblyreaction.Undertheseconditions,whatisthelinkingnumber,twist,andwritheoftheplasmidafterextraction?答案：W=+3T=8000bp/10.5bpperturn=761orL=764or765The10negativesupercoilspresentintheplasmidwillbeinstantlyremovedbytopoisomeraseI,butthesolenoidalsupercoils,constrainedbyORC,willnot.AssumingthateachORCwillgenerate3positiveplectonemicsupercoils,afterproteinextraction,W=+3,T=761(sinceDNAalwaysadoptsthemostfavorablevalue),L=T+W=764.Inadditiontojuststatingthenameofthestrain,wewerelookingforatleastsomeexplanationofhowitwouldwork.选择题

第三章 DNA复制ThroughtheirexperimentswithDNAfromthebacteriumEscherichiac,eselsonandStahlshowedthatDNAreplicationDNA和StahlDNA复制是A›conservative.B›semi-conservative.C›DuplicativeD›dispersive.AttheconclusionofDNAreplication,thetworesultingDNAdoubleheliceseachDNA的复DNA双螺旋的两条链分别是A›oneparentalandoneprogenystrand.B›twoparentalortwoprogenystrands.C›stretchesofprogenyDNAinterspersedwithparentalDNAalongbothstrands.D›twonewlysynthesizedstrands.DNApolymerasesareenzymesthatcopyA›DNAintoB›DNAintoRNAC›RNAintoDNAD›RNAintoRNA.TobeginDNAreplication,ashort primermustfirstbeproduced.为了能够起始DNA的复制，一段短的 引物必须预先合成A›DNAB›RNAC›polypeptideD›histoneWhichE.coliDNApolymerasehastheabilityto―proofread‖newlysynthesizedDNAandremoveerroneousbases?在大肠杆菌中，哪一种DNA聚合酶对新合成的DNA具有校正功能，能把错配的碱基移去？A›DNApolymeraseIonlyB›DNApolymeraseIIIonlyC›DNApolymeraseIandIIID›allthreeDNApolymeraseshaveproofreadingabilityDuringsynthesis,allDNApolymerasesaddnucleotidesinwhichdirection?A›fromlefttorightB›from3’to5’C›from5’to3’D›inmorethanonedirectionatatimeIneukaryotes,DNAreplicationoccursduringwhichphaseofthecellcycle?A›B›G1C›G2D›MWhichofthefollowingisnotrequiredforDNAsynthesisreactions?A›dCTPsB›templateDNAC›DNApolymeraseD›calciumionsDNApolymerasecatalyzestheformationofaphosphodiesterbond betweenA›5’phosphateanda5’hydroxylgroup.B›3’phosphateanda5’hydroxylgroup.C›5’phosphateanda3’hydroxylgroup.D›3’phosphateanda3’hydroxylgroup.Thesequenceofnucleotides inonestrandofDNAis 5’-CCACTGG-3’,WhatisthesequenceofthecomplimentarystrandofA›5’-CCACTGB›3’-CCACTGC›5’-GGTCACC-3’D›3’-GGTGACInbacteriasuchasE.coli,replicationofthechromosomeisA›semidiscontinuousandbi-directional.B›discontinuousandunidirectional.C›continuousandbi-directional.D›semidiscontinuousandunidirectional.The3’5’exonucleaseactivityassociatedwithDNApolymerasereducesthefrequencyofreplicationerrorstoA›1/10.B›1/1,000.C›1/1,000,000.D›1/1,000,000,00.TheproofreadingactivityofDNApolymeraseremoveserrant nucleotidesfromthe