2023年中科院分子生物学试题库题库完整版

GLOSSARYAbundanceofanmRNAistheaveragenumberofmoleculespercell.AbundantmRNAsconsistofasmallnumberofindividualspecies,eachpresentinalargenumberofcopiespercell.Acceptorsplicingsite—seerightsplicingjunction.Acentricfragmentofachromosome(generatedbybreakage)lacksacentromereandislostcelldivision.Acrocentricchromosomehasthecentromerelocatedneareroneendthantheother.Activesiteistherestrictedpartofaproteintowhichasubstratebinds.Alleleisoneofseveralalternativeformsofageneoccupyingagivenlocusonachromosome.Allelicexclusiondescribestheexpressioninanyparticularlymphocyteofonlyoneallelecodingfortheexpressedimmunoglobulin.Allostericcontrolreferstotheabilityofaninteractionatonesiteofaproteintoinfluencetheactivityofanothersite.Alufamilyisasetofdispersed,relatedsequences,each～300bplong,inthehumangenome.TheindividualmembershaveAlucleavagesitesateachend(hencethename).Alu-equivalentfamilyisthesetofsequencesinamammaliangenomethatisrelatedtothehumanAlufamily.α-AmanitinisabicyclicoctapeptidederivedfromthepoisonousmushroomAmanitaphalloides;itinhibhitstranscriptionbycertaineukaryoticRNApolymerases,especiallyRNApolymeraseII.AmbercodonisthenucleotidetripletUAG,oneofthreecodonsthatcauseterminationofproteinsynthesis.AmbermutaiondescribesanychangeinDNAthatcreatesanambercodonatasitepreviouslyoccupiedbyacodonrepresentinganaminoacidinaprotein.AmbersuppressorsaremutantgenesthatcodefortRNAswhoseanticodonshavebeenalteredsothattheycanrespondtoUAGcodonsaswellasorinsteadoftotheirpreviouscodons.Aminoacyl-tRNAistransferRNAcarryinganaminoacid;thecovalentlinkageisbetweentheNH2groupoftheaminoacidandeitherthe3’-or-2’-OHgroupoftheterminalbaseofthetRNA.Aminoacyl-tRNAsynthetasesareenzymesresponsibleforcovalentlylinkingaminoacidstothe2’or3’-OHpositionoftRNA.Amphipathicstructureshavetwosurfaces,onehydrophilicandonehydrophobic.Lipidsareamphipathic;andsomeproteinregionsmayformamphipathic;andsomeproteinregionsmayformamphipathichelices,withonechargedfaceandoneneutralface.Amplificationreferstotheproductionofadditionalcopiesofachromosomalsequence,foundasintrachromosomalorextrachromoxomalDNA.Anchoragedependencedescribestheneedofnormaleukaryoticcellsforasurfacetoattachtoinordertogrowinculture.Aneuploidchromosomeconstitutiondifferesfromtheusaldiploidconstitutionbylossorduplicationofchromosomesorchromosomalsegments.AnnealingisthepairingofcomplementarysinglestrandsofDNAtoformadoublehelix.Antibodyisaprotein(immunoglobulin)producedbyBlymphocytecellsthatrecognizesaparticularforeign‘antigen,’andthuswtriggerstheimmuneresponse.AnticodingstrandofduplesDNAisusedasatemplatetodirectthesynthesisofRNAthatiscomplementarytoit.Antigenisanymoleculewhoseentryintoanorganismprovokessynthesisofanantibody(immunoglobulin).Antiparallelstrandsofthedoublehelixareorganizedinoppositeorientation,sothatthe5’endofonestrandisaligenedwiththe3’endoftheotherstrand.AntiterminationproteinsallowRNApolymerasetotranscribethroughcertainterminatorsites.ApendonucleasesmakeincisionsinDNAonthe5’sideofeitherapurinicorapyrimidincsites.ApoinducerisaproteinthatbindstoDNAtoswitchontranscriptionbyRNApolymerase.Archebacteriacompriseaminorlineofprokaryotes,andmayhaveintronsinthegenome.Ascusofafunguscontainsatetradoroctadofthe(haploid)spores,representhingtheproductsofasihnglemeiosis.attstiesarethelocionaphageandthebacterialchromosomeatwhichrecombinationintegratesthephageinto.orexcisesitfrom,thebacterialchromosome.Attenuationdescribestheregulationofterminationoftranscriptionthatisinvolvedincontrollingtheexpressionofsomebacterialoperons.Attenuatoristheterminatorsequenceatwhichattenuatiojoccurs.Autogenousconhtroldescribestheactionofageneproductthateitherinhibits(negativeautogenouscontrol)oractivates(positiveautogenouscontrol)expressionofthegenecodingforit.Autonomouscontrollingelementinmaizeisanactivetransposonwiththeabilitytotranspose(cfnonautonomouscontrollingelement).Autoradiographydetectsradioactivelylabeledmoleculesbytheireffectincreatinganimageonpholtographicfilm.Autosomesareallthechromosomesexceptthesexchromosomes;adiploidcellhastwocopiesofeachautosome.Blymphocytes(orBcells)arethecellsresponsibleforsynthesizingantibodies.Backcrossisanother(earlier)termforatestcross.Backmutationreversestheeffectofamutationthathandinactivatedagene;thusitrestoreswildtype.Bacteriophagesarevirusesthatinfectbacteria;oftenabbreviatedasphages.Balbainiringisanextremelylargepuffatabandofapolytenechromosome.BandsofpolytenechromosomesarevisibleasdenseregionsthatcontainthemajorityofDNA;bandsofnormalchromosomesarerelativelymuchlargerandaregeneratedintheformofregionsthatretainastainoncertainchemicaltreatments.Basepair(bp)isapartnershipofAwithTorofCwithGinaDNAdoublehelix;otherpairscanbeformedinRNAundercertaincircumstances.Bidirectionalreplicationisaccomplishedwhentworeplicationforksmoveawayfromthesameoriginindifferentdirections.Bivalentisthestructurecontainingallfourchromatids(tworepresentingeachhomologue)atthestartofmeiosis.Blastodermisastageofinsectembryogenesisinwhichalayerofnucleiorcellsaroundtheembryosurroundaninternalmassofyolk.Blockedreadingframecannotbetranslatedintoproteinbecauseitisinterruptedbyterminationcodons.Blunt-endligationisareactionthatjoinstwoDNAduplexmoleculesdirectlyattheirends.bpisanabbreviationforbasepairs;distancealongDNAismeasuredinbp.BranchmigrationdescribestheabilityofaDNAstrandpartiallypairedwithitscomplementinaduplextoextenditspairingbydisplacingtheresidentstrandwithwhichitishomologous.Breackageandreuniondescribesthemodeofgeneticrecombination,inwhichtwoDNAduplexmoleculesarebrokenatcorrespondingpointsandthenrejoinedcrosswise(involvingformationofalengthofheteroduplexDNAaroundthesiteofjoining).Buoyantdesitymeasurestheabilityofasubstancetofloatinsomestandardfluid,forexample,CsCl.Cbandingisatechniqueforgeneratingstainedregionsaroundcentromeres.Cgenescodefortheconstantregionsofimmunoglobulinproteinchains.CvalueisthetotalamountofDNAinahaploidgenome.CAATboxispartofaconservedsequencelocatedupstreamofthestartpointsofeukaryotictranscriptionunits;itisrecognizedbyalargegroupoftranscriptionfactors.Capisthestructureatthe5’endofeukaryoticmRNA,introducedaftertranscriptonbylinkingtheterminalphosphateof5’GTPtotheterminalbaseofthemRNA.TheaddedG(andsometimessomeotherbases)aremethylated,givingastructureoftheform7MeG5’ppp5’Np…CAP(CRP)isapositiveregulatorproteinactivatedbycyclicAMP.ItisneededforRNApolymerasetoinitiatetranscriptionofcertain(catabolitesensitive)operonsofE.coli.Capsidistheexternalproteincoatofavirusparticle.Cataboliterepressiondescribesthedecreasedexpressionofmanybacterialoperonsthatresultsfromadditionofglucose.ItiscausedbyadecreaseinthelevelofcyclicAMP,whichinturninactivatestheCAPregulator.cDNAisasingle-strandedDNAcomplementarytoanRNA,synthesizedfromitbyreversetranscriptioninvitro.cDNAcloneisaduplexDNAsequencerepresentinganRNA,carriedinacloningvector.Cellcycleistheperiodfromonedivisiontothenext.Cellhybridisasomaticcellcontainingchromosomesderivedfromparentalcellsofdifferentspecies(e.g.aman-mousesomaticcellhybrid),generatingbyfusingthecellstoformaheterokaryoninwhichthenucleisubsequentlyfused.Centriolesaresmallhollowcylindersconsistingofmicrotubulesthatbecomelocatednearthepolesduringmitosis.Theyresidewithinthecentrosomes.Centromereisaconstrictedregionofachromosomethatincludesthesiteofattachmenttothemitoticormeioticspindle(seealsokinetochore).Centrosomesaretheregionsfromwhichmicrotubulesareorganizedatthepolesofamitoticcell.Inanimalcells,eachcentrosomecontainsapairofcentriolessurroundedbyadenseamorphousregiontowhichthemicrotubulesattach.SeealsoMTOC.Molecularchaperoneisaproteinthatisneededfortheassemblyorproperfoldingofsomeotherprotein,butwhichisnotitselfacomponentofthetargetcomplex.ChemicalcomplexityistheamountofaDNAcomponentmeasuredbychemicalassay.ChisequenceisanoctamerthatprovidesahotspotforRecA-mediatedgeneticrecombinationinE.coli.ChistructureisajointbetweentwoduplexmoleculesofDNArevealedbycleavinganintermediateoftwojoinedcirclestogeneratelinearendsineachcircle.ItresemblesaGreekchiinoutline,hencethename.Chiasma(pl.chiasmata)isasiteatwhichtwohomologouschromosomesappeartohaveexchangedmaterialduringmeiosis.Chromatidsarethecopiesofachromosomeproducedbyreplication.Thenameisusuallyusedtodescribethemintheperiodbeforetheyseparateatthesubsequentcelldivision.ChromatinisthecomplexofDNAandproteininthenucleusoftheinterphasecell.Individualchromosomescannotbedistinguishedinit.ItwasoriginallyrecognizedbyitsreactionwithstainsspecificforDNA.Chromocenterisanaggregateofheterochromatinfromdifferentchromosomes.Chromomeresaredenselystaininggranulesvisibleinchromosomesundercertainconditions,especiallyearlyinmeiosis,whenachromosomemayappeartoconsistofaseriesofchromomeres.Chromosomeisadiscreteunitofthegenomecarryingmanygenes.EachchromosomecounsistsofaverylongmoleculeofduplexDNAandanapproximatelyequalmassofproteins.Itisvisibleasamorphologicalentityonlyduringcelldivision.ChromosomewalkingdescribesthesequentialisolationofclonescarryingoverlappingsequencesofDNA,allowinglargeregionsofthechromosometobespanned.Walkingisoftenperformedinordertoreachaparticularlocusofinterest.cis-actinglocusaffectstheactivityonlyofDNAsequencesonitsownmoleculeofDNA;thispropertyusuallyimpliesthatthelocusdoesnotcodeforprotein.cis-actingproteinhastheexceptionalpropertyofactingonlyonthemoleculeofDNAfromwhichitwasexpressed.cisconfigurationdescribestwositesonthesamemoleculeofDNA.cis/transtestassaystheeffectofrelativeconfigurationonexpressionoftwomutations.Inadoubleheterozygote,twomutationsinthesamegeneshowmutantphenotypeintransconfiguration,wild-typeincisconfiguration.Cistronisthegenetiunitdefinedbythecis/transtest;equivalenttogeneibcomprisingaunitofDNArepresentingaprotein.Classswitchingisachangeintheexpressionoftheccregionofanimmunoglobulinheavychainduringlymphocytedifferentiation.Clonedescribesalargenumberofcellsormoleculesidenticalwithasingleancestralcellormolecule.Cloningvectorisaplasmidorphagethatisusedto‘carry’insertedforeignDNAforthepurposesofproducingmorematerialoraproteinproduct.Closedreadingframecontainsterminationcodonsthatpreventitstranslationintoprotein.Coatedvesiclesarevesicleswhosemembranehasonitssurfacealayeroftheproteinclathrin.Coconversionisthesimultaneouscorrectionoftwositesduringgeneconversion.CodingstrandofDNAhasthesamesequenceasmRNA.Codominantallelesbothcontributetothephenotype;neitherisdominantovertheother.Coevolution—seeconcertedevolution.CognatetRNAsarethoserecognizedbyaparticularaminoacy-tRNAsynthetase.Coointegratestructureisproducedbyfusionoftworeplicons,oneoriginallypossessingatransposon,theotherlackingit;thecointegratehascopiesofthetransposonpresentatbothjunctionsofthereplicons,orientedasdirectrepeats.Cold-sensitivemutantisdefectiveatlowtemperaturebutfunctionalatnormaltemlperature.ColonyhybridizationisatechniqueforusinginsituhybridizationtoidentifybacteriacarryingchimericvectorswhoseinsertedDNAishomologouswithsomeparticularsequence.Compatibilitygroupofplasmidscontainsmembersunabletocoexistinthesamebacterialcell.Complementationreferstotheabilityofindependent(nonallelic)genestoprovidediffusibleproductsthatproducewildphenotypewhentwomutantsaretestedintransconfigurationinaheterozygote.Invitrocomplementationassayconsistsofidentifyingacomponentofawid-typecellthatcanconferactivityonanextractpreparedfromamutantcell.Theassayidentifiesthecomponentrenderedinactivebythemutation.Complementationgroupisaseriesofmutationsunabletocomplementwhentestedinpairwisecombinationsintrans;definesageneticunit(thecistron)thatmightbetterbecalledanoncomplexmentationgroup.Complexlocus(ofD.melanogaster)hasgeneticpropertiesinconsistentwiththefunctionofagenerepresentingasingleprotein.Complexlociareusuallyverylarge(>100kb)atthemolecularlevel.ComplexityisthetotallengthofdifferentsequencesofDNApresentinagivenpreparation.Compostietransposonshaveacentralregionflankedoneachsidebyinsertionsequences,eitherorbothofwhichmayenabletheentireelementtotranspose.ConcatemerofDNAconsistsofaseriesofunitgenomesrepeatedintandem.ConcatenatedcirclesofDNAareinterlockedlikeringsoneachain.Concertedevolutiondescribestheabilityoftworelatedgenestoevolvetogetherasthoughconstitutingasinglelocus.Condensationreactionisoneinwhichacovalentbondisformedwithlossofawatermolecule,asintheadditionofanaminoacidtoapolypeptidechain.Conditionallethalmlutationskillacellorvirusundercertain(nonpermissive)conditions,butallowittosurviveunderother(permissive)conditions.Conjugationdescribes‘mathing’betweentwobacterialcells,when(partof)thechromosomeistransferredfromonetotheother.Consensussequenceisanidealizedsequenceinwhicheachpositionrepresentsthebasemostoftenfoundwhenmanyactualsequencesarecompared.ConservativerecombinationinvolvesbreakageandreunionofpreexistingstrandsofDNAwithoutanysynthesisofnewstretchesofDNA.Conservativetranspositionreferstothemovementoflargeelements,originallyclassifiedastransposons,butnowconsideredtobeepisomes.Themechanismofmovementresemblesthatofphagelambda.ConstantregionsofimmunoglobulinsarecodedbyCgenesandarethepartsofthechainthatvaryleast.Thoseofheavychainsidentifythetypeofimmunoglobulin.ConstitutivegenesareexpressedasafunctionoftheinteractionofRNApolymerasewiththepromoter,withoutadditionalregulation;sometimesalsocalledhouseholdgenesinthecontextofdescribingfunctionsexpressedinallcellsatalowlevel.Constitutiveheterochromatindescribestheinertstateofpermanentlynonexpressedsequences,usuallysatelliteDNA.Constitutivemutationscausegenesthatusuallyareregulatedtobeexpressedwithoutregulation.Contractileringisaringofactinfilamentsthatformsaroundtheequatorattheendofmitosisandisresponsibleforpinchingthedaughtercellsapart.Controllingelementsofmaizearetransposableunitsoriginallyidentifiedsolelybytheirgeneticproperties.Theymaybeautonomous(abletotransposeindependently)ornonautonomous(abletoelement).Coordinateregulationreferstothecommoncontrolofagroupofgenes.Cordycepinis3’deoxyadenosine,aninhibitorofpolyadenylationofRNA.CoreDNAisthe14.6bpofDNAcontainedonacoreparticle.Coreparticleisadigestionproductofthenucleosomethatretainsthehistoneoctamerandhas14.6bpofDNA;itsstructureappearssimilartothatofthenucleosomeitself.Corepressorisasmallmoleculethattriggersrepressionoftranscriptionbybindingtoaregulatorprotein.Cosmidsareplasmidsintowhichphagelambdacossiteshavebeeninserted;asaresult,theplasmidDNAcanbepackagedinvitrointhephagecoat.CotistheproductofDNAconcentrationandtimeofincubationinareassociationreaction.CotistheCotrequiredtoproceedtohalfcompletionofthereaction;itisdirectlyproportionaltotheuniquelengthofreassociatingDNA.Cotransfectionisthesimultaneoustransfectionoftwomarkers.Crossing-overdescribesthereciprocalexchangeofmaterialbetweenchromosomesthatoccursduringmeiosisandisresponsibleforgeneticrecombination.Crossoverfixationreferstoapossibleconsequenceofunequalcrossing-overthatallowsamutationinonememberofatandemclustertospreadthroughthewholecluster(ortobeeliminated).CruciformisthestructureproducedatinvertedrepeatsofDNAiftherepeatedsequencepairswithitscomplementonthesamestrand(insteadofwithitsregularpartnerintheotherstrandoftheduplex).CrypticsatelliteisasatelliteDNAsequencenotidentifiedassuchbyaseparatepeakonadensitygradient;thatis,itremainspresentinmain-bandDNA.ctDNAischloroplastDNA.CyclicAMP(cAMP)isamoleculeofAMPinwhichthephosphategroupisjoinedtoboththe3’and5’positionsoftheribose;itsbindingactivatestheCAP,apostiveregulatorofprokaryotictranscription.Cyclinsareproteinsthataccumulatecontinuouslythroughoutthecellcycleandarethendestroyedbyproteolysisduringmitosis.(seealsoMPF).Cytokinesisisthefinalprocessinvolvedinseparationandmovementapartofdaughtercellsattheendofmitosis.Cytologicalhybridization—seeinsituhybridization.Cytoplasmdescribesthematerialbetweentheplasmamembraneandthenucleus.Cytoplasmicinheritanceisapropertyofgeneslocatedinmitochondriaorchloroplasts(orpossiblyotherextranuclearorganelles).CytoplasmicproteinsynthesisistheranslationofmRNAsrepresentingnucleargenes;itoccursviaribosomesattachedtothecytoskeleton.Cytoskeletonconsistsofnetworksoffibersinthecytoplasmoftheeukaryoticcell.Cytosoldescribesthegeneralvolumeofcytoplasminwhichorganelles(suchasthemitochondria)arelocated.DloopisaregionwithinmitochondrialDNAinwhichashortstretchofRNAispairedwithonestrandofDNA,displacingtheorignalpartnerDNAstrandinthisregion.ThesametermisusedalsotodescribethedisplacementofaregionofonestrandofduplexDNAbyuasingle-strandedinvaderinthereactioncatalyzedbyRecAprotein.Degeneracyinthegeneticcodereferstothelackofaneffectofmanychangesinthethirdbaseofthecodonontheaminoacidthatisrepresented.DeletionsaregeneratedbyremovalofasequenceofDNA,theregionsoneithersidebeingjoinedtogether.DenaturationofDNAorRNAdescribesitsconversionfromthedouble-strandedtothesinglestrandedstate;separationofthestrandsismostoftenaccomplishedbyheating.Denaturationofproteindescribesitsconversionfromthephysiologicalconformationtosomeother(inactive)conformation.Derepressedstatedescribesagenethatisturnedon.Itissynonymouswithinducedwhendescribingthenormalstateofagene;ithasthesamemeaningasconstitutiveindescribingtheeffectofmutation.Dicentricchromosomeistheproductoffusingtwochromosomefragments,eachofwhichhasacentromere.Itisunstableandmaybebrokenwhenthetwocentromeresarepulledtooppositepolesinmitosis.Diploidsetofchromosomescontainstwocopiesofeachautosomeandtwosexchromosome.Directrepeatsareidentical(orrelated)sequencespresentintwoormorecopiesinthesameorientationinthesamemoleculeofDNA;theyaernotnecessarilyadjacent.DiscontinuousreplicationreferstothesynthesisofDNAinshort(Okazaki)fragmentsthatarelaterjoinedintoacontinuousstrand.Disjunctiondescribesthemovementofmembersofachromosomepairtooppositepolesduringcelldivision.Atmitosisandthesecondmeioticdivision,disjunctionappliestosisterchromatids;atfirstmeioticdivisionitappliestosisterchromatidpairs.DivergenceisthepercentdifferenceinnucleotidesequencebetweentworelatedDNAsequencesorinaminoacidsequencesbetweentwoproteins.Divergenttranscriptionreferstotheintitiationoftranscriptionattwopromotersfacingintheoppositedirection,sothattranscriptionproceedsawayinbothdirectionsfromacentralregion.dnamutantsofbacteriaaretemperature-sensitive;theycannotsynthesizeDNAat42℃,butcandosoat37℃.DNAaseisanenzymethatattacksbondsinDNA.DNA-drivenbybridizationinvolvesthereactionofanexcessofDNAwithRNA.DNApolymeraseisanenzymethatsynthesizesadaughterstrand(s)ofDNA(underdirectionfromaDNAtemplate).Maybeinvolvedinrepairorreplication.DNAreplicaseisaDNA-synthesizingenzymerequiredspecificallyforreplication.Domainofachromosomemayrefereithertoadiscretestructuralentitydefinedasaregionwithinwhichsupercoilingisindependentofotherdomains;ortoanextensiveregionincludinganexpressedgenethathasheightenedsensitivitytodegradationbytheenzymeDNAaseI.Domainofaproteinisadiscretecontinuouspartoftheaminoacidsequencethatcanbeequatedwithaparticularfunction.Dominantalleledeterminesthephenotypedisplayedinaheterozygotewithanother(recessive)allele.Donorsplicingsite—seeleftsplicingjunction.Downpromotermutationsdecreasethefrequencyofinitiatonoftranscription.Downstreamidentifiessequencesproceedingfartherinthedirectionofexpression,forexample,thecondingregionisdownstreamoftheinitiationcondon.EarlydevelopmentreferstotheperiodofaphageinfectionbeforethestartofDNAreplication.Extopicexpressiondescribestheexpressionofageneinatissueinwhichitisnotusuallyexpressed;forexample,inatransgenicanimal.Elongationfactors(EFinprokaryotes,eEFineukaryotes)areproteinsthatassociatewithribosomescyclically,duringadditionofeachaminoacidtothepolypeptidechain.Endlabelingdescribestheadditionofaradioactivelylabeledgrouptooneend(5’or3’)ofaDNAstrand.End-productinhibitiondescribestheabilityofaproductofametabolicpathwaytoinhibittheactivityofanenzymethatcatalyzesanearlystepinthepathway.Endocytosisisaprocessbywhichproteinsatthesurfaceofthecellareinternalized,beingtransportedintothecellwithinmembranousvesicles.Endocyticvesiclesaremembranousparticlesthattransportproteinsthroughendocytosis;alsoknownasclathrin-coatedvesicles.Endonucleasescleavebondswithinanucleicacidchain;theymaybespecificforRNAorforsinglestrandedofdouble-strandedDNA.Endoplasmicreticulumisahighlyconvolutedsheetofmembranes,extendingfromtheouterlayerofthenuclearenvelopeintothecytoplasm.Enhancerelementisacis-actingsequencethatincreasestheutilizationof(some)eukaryoticpromoters,andcanfunctionineitherorientationandinanylocation(upstreamordownstream)relativetothepromoter.Envelopessurroundsomeorganelles(forexample,nucleusormitochondrion)andconsistofconcentricmembranes,eachmembraneconsistingoftheusuallipidbilayer.Epigeneticchangesinflurencethephenotypewithoutalteringthegenotype.Theyconsistofchangesinthepropertiesofacellthatareinheritedbutthatdonotrepresentachangeingeneticinformation.EpisomeisaplasmidabletointegrateintobacterialDNA.Epistasisdescribesasituationinwhichexpressionofonegenewipesoutthephenotypiceffectsofanothergene.Essentialgeneisonewhosedeletionsislethaltotheorganism(seealsolethallocus).Establishedcelllinesconsistofeukaryoticcellsthathavebeenadaptedtoindefinitegrowthinculture(theyaresaidtobeimmortalized).Eubacteriacomprisethemajorlineofprokaryotes.Euchromatincomprisesallofthegenomeintheinterphasenucleusexceptfortheheterochromatin.Evolutionaryclockisdefinedbytherateatwhichmutationsaccumulateinagivengene.Excision-repairsystemsremoveasingle-strandedsequenceofDNAcontainingdamagedormispairedbasesandreplaceitintheduplexbysynthesizingasequencecomplementarytotheremainingstrand.Exocytosisistheprocessofsecretingproteinsfromacellintothemedium,bytransportinmembranousvesiclesfromtheendoplasmicreticulum,throughtheGolgi,tostoragevesicles,andfinally(uponaregulatorysignal)throughtheplasmamembrane.Exocyticvesicles(alsosecretoryvesicles)aremembranousparticlesthattransportandstoreproteinsduringexcytosis.ExonisanysegmentofaninterruptedgenethatisrepresentedinthematureRNAproduct.Exonucleasescleavenucleotidesoneatatimefromtheendofapolynucleotidechain;theymaybespecificforeitherthe5’or3’endofDNAorRNA.Expressionvectorisacloningvectordesinedsothatacodingsequenceinsertedataparticularsitewillbetranscribedandtranslatedintoprotein.Extranucleargenesresideoutsidethenucleusinorganellessuchasmitochondriaandchloroplasts.Ffactorisabacterialsexorfertilityplasmid.F1generationisthefirstgenerationproducedbycrossingtwoparental(homozygous)lines.Facultativeheterochromatindescribestheinertstateofsequencesthatalsoexistinactivecopies—forexample,onemammalianXchromosomeinfemales.FastcomponentofareassociationreactionisthefirsttoreatureandcontainshighlyrepetitiveDNA.Fatemapisamapofanembryoshowingtheadulttissuesthatwilldevelopfromthedescendantsofcellsthatoccupyparticularregionsoftheembryo.FigureeightdescribestwocirclesofDNAlinkedtogetherbyarecombinationeventthathasnotyetbeencompleted.FilterhybridizationisperformedbyincubatingadeaturedDNApreparationimmobilizedonanitrocellulosefilterwithasolutionofradioactivelylabeledRNAorDNA.FingerprintofDNAisapatternofpolymorphicrestrictionfragmentsthatdifferbetweenindividualgenomes.Fingerprintofaproteinisthepatternoffragments(usuallyresolvedonatwodimensionalelectrophoreticgel)generatedbycleavagewithanenzymesuchastrypsin.Fluidityisapropertyofmembranes;itindicatestheabilityoflipidstomovelaterallywithintheirparticularmonolayer.Focusformationdescribesth