最新5细菌的遗传和变异e课件PPT.ppt

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1、5细菌的遗传和变异eBacterialGenomicsMicrobialGenomicsPLASMIDSPlasmidsareextrachromosomalgeneticelementscapableofautonomousreplication.AnepisomeisaplasmidthatcanintegrateintothebacterialchromosomeClassificationofPlasmidsTransferpropertiesConjugativeplasmidsNonconjugativeplasmidsPhenotypiceffectsFertilitypl

2、asmid(Ffactor)Bacteriocinogenicplasmids.Resistanceplasmids7factors).Insertionsequences(IS)-Insertionsequencesaretransposablegeneticelementsthatcarrynoknowngenesexceptthosethatarerequiredfortransposition.a.Nomenclature-InsertionsequencesaregiventhedesignationISfollowedbyanumber. e.g.IS1b.Structure

3、InsertionsequencesaresmallstretchesofDNAthathaveattheirendsrepeatedsequences,whichareinvolvedintransposition.Inbetweentheterminalrepeatedsequencestherearegenesinvolvedintranspositionandsequencesthatcancontroltheexpressionofthegenesbutnoothernonessentialgenesarepresent.c.Importancei)Mutation-Thein

4、troductionofaninsertionsequenceintoabacterialgenewillresultintheinactivationofthegene.ii)Plasmidinsertionintochromosomes-Thesitesatwhichplasmidsinsertintothebacterialchromosomeareatornearinsertionsequenceinthechromosome.iii)PhaseVariation-Theflagellarantigensareoneofthemainantigenstowhichtheimmun

5、eresponseisdirectedinourattempttofightoffabacterialinfection.InSalmonellatherearetwogeneswhichcodefortwoantigenicallydifferentflagellarantigens.Theexpressionofthesegenesisregulatedbyaninsertionsequences.Inoneorientationoneofthegenesisactivewhileintheotherorientationtheotherflagellargeneisactive.T

6、hus,Salmonellacanchangetheirflagellainresponsetotheimmunesystems'attack.PhasevariationisnotuniquetoSalmonellaflagellarantigens.Itisalsoseenwithotherbacterialsurfaceantigens.Alsothemechanismofphasevariationmaydifferindifferentspeciesofbacteria(e.g.Neisseria;transformation).Transposons(Tn)-Transpos

7、onsaretransposablegeneticelementsthatcarryoneormoreothergenesinadditiontothosewhichareessentialfortransposition.Nomenclature-TransposonsaregiventhedesignationTnfollowedbyanumber.Structure-Thestructureofatransposonissim