ofastrand.A›3’endB›5’endC›3’and5’endD›middleOntheE.colichromosome,oriCA›encodesDNApolymeraseI.B›isabindingsiteforhistoneproteins.C›isthestartsiteforD›encodesanRNAprimer.TheenzymethatunwindsthedoublehelixtofacilitatereplicationisA›3’5’B›DNAhelicase.C›DNApolymerase.D›topoisomerase.WhentheDNAdoublehelixisreplicated,thenewlysynthesized5’ 3’strandisconsideredthe strand.A›B›laggingC›templateD›discontinuousSynthesisofthelaggingstrandA›continuously.B›conservatively.C›discontinuously.D›semidiscontinuously.WhichtypeofDNAisduplicatedbyrollingcirclereplication?A›bacteriophageλB›plasmidDNAC›bacteriophageΦX174D›alloftheaboveManytypesofmammaliancancercellsarenotablefortheirA›telomeraseactivity.B›lackoftelomeraseactivity.C›lackoftelomeres.D›increasednumberoftelomeres.TodeterminethenumberofreplicationsitesinE.coliandwhetherreplicationisunidirectionalorbidirectional,youexaminedtheresultsoftwodifferentexperiments.BothexperimentsinvolvedgrowingE.coliinamediumcontainingradioactivethymidine.Whatdidtheadditionofthymidinetothemediumallowyoutoobserveinbothexperiments? DNA什么？A›ThedifferencebetweentheleadingDNAstrandandthelaggingDNAstrand.B›ThedifferencebetweenthereplicatedandunreplicatedportionsofDNAC›ThedifferencebetweentheRNAprimerandthenewlysynthesizedDNA.ThedifferencebetweenthereplicationforkandthenewlysynthesizedDNA.D›Noneoftheabove.Basedontheexperimentsinthisactivity,whichofthefollowingistrueaboutE.colireplication?根据DNA复制的描述，下列那一项是正确的？A›Replicationbeginsatasinglesiteonthechromosome.B›Replicationisbidirectional.C›Synthesisbeginsatspecificsitesonthetemplatestrand.D›Alloftheabove.Duringreplication,proofreadingofthenewlysynthesizedDNAisperformedbyA›RNApolymeraseB›reversetranscriptaseC›topoisomeraseD›DNApolymerase尿嘧啶糖苷酶的功能是A›去除嘧啶二聚体B›切除RNA分子中的尿嘧啶C›切除DNAD›切除DNA分子中的尿苷酸E›切除RNA分子中的尿苷酸 DNADNA白质？A›DNA聚合酶Ⅰ、引发酶、SSB和连接酶B›SSB、解链酶、和拓扑异构酶C›连接酶、DNA聚合酶Ⅰ和ⅢD›DNASSBEDNA聚合酶ⅡDNA复制的几种酶的作用次序是A›DNA解链酶→引发酶→DNA聚合酶→DNA连接酶→切除引物的酶B›DNAC›引发酶→连接酶→切除引物的酶D›DNA聚合酶E›DNA连接酶→切除引物的酶将两段寡聚脱氧核苷酸片段和与DNA聚合酶一起加到含dGTPdCTPdTTPA2C∶1TB›1G∶1TC›3G∶2TD›E›5T∶4G∶3C∶1A噬菌体Φx174的基因组是一个由5386个碱基组成的单链DNA，该基因组编码有种不同的蛋白质，这些蛋白质约有2380能力。对这种现象最好的解释是A›它的基因组含有重叠基因B›氨基酸由二联体密码编码C›细胞核糖体翻译它的每一个密码子不止一个D›蛋白质在使用后即被后加工二填空题DNA复制的方向是从端到端展开。维持DNA复制的高度忠实性的机制主要有聚合酶的高度选择性（DNA校正功能）和（错配修复。端聚酶由和（蛋白质）两个部分组成，它的生理功能是（维持端粒的完整。染色体中参与复制的活性区呈Y型结构，称为（复制叉三简答题Explainthefollowingtermsandconcepts：请解释下列术语或概念：leadingstrandandlaggingstrand前导链和滞后链；Sigmafactorandholoenzymeσ因子与全酶。strandistheDNAstrandthatsynthesizedinthe5′to3′directionastheparentalduplexisunwound.ItisprimedonetimeduringsynthesisandusestheDNAstrand3’to5’astemplate.前导链是指随着亲本双螺旋的解开而按照5′3′方向连续合成的DNA子链，以方向的亲本链为模板。