2009年分子生物學(xué)quiz1參考答案(精)

2009年分子生物學(xué)quizl參考答案Whatiscentraldogma?Whatcontentshaveyoulearnedineachpartofthecentraldogma?(5’)Thecentraldogmaisthepathwayfortheflowofgeneticinformation.間是雙鍵，CGH一間是雙鍵，CGH一r鍵；AG是二環(huán)，TC是單環(huán)；氫鍵的位ThefeaturesofDNAstructure：Wehavelearntthemaintenanceofthegenome(thestructureofthegeneticmaterialanditsfaithfulduplication)andtheexpressionofthegenome(theconversionofgeneticinstructionscontainedinDNAintoproteins).(缺reversetranscription扣一分)Writeoutthestructureoffourbases,labelthepositionsthatparticipateWatson-Crickbasepairingandthatconnecttotheribose?(10’)如果解答中可以置等，會(huì)酌情wg/ qsugarWhatarethefeaturesofDNAstructure?AndhowRNAstructurediffersfromDNA?(2Copyright?2004PearsonEducationfInc.,publishingasBenjaminCummingsTwoantiparallelpolynucleotidechainsaretwistingaroundeachotherintheformofadoublehelix.6’(polynucleotide(buildingblock)2’,antiparallel2’,doublehelix2’)HydrogenBondingdeterminestheSpecificityofbasepairing(complimentarity).2’StackinginteractionbetweenbasesdeterminesthestabilityofDNAdoublehelix,hydrogenbondalsocontributestostability.2’ThedoublehelixhasMinorandMajorgrooves.(ABZforms)2’Differences：Primarystructure(buildingblock):2’dNTPvs.rNTP;Tvs.U;double-strandedvs.single-stranded.Secondarystructure:4’DNAhasstabledoublehelicalstructure.(fullcomplimentarity)RNAchainsfoldbackonthemselvestoformlocalregionsofdoublehelixsimilartoA-formDNA.RNAhelixarethebase-pairedsegmentsbetweenshortstretchesofcomplementarysequences,whichadoptoneofthevariousstem-loopstructures,pseudoknots.(inter-andintra-molecularbasepairing)Tertiarystructures:2’DNA:notertiarystructure.RNAcanfoldupintocomplextertiarystructures,becauseRNAhasenormousrotationalfreedominthebackboneofitsnon-base-pairedregions.ComparethechemistryofDNAsynthesisandRNAsynthesis.(5’)(clues:compare=differences+thesame;chemistry=substrate+direction+energy)Differences:(1)DNAsynthesisrequiresdeoxynucleotidetriphosphateswhileRNAsynthesisrequiresoxynucleotidetriphosphates;(1')(2)ThebaseforDNAsynthesisareA/T/C/GwhilethatforRNAsynthesisareA/U/C/G;(1')(3)DNAsynthesisneedsaprimer:templatejunctionwhileRNAsynthesisdonot;(1')Thesame:(1)ThedirectionofbothDNAsynthesisandRNAsynthesisis5'to3';(1')(2)TheenergyneededforDNAsynthesisaswellasRNAsynthesisishydrolysisofpyrophosphate(PPi).(1')DescribethefunctionsofeachdomainoftheDNApolymerase.(14’+1')DNApolymerasepalmdomain(1'):(1)Containstwocatalyticsites,oneforadditionofdNTPs(1')andoneforremovalofthemispaireddNTP.(1')(2)Thepolymerizationsite:(1)bindstotwometalionsthatalterthechemicalenvironmentaroundthecatalyticsiteandleadtothecatalysis.(1')(2)Monitorstheaccuracyofbase-pairingforthemostrecentlyaddednucleotidesbyformingextensivehydrogenbondcontactswithminorgrooveofthenewlysynthesizedDNA.(1')(3)Exonucleasesite/proofreadingsite.Themechanismofproofreadingiskineticselectivity(1')andthemismatcheddNMPisremovedbyproofreadingexonucleaseinthedirectionof3'-5'(1').DNApolymerasefingerdomain:(1')(1)BindstotheincomingdNTP,enclosesthecorrectpaireddNTPtothepositionforcatalysis;(1')(2)Bendsthetemplatetoexposetheonlynucleotideatthetemplatethatreadyforformingbasepairwiththeincomingnucleotide;(1')(3)Stabilizationofthepyrophosphate;(1')DNApolymerasethumbdomain:(1')(1)Notdirectlyinvolvedincatalysis;(2)InteractswiththesynthesizedDNAtomaintaincorrectpositionoftheprimerandtheactivesite,(1')andtomaintainastrongassociationbetweenDNAPolanditssubstrate.(1')HowreplicationofaDNAmoleculeisaccomplishedinbacteria?

