Review for Final Part 2复习.docx
- 文档编号:25973772
- 上传时间:2023-06-16
- 格式:DOCX
- 页数:32
- 大小:31.21KB
Review for Final Part 2复习.docx
《Review for Final Part 2复习.docx》由会员分享,可在线阅读,更多相关《Review for Final Part 2复习.docx(32页珍藏版)》请在冰豆网上搜索。
ReviewforFinalPart2复习
ReviewforFinal-Part2
Chapters10-18and20
HomologousRecombination
Chapter10
Double-strandedbreakscanbecausedby2situations.Whatarethey?
1.ionizingradiation
2.byblockageofareplicationforkduringDNAreplication.
RepairingDSBs
Howcandouble-strandedbreaksberepaired?
Recombinationrepair
Nonhomologousendjoining(NHEJ)
InprokaryoteslikeE.coli,homologousrecombinationisimportantfor:
1.repairingdouble-strandedbreaksinDNA
2.restartingreplicationforksthathavecollapsed
3.allowingthechromosomalDNAtorecombinewithDNAthatentersabacteriumthroughtransformation,transduction,orconjugation.
Ineukaryoteshomologousrecombinationisimportantfor:
1.repairingdouble-strandedbreaksinDNA
2.restartingreplicationforksthathavecollapsed
3.properpairingofchromosomesduringmeiosis
4.increasingvariationbyrearrangingthegenesonachromosome
Alleles:
differentformsofagenethathavethesamelocationonhomologouschromosomes.
Shortregionsofthebasepairingformbetweenthe2DNAmoleculesthatarerecombining.Asingle-strandedDNApairswithitscomplementarystrandinthehomologousduplexDNAmolecule.Whatisthiscalled?
Whatarethemismatchescalled?
heteroduplexDNA
Strandinvasionconnectsthe2DNAmoleculesandformsanewstructure.Whatisitcalled?
Hollidayjunction
TheHollidayjunctioncanmovealongtheDNAbybreakingthebondsbetweenthebasepairsandreformingnewbonds.WhatisthenameformovementoftheHollidayjunction?
branchmigration
IntheresolutionsteptheHollidayjunctioniscuttoreleasethestrands.
RecBCDbindstoadouble-strandedbreakandthenmovesalongtheDNAunwindingitandoftenitdestroysthestrandswithitsnucleaseactivity.
RecBCDalsohelpsloadRecAontothesingle-strandedends.RecAisastrand-exchangeprotein.
TheactivityofRecBCDiscontrolledbyspecificDNAsequencescalledchisites
(χsites).Chistandsforcrossoverhotspotinstigator.
WhenRecBCDreachesachisite,itstopsdigestingonestrandtoforma3’tailwiththechisiteattheend.RecAbindstothistailtobeginrecombination.
RecAcatalyzesstrandinvasion.OnceRecAhasformedafilamentonsingle-strandedDNA,itsearchesforhomologous(complementary)sequencesindouble-strandedDNA.
RecAboundto3strandsofDNAiscalledajointmolecule.
WithinthisstructureRecAcatalyzesthebreakingofhydrogenbondsbetweenbasesandforminghydrogenbondswiththesingle-strandedDNA.
IneukaryotesthestrandinvasionaccomplishedbyRecAinbacteriaisperformedbyDmc1andRad51.
2.GeneConversion
Geneconversionisaphenomenoninwhichallelesaresegregatedina3:
1nota2:
2ratioinmeiosis.
Site-SpecificRecombinationandTranspositionofDNA
Chapter11
Thereare2maintypesofgeneticrecombination.Whatarethey?
conservativesite-specificrecombination(CSSR)
transposition
A.ConservativeSite-SpecificRecombination
Conservativesite-specificrecombinationdiffersfromtranspositioninthatshortspecificsequences,aretheonlysitesatwhichrecombinationoccurs.Thesesequencesarecalledrecombinationsites.
Therecombinationsitesarerecognizedbyrecombinase.
1.Recombinases
1.Thereare2familiesofconservativesite-specificrecombinases.Whatarethey?
a.serinerecombinases
b.tyrosinerecombinases
Tointegratethelambdaintegraseprotein(λInt)catalyzesrecombinationbetween2specificsitesnamedattachmentsitesoratt.
TheattPsiteisinthephageDNA,whiletheattBsiteisinthebacterialchromosome.
Lambdaintegrase(λInt)isatyrosinerecombinasethatrecognizesattPandattB.
Aprophagecaninitiatealyticcycle.Thisiscalledinduction.
CertainenvironmentalconditionssuchasUVirradiationcanstimulateinductionoftheprophage.TheUVirradiationactivatesRecA.
RecAcausesautocleavageofλrepressorresultingintranscriptionofthelyticgenes.
B.Transposition
transposableelement:
asequenceofDNAfoundinbothprokaryotesandeukaryotesthatcanmovefromonelocationtoanotherinthegenome.
Bacterialtransposableelementsarecalledtransposons.
Transposition:
movementofatransposableelementtoanewsiteinthegenome
Theenzymethatcatalyzestranspositioniscalledtransposase.
Thereare3kindsoftransposableelementsbasedontheirstructureandmethodoftransposition.Whatarethey?
DNAtransposons
viral-likeretrotransposons
Poly-Aretrotransposons
ADNAtransposonhasinvertedrepeatsattheendsandthecodingsequencefortheenzyme,transposase.
Viral-likeretrotransposonshavelongterminalrepeats(LTR).
Thisoneencodesintegraseandreversetranscriptase(RT).RTisneededbecauseanRNAintermediateisproducedduringreplication.