LaggingstandusestheDNAstrandthatruns5’to3’astemplateandsynthesisDNAnon-continuouslyasOkazakifragment.It'ssynthesisrequiresmultipleprimingevents.Aseriesofthesefragmentsaresynthesized,each5′–3′;thentheyarejoinedtogethertocreateanintactlaggingstrand.滞后链是指以5′3′方向的亲本链为模板，不连续合成一系列5′3′方向冈崎片断，然后连接成一条完整的子链DNA。滞后链的合成需要若干次引发事件的发生。SigmafactorandholoenzymeSigmafactorisacomponentofthebacterialRNApolymeraseholoenzymewhichiscomposedofRNAcoreenzymeandSigmafactor.Sigmafactorisresponsibleforpromoterrecognitionandtranscriptioninitiation,whileRNAcoreenzymeisresponsibleforRNAsynthesis.σisaSpecificityFactor，whichdirectsthecoretotranscribespecific因子是RNA聚合酶全σσRNA核心酶负责RNA的合成。是一种特异性因子，能够指导核心酶转录特异的基因。Whatisthetemplateusedbytelomerasetoaddtelomericrepeatsattheendsofchromosomes?端粒酶在向染色体末端添加寡聚重复单元时，以什么为模板？TelomerasecarriesitsownRNAtemplateforpolymerizationofthetelomereDNArepeats.Thatmeanstelomeraseisareversetranscriptase,i.e.anRNA-dependentDNApolymerase.端粒酶以自身携带RNADNARNADNA聚合酶。3．AspaceshiplandsontheEarthcarryingasampleofextraterrestrialbacteria.YouareassignedthetaskofdeterminingthemechanismofDNAreplicationinthisorganism.Yougrowthebacteriainunlabledmediumforseveralgenerations,thegrowitinpresenceof15Nforexactlyonegeneration.YouextracttheDNAandsubjectittoCsClcentrifugation.Thebandingpatternyoufindisasfollows:在利用飞船进行科DNA有标记的培养基上生长几代15N标记的培养基中准确地繁殖一代DNA并进行CsClItappearstoyouthatthisevidencethatDNAreplicatesinthesemiconservativemanner,butyouarewrno.rohy?Whatotherexperimentcouldyouperform(usingthe15N15N14N14N ExperimentalsamplesamesampleandtechniqueofCsClcentrifugation)thatwouldfurtherdistinguishbetweensemiconservativeanddispersivemodesofreplication?根据这一结果，你认为DNA行复制，但你的观点是不正确的，为什么？请你设计另一个实验方案（手段即CsCl梯度离心）能够有效地将半保留复制和弥散复制这两种复制方式区分开来。TheCsClcentrifugationresulteliminatesthepossibilityoftheconservativemodelofreplication,butisstillconsistentwitheithersemiconservativeordispersivemodelsofDNAreplication.TodistinguishbetweenthesetwopossibilitiesusingthesamesampleandthetechniqueofCsClcentrifugation,onecoulddenaturetheDNA,andthensubjectthesingle-strandedsampletoCsClcentrifugation.ThiscouldbedoneinpracticebyusinganalkalineCsClgradient,asthetwoDNAstrandswilldenatureathighpH.Theexpectedresultsareshownbelow.CsCl梯度离心的结果虽然排除了全保留复制的可能性，但不能根据这一结果就可证明DNA相同的技术手段即CsCl梯度离心将半保留复制和弥散复制区分开来的方法是将DNA样品变性，然后利用碱性CsCl梯度离心技术对单链DNA则出现一条带，如下图所示：