Initiation:RecognitionandbindingofOriCbyDnaA(initiator)-ATP.Helicase(DnaB)loadingandDnaC(helicaseloader)andDNAunwinding.Elongation:PrimasesynthesizesRNAprimer,andDNAPolymeraseIIIsynthesizesthenewDNAstrand.Elongation:(The"trombone"modelwasdevelopedtoexplainlaggingstrandandleadingstrandsynthesizedsimultaneously):Leadingstrand:newlysynthesizedDNAstrandthatiscontinuouslycopiedfromthetemplatestrandbyaDNApolymeraseafterthefirstRNAprimerwasmadebyaprimase.AslidingclampisusuallyloadedtotheDNApolymerasetoincreasethepolymeraseprocessivity.The3directionoftheingstrandisthesameasthemovingdirectionofthereplicationfork.Laggingstrandisdiscontinuouslycopiedfromthetemplatestrand.The3directionofthelaggingstrandisoppositetothemovingdirectionofthereplicationfork.PrimasemakesRNAprimersperiodicallyafterthetemplatestrandisunwoundandbecomessingle-stranded.DNApolymeraseextendseachprimertosynthesisshortDNAfragments,calledOkazakifragments.ThepolymerasedissociatesfromthetemplatestrandwhenitmeetsthepreviousOkazakifragment.Finally,RNAprimersaredigestedbyanRNaseHactivity,andthegapsarefilledbyDNApolymerase.Atlast,theadjacentOkazakifragmentsarecovalentlyjoinedtogetherbyaDNAligasetogenerateacontinuous,intactstrandofnewDNA.Termination:TypeIItopoisomerasesseparatedaughterDNAmolecules.8.HowtranscriptionofaRNAmoleculebyRNApolymeraseIIisinitiated,elongatedandterminatedineukaryotes(25’)Initiation:(11’+附加分)1.Promoterrecognition:TBPinTFIIDbindstotheTATAbox；(1’)TFIIAandTFIIBarerecruitedwithTFIIBbindingtotheBRE；(1’).RNAPolIIrecruitment:RNAPolII-TFIIFcomplexistherecruited；(1’).TFIIEandTFIIHthenbindupstreamofPolII(toformthepre-initiationcomplex).(1()如果提到了pre-initiationcomplex,有1分的附加分)PromotermeltingusingenergyfromATPhydrolysisbyTFIIH.(2’)PromoterescapesafterthephosphorylationoftheCTDtail.(2’)Additionalproteinsareneededfortranscriptioninitiationinvivo:Themediatorcomplex(1)Transcriptionalregulatoryproteins(1)Nucleosome-modifyingenzymes(1’)Tips:1、題目已經(jīng)問(wèn)了是真核中的情況，所以必須把相關(guān)的真核里的factor都回答出來(lái)，不然沒(méi)分；2、B和C兩點(diǎn)非常重要，分值也很大，由此可見(jiàn)把握keypoints的重要性；3、很少同學(xué)可以回答出invivo狀態(tài)下所需要的3種蛋白；4、如果可以答出另外一些細(xì)節(jié)，比如“TBPbindstoanddistortsDNAusingapsheetinsertedintotheminorgroove”，會(huì)有少量加分。Elongation:(7’附+加分)InitiationfactorsarereplacedbyanewsetoffactorsforelongationandRNAprocessing.(或者回答PolIIshedmostofthepreviousfactorsandrecruitothernewfactors)(3’)ThoseelongationfactorsincludeP-TEFbandTFIIS.(如果可以答出factor具體名字，有1分的附加分)RNAprocessingfactorsarealsorecruitedtoPolII.(1’C)ertainfactorsareresponsibleforthecappingofthe5’endoftheRNA(1’)andpolyadenylationofthe3’end,(1)’respectively.Andsplicingfactorscanremoveintrons.