分子试题07

1课程编号:06000014北京理工大学2009-2010学年第2学期2007级分子生物学期末试题A卷班级学号姓名成绩Part1.BasicConcepts(20points,2pointseach)1.PromoterRNA聚合酶同启动子结合的区域称为启动子区。将各种原核基因同RNA聚合酶全酶结合后，用DNaseI水解DNA，最后得到与RAN聚合酶结合而未被水解的DNA片段，这些片段有一个由5个核苷酸(TATAA)组成的共同序列，以其发现者的名字命名为Pribnow框(Pribnowbox)，这个框的中央位于起点上游10bp处，所以又称—10序列(—10sequence)，后来在—35bp处又找到另一个共同序列(TTGACA)。Hogness等在真核基因中又发现了类似Pribnow框的共同序列，即位于—25～—30bp处的TATAAAAG，也称TATA框(TATAbox)。TATA框上游的保守序列称为上游启动子元件(upstreampromoterelement，UPE)或上游激活序列(uptreamactivatingsequence，UAS)。另外在—70～—78bp处还有一段共同序列CCAAT，称为CAAT框(CAATbox)2.Z-DNAZ-DNA又称Z型DNA，是DNA双螺旋结构的一种形式，具有左旋型态的双股螺旋（与常见的B-DNA相反），并呈现锯齿形状。Z-DNA为三种具生物活性的DNA双螺旋结构之一。3.ToprimDomainThetoprim(topoisomerase-primase)domainisaconservedregionfromDnaGprimases,topoisomerases,OLDfamilynucleasesandRecR/MDNArepairproteins.ThefoldoftheTOPRIMdomainresemblesaRossman-likenucleotidebindingfold,withacentralbeta-sheetformedby4parallelbeta-strandsflankedby3alpha-helices.Only5residuesareconservedacrossallTOPRIMdomain,2oftheseareglycineswhichmayplayastructuralrole,theother3areacidicresiduesthatarepresentin2conservedsequencemotifs.ThesemayhaveametalbindingfunctionTheTOPRIMdomainmayformashallowgrooveonthesemoleculesandplayaroleinthebindingofdouble-helicalDNA/RNAhybrids.4.Pre-mRNAPrecursormRNA(pre-mRNA)isanimmaturesinglestrandofmessengerribonucleicacid(mRNA).pre-mRNAissynthesizedfromaDNAtemplateinthecellnucleusbytranscription.pre-mRNAcomprisesthebulkofheterogeneousnuclearRNA(hnRNA).ThetermhnRNAisoftenusedasasynonymforpre-mRNA,althoughstrictlyspeakinghnRNAmayincludenuclearRNAtranscriptsthatdonotendupascytoplasmicmRNA.Oncepre-mRNAhasbeencompletelyprocessed,itistermedmaturemessengerRNA,maturemRNA,orsimplymRNA.5.V(D)JRearrangementsV(D)JRearrangements/recombination,alsoknownassomaticrecombination,isamechanismofgeneticrecombinationintheearlystagesofimmunoglobulin(Ig)andTcellreceptors(TCR)productionoftheimmunesystem.V(D)Jrecombinationnearly-randomlycombinesVariable,Diverse,andJoininggenesegmentsofvertebrates,andbecauseofitsrandomnessinchoosingdifferentgenes,isabletodiverselyencodeproteinstomatchantigensfrombacteria,viruses,parasites,dysfunctionalcellssuchastumorcells,2andpollens6.SlippageDNAReplicationSlippageDNAReplicationinvolvesdenaturationanddisplacementoftheDNAstrands,resultinginmispairingofthecomplementarybases.SlippedstrandmispairingisoneexplanationfortheoriginandevolutionofSatelliteDNA.SlippedStrandMispairinghasalsobeenshowntofunctionasaPhasevariationmechanismincertainbacteria.7.CpGIslandDNAthathaveahigherconcentrationofCpGsites,knownasCpGislands.ManygenesinmammaliangenomeshaveCpGislandsassociatedwiththestartofthegene.Becauseofthis,thepresenceofaCpGislandisusedtohelpinthepredictionandannotationofgenes.TheseincreasedconcentrationsofCpGsmightbeassociatedwiththedecreasedmethylationofcytosinesoftenobservedinCpGislands—thiscouldresultinareducedvulnerabilitytotransitionmutationsand,asaconsequence,ahigherequilibriumdensityofCpGssurviving.8.SensestrandSensestrandiscomplementarytotheantisensestrandornonsensestrand.TheantisensestrandisthestrandofDNAtranscribedintomRNAduringtranscription.Theimmediateproductofthistranscriptioniscalledan(initial)RNAtranscript,whichisthesameasthesensestrandexceptthenucleotidesareRNAinsteadofDNA,andthebaseuracilissubstitutedforthymine.9.GeneralTranscriptionfactor(GTF)Generaltranscriptionfactors(GTF's)orbasaltranscriptionfactorsareproteintranscriptionfactorsthathavebeenshowntobeimportantinthetranscriptionofclassIIgenestomRNAtemplates.Manyofthemareinvolvedintheformationofapreinitiationcomplex,which,togetherwithRNApolymeraseII,bindtoandreadthesingle-strandedDNAgenetemplate.10.EpigeneticsEpigeneticsisthestudyofinheritedchangesinphenotype(appearance)orgeneexpressioncausedbymechanismsotherthanchangesintheunderlyingDNAsequence,hencethenameepi-(Greek:επί-over,above)-genetics.Thesechangesmayremainthroughcelldivisionsfortheremainderofthecell'slifeandmayalsolastformultiplegenerations.Part2.MultipleOptions(20points,2pointseach)1.WhichofthefollowingreagentsorconditionswouldnotbeexpectedtodestabilizeaDNAdoublehelix?Key:(3)(1)Heat;(2)Nucleases;(3)Organiccations,suchastheaminoacidlysine(4)Reagentsthatcanformhydrogenbonds,suchasurea,lowionicstrength2.TheeukaryoticfactorTFIIDisanalogousinfunctiontoprokaryotic:Key:(2)（1）NusA（2）Sigma（3）Rho（4）ThebetasubunitofRNApolymerase3（5）ThealphasubunitofRNApolymerase3.Whichofthefollowingtypesofenzymesmaynotbeinvolvedinexcision-repair?Key:(2)(1)DNApolymerase;(2)RNApolymerase;(3)DNAligase;(4)helicase;(5)exonuclease4.Double-strandednucleicacidhelices:Key:(4)（1）donothaveahandedness.（2）arealwaysright-handed.（3）arealwaysleft-handed.（4）canbeeitherright-orleft-handed.5．NucleotidescontainingasufurinplaceofoneoftheoxygensonthealphaphosphateareincorporatedintoDNA.Whenthefidelityofreplicationisstudiedusingthesenucleotides,anincreaseintheerrorrateofabout100-foldisobserved.Thisisbecause:Key:(3)(1)Thesubstitutionaffectsbase-pairing,leadingtohighermismatchformation.(2)Thesubstitutionaffectsnicktranslation,inhibiting5'--3'exonucleaseactivity.(3)Thesubstitutionaffect