半保留复制变性后离心半保留复制变性后离心弥散复制变性后离心变性后离心弥散复制变性后离心KornbergisolatedDNApolymeraseⅠfromE.coli.DNApolymeraseⅠhasanessentialfunctioninDNAreplication.WhatarethefunctionsoftheenzymeinDNAreplication?科恩伯格从大肠杆菌中分离出了DNA聚合酶Ⅰ，在DNA聚合酶Ⅰ在DNA复制过程中具有什么功能？答案：DNApolymeraseⅠfunctionstoremovetheRNAprimersynthesizedduringtheinitiationofDNAreplicationandreplacethisRNAwithDNA.WhenDNApolymeraseⅢ,themainsyntheticenzymeforDNApolymerization,reachesanRNAprimer,itdissociatesfromtheDNA.DNApolymeraseⅠfunctionstocontinuesynthesisoftheDNAina5’-to-3’direction.ItsimultaneouslyremovestheRNAprimerusingits5’-to-3’exonucleaseactivity,andreplacestheRNAwithDNAnucleotides.DNA聚合酶ⅠDNARNA引物的功能，并合成一段DNARNADNA聚合功能的DNA聚合酶Ⅲ在遇到RNA引物时，就会从DNA5’，3’核酸外切酶的功能切除RNA5’3’方向合成DNA。DescribethemolecularactionoftheenzymeDNAligase.WhatpropertieswouldyouexpectanE.colicelltohaveifithadatemperature-sensitivemutationinthegeneforDNAligase?请描述DNA连接酶的DNA生怎样的表型效应？答案：DNAligasecatalyzestheformationofaphosphodiesterbondbetweenthe3’-OHandthe5’-monophosphate groups on either side of a single-strand DNA gap, sealing the gap.Temperature-sensitiveligasemutantswouldbeunabletosealsuchgapsattherestrictive(high)temperature,leadingtofragmentedlaggingstrands,andpresumablycelldeath.IfabiochemicalanalysiswereperformedonDNAsynthesizedafterE.coliwereshiftedtoarestrictivetemperature,therewouldbeanaccumulationofDNAfragmentsthesizeofOkazakifragments. ThiswouldprovideadditionalevidencethatDNAreplicationmustbediscontinuousononestrand.什么是DNA聚合酶的进行性？如何测定一种DNA聚合酶的进行性？答案：DNA聚合酶的进行性是指某一种DNA解离的这段时间内，催化了多少脱氧核苷酸的掺入。测定某一DNA特异性DNA，当DNA聚合酶从模板上解离下来后，由于大量的非特异性DNA稀释了原来的DNA模板，使得DNA聚合酶很难再与原来的模版结合，这样就得到了新合成的DNA泳可大概知道片段的长度。尽管DNA聚合酶催化聚合反应既需要模板，又需要引物。但下面的单链DNA却可以直接作为DNA聚合酶Ⅰ的有效的底物。试解释其中的原因，并写出由DNA结构。3’OH-TGGCTCATAGCCGGAGCCCTAACCGTAGACCACGAATAGCATTAGGp--’-5答案：由于此链DNA特殊的碱基组成，使得该DNA能够形成如图所示的茎环结构：T A OH3’G GAGCTAACCGTAGACCACGAATAGCATTAGG5’C C GDNA3’-OHDNA的外切酶活性将末端错配的T水解掉而引入正确的G，然后再进行延伸反应，最终得到的产物是： T A CTCGGATTGGCATCTGGTGCTTTCGTAATCC-OH’GC C G

GAGCCCTAACCGTAGACCACGAATAGCATTAGGp5’简述维持DNA复制的高度忠实性的机制。答案：维持DNA聚合酶所具有的3’5’RNADNA复制的忠实性，因为当DNARNA误。在冈崎提出DNADNA是仅仅是后随链才是不连续复制，存在着很大争议。显然前导链的合成不需要不连续复制，但是许多研究者发现经脉冲标记的冈崎片段可以和亲代DNADNA的两条链都可以作为冈崎片段的模板。试提出一种机制解释前导链的复制也可能产生冈崎片段，并设计一个实验证明你提出的机制。答案：前导链似乎也形成小的片断，是因为在一个细胞中，含有微量的dUTP，它在DNA复制过程中有可能代替dTTP掺入到新合成的子链中，由于脱氧尿苷酸不是DNA分子中的正常核苷酸，所以体内修复系统会将它除去。去除的机制是先在尿嘧啶糖苷酶的作用下切除DNA然后AP核酸内切酶在AP位点将DNAAP位点在内的一段DNA链切除，再由DNAAP核酸内切酶的作用必然导致前导链形成小的DNA片断。筛选AP核酸内切酶缺失的大肠杆菌突变株，观察上述现象是否发生。Telomeresareuniquerepeatedsequences.WhereontheDNAstrandaretheyfound?Dotheyserveafunction?端粒是一类特殊的重复序列。端粒序列存在于DNA链的什么部位？具有怎样的功能？答案：Telomeresarecharacteristicallyheterochromaticsequencesfoundattheendsofalinear,eukaryoticchromosome.Formostorganisms,thetelomericsequencesattheextremeendofachromosomearesimple,highlyrepeated,andspeciesspecific.Thesesequencesaresynthesizedbytheenzymetelomerase.Nearby,butnotattheveryendofachromosome,aretelomere-associatedsequences.Thesearerepeated,co