Karp Ch 11 细胞生物学英文版 11 章.docx
- 文档编号:11210048
- 上传时间:2023-02-25
- 格式:DOCX
- 页数:63
- 大小:66.16KB
Karp Ch 11 细胞生物学英文版 11 章.docx
《Karp Ch 11 细胞生物学英文版 11 章.docx》由会员分享,可在线阅读,更多相关《Karp Ch 11 细胞生物学英文版 11 章.docx(63页珍藏版)》请在冰豆网上搜索。
KarpCh11细胞生物学英文版11章
Chapter11
ExpressionOfGeneticInformation:
FromTranscriptionToTranslation
Objectives
▪Definetherelationshipbetweengenesandpolypeptides.
▪Describetheflowofinformationthroughcellsandthecellcomponentsthatparticipate.
▪Elaborateonwhatisknownaboutthefinestructureofthegeneinprokaryotesandeukaryotes.
▪Pointoutthedifferencesbetweentranscriptioninprokaryotesandeukaryotes.
▪OutlinetheprocessbywhichrRNAandtRNAareprocessedtotheirmatureforms.
▪DefineheterogeneousnuclearRNAsanddescribetheprocessbywhichtheyareconvertedtomaturemRNA.
▪DescribethestructureofmRNA,the5'capandthepoly(A)tail.
▪Summarizesomeoftheexperimentsthatleduptothediscoveryofthesplitgene.
▪Emphasizetheproposedimportanceofthesplitgenetoevolution.
▪SummarizetheprocessingofhnRNAtomaturemRNA,emphasizingtheremovalofintronsandsplicingtogetherofexons.
▪SummarizethediscoveryofribozymeinvolvementinRNAprocessingandproteinsynthesis.
▪Explainthemechanismsbywhichribozymescarryoutcatalysis.
▪Describethepropertiesofthegeneticcode,itstheoreticalunderpinningsandthecodonassignments.
▪DefinetheroleoftRNAsindecodingthegeneticcode.
▪Summarizethestepsinallstagesoftranslation:
tRNAcharging,initiation,elongationandtermination.
LectureOutline
TheRelationshipBetweenGenesandProteins
I.ArchibaldGarrod(Scottishphysician,1908)–reportedthatcertainrareinheriteddiseasescausedbyabsenceofspecificenzymes
A.Alcaptonuria-urinegetsdarkuponexposuretoair;lackenzymethatoxidizeshomogentisicacid
1.Homogentisicacidformedduringbreakdownoftheaminoacidsphenylalanine&tyrosine
2.Excesshomogentisicacidisexcretedintourine&oxidizesinair,turningblack
B.Calledsuchdiseasesinbornerrorsofmetabolism-ignoredfordecades;hehaddiscoveredconnectionbetweenageneticdefect,aspecificenzyme,andaspecificmetaboliccondition
II.GeorgeBeadle&EdwardTatum(Caltech,1940s)-usedNeurospora,tropicalbreadmold,whichgrowsinsinglecarbonsource(asugar),inorganicsalts,&biotin(aBvitamin)-asimplemedium
A.Neurosporamakesallitsrequiredmetabolites-irradiationdestroysabilitytomakesomeofthem
1.Irradiatemoldspores&culturethem,creatingindividualcellpopulationswithmutatedgenes
2.ScreenformutationbygrowingsporesonminimalmediumthatlackedessentialcompoundsknowntobesynthesizedbyNeurospora
3.Ifsporecannotgrowinminimalmedium,butitcangrowinmediumsupplementedwithacertaincoenzyme,thenthecellshaveanenzymaticdeficiencypreventingsynthesisofthiscompound
4.Foundspecificmetabolicdeficienciesresultingfromsuchenzymedeficiencies
5.Suggeststhatagenecarriestheinformationfortheconstructionofaparticularenzyme
B.Formulatedonegene-oneenzymehypothesis
1.Sinceenzymesoftenhave>1chain,modifiedittoonegene-onepolypeptidehypothesis
