微生物学,双语教学Chapter,8,Microbial,genetics

Microbialgenetics Chapter8 8 1MutationsandMutants8 2GeneticRecombination8 3GeneticTransation8 4Transduction8 5Conjugation8 6Plasmids8 7TransposonsandInsertionSequences8 8ComparativeProkaryoticGenomics8 9GeneticsinEukaryoticMicroorganisms Microorganismsproviderelativelysimplesystemsforstudyinggeneticphenomenaandarethususefultoolsinattemptstodecipherthemechanismsunderlyingthegeneticsofallorganisms Microorganismsareusedfortheisolationandduplicationofspecificgenesfromotherorganisms atechniquecalledmolecularcloning Inmolecularcloning genesaremanipulatedandplacedinamicroorganismwheretheycanbeinducedtoincreaseinnumber Section1 Mutationandrecombination Mutationisaninheritedchangeinthebasesequenceofthenucleicacidcomprisingthegenomeofanorganism Mutationusuallybringsaboutonlyaverysmallamountofgeneticchangeinacell Geneticrecombinationistheprocessbywhichgeneticelementscontainedintwoseparategenomesarebroughttogetherinoneunit Thismechanismmayenabletheorganismtocarryoutsomenewfunctionandresultinadaptationtochangingenvironments Geneticrecombinationusuallyinvolvesmuchlargerchanges Entiregenes setsofgenes orevenwholechromosomes aretransferredbetweenorganisms Section2 Techniquesofbacterialgenetics invivo Invivo manipulatethegeneticmaterialwithintheorganism GeneticTransationTransductionConjugation Section3 Techniquesofbacterialgenetics invitro Invitro operategeneticmaterialinthetesttube RestrictionEnzymesMolecularCloningAmplifyingDNA PCR AuxotrophanorganismthathasdevelopedanutritionalrequirementthroughmutationCloningvectorgeneticelementintowhichgenescanberecombinedandreplicatedConjugationtransferofgenesfromoneprokaryoticcelltoanotherbyamechanisminvolvingcell to cellcontactandaplasmidDiploidaeukaryoticcellororganismcontainingtwosetsofchromosomesElectroporationtheuseofanelectricpulsetoinducecellstotakeupfreeDNAGenedisruptionuseofgenetictechniquestoinactivateagenebyinsertingwithinitaDNAfragmentcontaininganeasilyselectablemarker Theinsertedfragmentiscalledacassette andtheprocessofinsertion cassettemutagenesis WORKINGGLOSSARY GeneticmapthearrangementofgenesonachromosomeGenomethetotalcomplementofgenesofacelloravirusGenotypetheprecisegeneticmakeupofanorganismHybridizationationofaduplexnucleicacidmoleculewithstrandsderivedfromdifferentsourcesbycomplementarybasepairingMolecularcloningisolationandincorporationofafragmentofDNAintoavectorwhereitcanbereplicatedHaploidacellororganismthathasonlyonesetofchromosomesMutagensagentsthatcausemutationMutantanorganismwhosegenomecarriesamutationMutationaninheritablechangeinthebasesequenceofthegenomeofanorganism NucleicacidprobeastrandofnucleicacidthatcanbelabeledandusedtohybridizetoacomplementarymoleculefrommixtureofothernucleicacidsPhenotypetheobservablecharacteristicsofanorganismPlasmidanextrachromosomalgeneticelementthathasnoextracellularPointmutationamutationthatinvolvesoneoronlyaveryfewbasepairsPolymerasechainreaction PCR ausedtoamplifyaspecificDNAsequenceinvitrobyrepeatedcyclesofsynthesisusingspecificprimersandDNApolymeraseRecombinationtheprocessbywhichpartsoralloftheDNAmoleculesfromtwoseparatesourcesareexchangedorbroughttogetherintoasingleunit Restrictionenzymeanenzymethatrecognizesandmakesdouble strandedbreaksatspecificDNAsequencesShotguncloningmakingagenelibrarybyclosingrandomDNAfragmentsSite directedmutagenesisatechniquewherebyagenewithaspecificmutationcanbeconstructedinvitroSyntheticDNAaDNAmoleculemadebyachemicalprocessinalaboratoryTransductiontransferofhostgenesfromonecelltoanotherbyavirusTransationtransferofbacterialgenesinvolvingfreeDNATransposonatypeoftransposableelementthatcarriesgenesinadditiontothoseinvolvedintransposition GeneticRecombination Geneticrecombinationinvolvesthephysicalexchangeofgeneticmaterialbetweengeneticelements HomologousrecombinationresultsingeneticexchangebetweenhomologousDNAsequencesfromtwodifferentsources Thistypeofrecombinationisextremelyimportanttoallorganisms However itisalsoverycomplex EveninthebacteriumEscherichiacolithereareatleast25genesinvolved Asimplifiedversionofonemolecularmechanismofrecombination HomologousDNAmoleculespairandexchangeDNAsegments Themechanisminvolvesbreakageandreunionofpairedsegments Twooftheproteinsinvolved asingle strandedbinding SSB proteinandtheRecAprotein Notethattherearetwopossibleoutcomes dependingonwhichstrandsarecutduringtheresolutionprocess Inoneoutcometherecombinantmoleculeshavepatches whereasintheotherthetwoparentalmoleculesappeartohavebeencutandthensplicedtogether InordertodetectphysicalexchangeofDNAsegments thecellsresultingfromrecombinationmustbephenotypicallydifferentfromtheparents DetectionofRecombination Strainsthatlacksomeselectablecharacteristicthattherecombinantswillpossess Forinstance therecipientmaynotbeabletogrowonaparticularmedium andgeneticrecombinantsareselectedthatcan Variouskindsofselectableandnonselectablemarkers suchasdrugresistance nutritionalrequirements andsoon maybeused Complementation Thiscanbedeterminedbyatypeofexperimentcalledacomplementationtest Complementationwasfirstuse