(1’)PolIIalsoneedsfactorstodealwithhistonestructures」提到這點(diǎn)會(huì)有1分的附加分)Tips:1、不管怎樣組織語(yǔ)言回答，一定要體現(xiàn)newfactorREPLACE這層意思，提到replace或相同意思就給3分(由此可見(jiàn)把握keypoints的重要性)；2、P-TEFbandTFIIS相關(guān)細(xì)節(jié)內(nèi)容可能很多，但不需要回答太多。縱然把相關(guān)的detail全部回答出來(lái)，也就只算是1個(gè)細(xì)節(jié)，只附加1-2分；3、RNAprocessing相關(guān)內(nèi)容非常重要，有些同學(xué)完全沒(méi)有提到這方面；4、如果回答出相關(guān)的其他細(xì)節(jié)，比如 capping的機(jī)制，CPSF和CstF相關(guān)因子等，一個(gè)細(xì)節(jié)附加1分。Termination: (7’)Theprocessofterminationcoupleswithpolyadenylation.(1’)Terminationincludestwosteps:mRNArelease;(2’)PolIIdissociation:Therearetwopossiblemodels.Torpedomodel:ThesecondRNAmoleculewithoutacapisrecognizedanddegradedbyapossessiveRNase，thusPolIIisthendissociatedfromDNAtemplate.(2’)Allostericmodel:Thetransferofthe3’processingenzymetoPolIIinducesconformationalchange,thusreducingRolIIprocessivity,andspontaneousterminationoccurs.(2’)Tips:1、要明確的指出mRNA被release掉了，這點(diǎn)很少同學(xué)指出；2、很多同學(xué)把termination的兩個(gè)model回答成了Rho-dependent和Rho-independent，這是原核細(xì)胞中的機(jī)制；3、需要把兩個(gè)model的具體含義都回答出來(lái)，如果僅僅提到名字只給2分?？偟腡ips:1、一定要把握keypoints，就是答到“點(diǎn)子”上去，比如“promoterescape”，“newfactorreplace”就是非常重要的關(guān)鍵，會(huì)占較大比重的分值；2、面對(duì)這種大綜合題，細(xì)節(jié)的回答可以為你贏得extrapoints，但是請(qǐng)盡量列舉“不同”的細(xì)節(jié)。如果總是圍繞一個(gè)細(xì)節(jié)闡述很多，終究算一個(gè)細(xì)節(jié)，不會(huì)得到更多的分?jǐn)?shù)。.Howdoesapre-mRNAintrongetspliced?WhatisthedifferencebetweengroupIIintronsplicingandpre-mRNAintronsplicing?(15’)Howpre-mRNAgetspliced:Step1,formationoftheE(early)complexbyrecognitionofthe5'splicesite,3'splicesiteandAbranchpointbyU1snRNP,U2AFandBBPrespectively.Step2,U2snRNPbindtothebranchsitetoreplaceBBPformsAcomplex.Thebase-pairingbetweenU2snRNAwiththebranchsitemaketheconservedAresidueinthebranchsiteextrudedfromthepairedregion,andthusthisAisreadytocarrythenucleophileattack.Thetri-snRNPU4/U6/U5joinsandAcomplexisarrangedtoBcomplexinwhichthethreesplicesitesarebroughttogether.InthiscomplexU4/U6snRNPsareheldtogethertightlybyextensivebase-pairingbetweenU4andU6snRNAs.Step3,U1leavesthecomplex,andU6occupiesthe5'splicesitebybase-pairing.U4leavesthecomplex,allowingtheRNAcomponentsofU2andU6tobasepairtoproducetheactivesite.ThebranchsiteAattacksthe5'splicesite,formingthe3-wayjunctionandCcomplex.The5'splicesitethenattacksthe3'splicesite,freeingtheintronlariatandformingthemRNAproduct.Difference:thechemistryandtheRNAintermediatesproducedarethesameasthatofthespliceosome-mediatedmRNAsplicing,butthesplicingiscatalyzedbytheintronRNAitself,withouttheaidofproteins..Whatisalternativesplicing?Whyitisimportantforhumanbeing?Howalternativesplicingisregulated?(15’)Alternativesplicing:(4’)Manyprotein-encoded