2.Onegenenowshowntobeabletobespliceddifferentlytogeneratevarietyofrelatedpolypeptides
III.VernonIngram(Cambridge,1956)-cleavednormal&sicklecellhemoglobinintospecificpieceswithtrypsin(~30fragments)
A.Didpaperchromatographytodistinguishfragments—>onefragmentinsicklecellpreparationmigrateddifferently
B.Differenceisvalinesubstitutioninmutantsicklecellhemoglobinforglutamicacidinnormalmolecule
1.Thisdifferencewasapparentlyresponsibleforallofthesymptomsassociatedwiththedisease
AnOverviewoftheFlowofInformationThroughtheCell
I.TheRNAintermediatethatcarriesgeneticinformationtocytoplasmismessengerRNA[mRNA]
A.ExistenceofmRNAwasfirstdemonstratedin1961byFrançoisJacob&JacquesMonod(PasteurInstitute,Paris)
B.mRNAiscomplementarycopyof1of2DNAstrandsingene(byprocesscalledtranscription)
1.Sinceitssequenceiscomplementarytothatofthegenefromwhichitistranscribed,itcarriesthesameinformationasthegeneitself
2.Allowsseparationofinformationstorage(inhuge,immobileDNA)&informationutilization(smaller,moremobileRNAthatpassesintocytoplasm)
C.Genestayssafe,whileworkingmRNAcopyservesastemplatetodirectincorporationofaminoacidsintoprotein(mRNAisrelativelyunstable;itshalf-lifeisshort,typicallymeasuredinhours)
1.mRNAcodereadduringtranslationbyribosomesincytoplasm(large&smallsubunits)
2.Ribosomesubunitsjoinwhenproteinsynthesisstarts;separatewhenitends
3.Ribosomesmadeofprotein&ribosomalRNA(rRNA;playsstructural&catalyticrole)
4.RibosomescantranslateinformationencodedbyanymRNA;bacterialribosomescanreadhumanmRNAs&makehumanthecorrecthumanpolypeptide
D.ManymRNAsmadefromonegene&manyproteinsfromeachmRNA–amplifiesoutputfromgene
II.rRNAsmadefromoneofDNAstrandsingene;don’tserveinformationalpurposelikemRNA
A.Adaptedtorecognize&bindothermolecules
B.Providestructuralsupport
C.Catalyzechemicalreactioninwhichaminoacidsarecovalentlylinkedtoeachother
III.TransferRNAs(tRNAs)-helpconvertDNAlanguagetothatofaminoacids
A.tRNAs&rRNAshavelonghalf-lifeincell(typicallymeasuredindays)
B.LikerRNAs,tRNAshavecomplexsecondary&tertiarystructures,whichgivethemfunction
1.RNAsfoldintocomplex3Dshapes,whichdiffermarkedlyfromonetypetoanother
2.RNAscarryoutadiversearrayoffunctionsbecauseoftheirdifferentshapes
3.RNAfoldingisdeterminedbyformationofcomplementarybasepairregions(doublestranded&doublehelicalstems)&single-strandedregions(loops)
4.RNAsoftencontainnonstandardmismatchedbasepairs&modifiednitrogenousbasesthatserveasrecognitionsitesforproteins&otherRNAs
Transcription:
TheBasicProcess
I.TranscriptiondonebyDNA-dependentRNApolymerasesinbothprokaryotes&eukaryotes;incorporatenucleotidestomakeRNAfromDNAtemplate;DNAprovidesinformationforRNAstrandsynthesis
II.BeginswithassociationofRNApolymerase&DNAtemplate
A.RNApolymerasesbindtositesonDNAcalledpromotersbeforestartingtranscription;theycannotrecognizepromotersontheirownbutrequirehelpofotherproteins(transcriptionfactors)
1.Transcriptionfactors(TFs)areparticularlyimportantininitiationofeukaryoticgenetranscription