1.Autonomoustransposableelementscontainafunctionaltransposasegeneandtheseelementscantransposeontheirown.
2.Nonautonomoustransposableelementshavemutationsinthetransposasegeneandaredependentonthetransposasefromanotherelementtotranspose.
Inthecut-and-pastemechanismtransposasebindstotheinvertedrepeatsequencesandbringsthemtogether.
Afterthetransposonisexcised,the3’OHbreaksthephosphodiesterbondsatthenewsiteofinsertion.ThisnewsiteiscalledthetargetDNA.Formosttransposons,thetargetDNAcouldbeanysequence.
Theformationoftargetsiteduplicationsindicatesthatthetransposasemakesastaggeredcutinthetargetsequence.
MechanismsofTranscription
Chapter12
A.Fourrequirementsfortranscription
Thereare4thingsthatarenecessaryfortranscriptionofDNA:
1.templateDNA
2.RNApolymerase
3.promoter
4.4rNTPs
Whatisaholoenzyme?
Aholoenzymeisacomplexofmanysubunitsthathasacoreenzyme,whichhasfunction,butthisfunctionisincreasedbythepresenceofotherproteinsubunits.
b.theholoenzyme
TheholoenzymeofRNApolymerasehasthe4subunitsfromthecoreenzymeplusσ(sigma).
σ(sigma)actsasaspecificityfactor.ItrecognizesthepromotersequencesintheDNA.
WhatisthenameforthemainσfactorinE.coli?
σ70
AconsensussequenceisasequenceofnucleotidesoraminoacidsincommonbetweenregionsofhomologyindifferentbutrelatedDNAorRNAorproteinsequences.Oftenthesequencesofmanydifferentgenesorspeciesarecomparedtoidentifytheconsensussequence.
B.StepsinTranscription
Whatarethethreestepsintranscription?
1.Initiation
2.Elongation
3.Termination
1.Initiation
Thereare3stepsininitiation.Whatarethey?
1.formingtheclosedcomplex
2.formingtheopencomplex
3.additionofthefirstnucleotidesandpromoterescape(lossofsigma)
Thefirstbasepairthatisaddedisusuallyanadenine.TheRNApolymerasebindstotheadenineandholdsitinplaceforanotherribonucleotidetocomeandbindtoit.
Whentheholoenzyme,whichincludestheσ70factor,bindstotheDNA,firstitformstheclosedcomplex.Thentheenzymechangesshape.Thisiscalledisomerization.
Isomerizationmeansareversiblechangeintheconformationofanenzyme.
Whatarethe2mechanismsthatRNApolymerasehasforproofreadingthe
RNA?
a.pyrophosphorolyticediting
b.hydrolyticediting
RemovalofStoppedRNAPolymerases
SometimesanRNApolymerasecanbecomestopped.ThisisusuallycausedbydamagetotheDNA.
Inbacterialtranscription-coupledrepair,TRCFremovesthestoppedRNApolymeraseandrecruitsrepairenzymestothedamagedDNA.UvrBCrepairtheDNA.
3.Termination
Thereare2differentwaysthat
transcriptionofageneterminates?
Whatarethey?
a.rho(ρ)independent
b.rho(ρ)dependent
a.rho(ρ)independent
Rhoindependentterminatorshaveaninvertedrepeatsequence.
Whatisthiscalled?
Palindrome
Apalindromesequenceformsastemandloopstructure.Thisisalsocalledahairpinstructure.
a.RNApolymeraseItranscribesrRNAs—the5.8S,18Sand28SrRNAs.Thisoccursinthenucleolus.
b.RNApolymeraseIIItranscribesthetRNAs,the5SrRNAandtheU6smallnuclearRNA(snRNA).
ThegenestranscribedbyRNApolymeraseIandRNApolymeraseIIIareexpressedineverycell.
Whatarethesecalled?
Thesearehousekeepinggenes.
c.RNApolymeraseIItranscribesallthegenesthatencodeproteins.ItalsotranscribesmostofthesmallnuclearRNAgenes.
Theelementsthatcanbepresentinacorepromoter:
aTATAboxandaninitiator
TFIIDisacomplexofseveralsubunitsincludingaTBP(TATA-box-bindingprotein)and8-10TBPassociatedfactors(TAFs).
4.Post-transcriptionalmodificationsofmRNAoccur.
Whatpost-transcriptionalmodificationsoccurineukaryoticcells?
a.A5’capisaddedtothe5’endofthe
mRNA.
b.ApolyAtailisaddedtothe3’endofthemRNA.
c.TheRNAisspliced.
RNASplicing
Chapter13
RNAsplicingremovestheintronsfromthepre-mRNAtoproduceamaturemRNA.
Alternativesplicingproducesdifferentproteins.Thesearecalledisoforms.
A.TheChemistryofSplicing
Atthe5’endwhereanexonmeetsandintronthereisasequencethatindicatesa5’splicesite.Atthe3’endoftheintronisanothersiteindicatinga3’splicesite.
Besidesthe5’splicesiteandthe3’splicesite,asequencecalledthebranchpointsiteisalsoneeded.
1.StepsinSplicing
Thereare2stepsinsplicinginwhichthephosphodiesterbondsintheRNAarebrokenandreformed.Thereactionsarecalledtransesterifications.
InRNAsplicingthelariatisrapidlydegradedafteritisproducedbythesplicingprocess.
B.TheSpliceosome
Theenzymesthatcatalyzethe2stepsinsplicingformacomplex.Whatisthiscomplexcalled?
spliceosome
EachsmallnuclearRNA(snRNA)isboundbyproteinscalledsmallnuclearribonuclearproteinsorsnR
- 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:
- Review for Final Part 2复习 复习