B.Promoteralsocontainsinformationspecifyingwhichstrandtotranscribe&wheretobegin
III.PolymerasemovesalongDNAin3'—>5'directionlayingdowncomplementaryRNAin5'—>3'direction,unwindingDNAtemporarilyasittravelsalongDNAtemplate
A.Catalyzesreaction:
RNAn+NPPP—>RNAn+1+PPi(—>2Pi)
B.Suchreactionsmustbeessentiallyirreversibleunlikemanyreactionsofintermediarymetabolism
1.Topreventreversereaction,nucleicacidsynthesisiscoupledtoexergonicpyrophosphatehydrolysis;donebypyrophosphatase;releaseslargeamountoffreeenergy
2.NucleotideisincorporatedintoRNAstrandifitformsproperWatson-CrickbasepairwithitsoppositenumberintheDNAstrandbeingtranscribed
C.DNAhelixclosesbehindpolymerase;onlyafew(~8)RNAnucleotidesattachedtoDNAatatime
D.BacterialRNApolymerasecanincorporate50-100nucleotides/sec;mostgenesincelltranscribedatsametimebynumerouspolymerases
IV.EnzymemuststayonDNAforlongtimetomakeprodigiouslylongmRNAsbutbelooseenoughtomove;enzymeisprocessive
A.Movementissimilartocytoskeletalmotorkinesin;studiesconfirmthis–attachasingleRNApolymerasemoleculetosurfaceofglasscoverslip
1.AllowRNApolymerasetotranscribeDNAwithfluorescentbeadcovalentlylinkedtooneend&monitorbeadmovement
2.Beadfloatsfreeinsolution&itsrangeofmovementisproportionaltolengthofDNAbetweenpolymerase&bead
3.Aspolymerasetranscribestemplate,theDNAstrandisshortened&beadmovementisrestricted
4.Allowsdeterminationoftranscriptionrateofindividualpolymerase&whetherittranscribesDNAinasteadyordiscontinuousmovement
5.Cantrapbeadbyfocusedlaserbeam&varytheforceuntilitisjustsufficienttostopthepolymerasefromcontinuingtranscription
6.Thepolymerasemoveswithaforce>2Xthatofmyosininteractingwithactin
B.EnergycomesfromNPPPprecursorshydrolysisastheyareincorporatedintogrowingRNAchain
V.Enzymesdonotnecessarilymoveinsteady,continuousfashion;maypauseatcertainsites
A.Sometimes,stalledpolymerasemustdigestaway3'endofnewtranscript&resynthesizethemissingportionbeforeitcanmove;someelongationfactorsenhanceenzyme'sabilitiestopassroadblocks
B.Bothactivities(digestion&polymerization)donebyactivesiteofpolymerase
Transcription:
Prokaryotes
I.E.colihassingleRNApolymerase-4subunitsassociatetightlyformingcoreenzyme
A.Purifycoreenzyme,addDNA&ribonucleosidetriphophates—>enzymebindstoDNA&synthesizesRNA(butnotthesameRNAasincell)
1.Itstartssynthesisatinappropriatesites(randomsitesitwouldnormallyhaveignoredinvivo)
B.Purifyaccessorysigma(σ)factor&addittomixbeforepolymeraseattachestoDNA
1.Transcriptionstartsatrightplaces(selectedspecificlocations,notrandomones)
2.σattachmentincreasescoreaffinityforpromotersites&decreasesaffinityforDNAingeneral
3.Oncetranscriptionbegins,σleaves&coreenzymecontinuessynthesis
C.X-raycrystallographyanalysisofbacterialRNApolymerasecorerevealsamoleculeshapedlikeacrabclawwithabroadinternalchannelthatholdsthedoublehelix
1.Apairofjawsgripst
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- Karp Ch 11 细胞生物学英文版 细胞生物学 英文