微生物的新陈代谢

ChapterfiveMicrobialmetabolismsectionAHeterotrophicpathwayssectionBElectrontransportandoxidativephosphorylationsectionCAutotrophicmetabolismSectionDBiosyntheticpathways,Metabolismisdividedintothosepathwaysthataredegradative(catabolic)andthosethatareinvolvedinsynthesis.Catabolicpathwaysoftenproduceenergy.Microbesthatutilizeorganicmoleculesasasourceofenergyarecalledheterotrophs.Phototrophsobtainenergyfromlight,andlithotrophs(无机营养菌)obtainenergyfrominorganiccompounds.,Keynotes(1),Nutritionaltypes,Metabolisminallcellsisdividedintocatabolic(thosepathwaysinvolvedinbreakdownoforganicmoleculesforenergyandtheproductionofsmallcompoundsthatmaybeusedforsynthesis)andanabolic(pathwaysinvolvedinsynthesis)processes.,Inallorganismsthesepathwaysarebalancedastheenergyrequiredforanabolicprocessesisproducedbycatabolicpathways.,Inmammaliancells,energyproductionhasbeenmaximizedbytheuseofoxygenandthusthecellisusuallywellsuppliedwithenergy;however,inmicrobesthisisnotalwaysthecase.,catabolicandanabolicmetabolism,Microbescanbedividedintometabolicclasseswhichrelatetothesourcesofenergytheyuse.Thethreegroupsare:1.heterotrophswhichutilizeorganicmoleculesasasourceofenergy(thesearealsocalledchemo-organotrophs化能有机营养型);2.phototrophswhichobtainenergyfromlight3.lithotrophswhichobtainenergyfrominorganiccompounds.Carbon(碳素)forcellsynthesisisobtainedfromorganicmolecules;however,somemicrobes,includingthephototrophs,fixCO2.,Microbialmetabolictypes,CatabolismMetabolismanabolismcomplexmoleculesimplemolecules+ATP+H*（Organicmaterial）*Hstandsforreducingpower(还原力)catabolismenzymecomplex（分解代谢酶系）anabolismenzymecomplex（合成代谢酶系）,organicmaterialPrimaryenergysources(最初能源)rayirradiation(light)ChemoheterotrophsreducedinorganicmaterialPhototrophschemoautotrophsuniversalenergysource(通用能源)ATP,Energymetabolism,SectionAHeterotrophicpathwaysBiologicaloxidationisreferredtoasalltheenergy-producingoxidativereactionsinthelivingorganism.,Definition:Aseriesofenergy-producingoxidativereactionsoccursinthelivingcellsarecalledbiologicaloxidation.,Theprocessofbiologicaloxidation(生物氧化的过程)1.Removeofhydrogen(脱氢)2.Transferofhydrogen(递氢)3.Receiveofhydrogen(受氢),Biologicaloxidation(生物氧化）,Functionofbiologicaloxidation(生物氧化的功能)Produceenergy(产能)ProducereducingpowerH(产还原力)Smallintermediatemetabolites(产小分子中间代谢物),Typesofbiologicaloxidation:1.Aerobicrespiration(好氧呼吸)2.Anaerobicrespiration(厌氧呼吸)3.Fermentation(发酵),Pathwaysofremovingofhydrogen:(inthecaseofGlucose)EMP(glycosis)HMP(pentosephosphatepathwayorWD)ED(KDPG)TCAcycle(citricacidcycle),Removing,remove,transfer,receive,（ororganicorinorganicoxide）,（organicorinorganicdeoxide）,FourpathwaysofHremovingfromsubstrate,Mostmicrobesutilizetheglycolytic（糖酵解）pathwayforthecatabolismofcarbohydratessuchasglucoseandfructose.Theproductsofthispathwayarepyruvate,whichcanbefurthermetabolizedviathecitricacidcycle,formingadenosine5-triphosphate(ATP)andthereducedformofnicotinamideadeninedinucleotide(烟酰胺腺嘌呤核苷酸NADH+H+.）Thispathwayislocatedinthecytoplasmofmicrobesandcanfunctioninthepresenceorabsenceofoxygen.,Keynotes(2),Glycolysis(EMPpathway),ThebacterialgeneraPseudomonas,Rhizobium（根瘤菌）andAgrobacter（农杆菌）substitutetheEntner-Doudoroffpathwayfortheglycolyticpathway.Thispathwayisnotasefficientinproducingenergy,with1moleofATPbeingformedforeachmoleofglucosemetabolized.,Keynotes(3),TheEDpathway,ThepentosephosphatepathwayorhexosemonophosphatepathwaymayoperateatthesametimeasglycolysisortheEntner-Doudoroffpathway.Thispathwaycanalsooperateeitherinthepresenceorabsenceofoxygen.Thepentosephosphatepathwayisanimportantsourceofenergyinmanymicroorganisms;however,itsmajorrolewouldseemtobeforbiosynthesis.ThebasicoutlineofthispathwayisshownintheFig.ThepathwayproducesNADPH.,Keynotes(4),pentosephosphatepathway(HMP),Thepentosephosphatepathway（戊糖磷酸途径）producesNADPH+H+andsugars(4C,5C).Thesearerequiredformanysyntheticreactions.Whenorganismsaregrowingonapentose(5C)sugar,thepathwaycanbeusedtoproducecarbohydratesforcell-wallsynthesis.Glyceraldehyde-3-phosphate(三磷酸甘油醛)formedbythepathwaycanbeusedtogenerateenergybyglycolysisorbytheEntner-Doudoroffpathway.,Keynotes(4),pentosephosphatepathway,Themetabolismofpyruvate(formedbyglycolysis)toCO2bythecitricacidcycleisthemajormechanismofATPgenerationinthecellandisalsoanimportantsourceofcarbonskeletonsforbiosynthesis.Thefully（完整的柠檬酸循环途径的功能）functioningpathwayrequiresoxygen;however,someorganismspossessanincompletecyclethatcanfunctioninthepresenceorabsenceofoxygenbutgenerateslittleornoenergy.,Keynotes(5),Citricacidcycle,ManymicrobesuseEMPpathways,althoughenergy-producingefficiencyislow,ithasextremelyimportantphysiologicalfunctions;mostaerobicandfacultativeanaerobicmicrobesusebothHMPandEMPpathways.ThefeatureofitisthatGcanbethoroughlyoxidizedthroughEMPandTCAcycle.EDpathwayisamicrobespecificsubstitutewayreplacesEMPinthosemicrobesthatlacksthefullEMPpathway.,NADH+H+producedbycatabolicreactionssuchasthecitricacidcyclecanbeoxidizedbytheelectron-transportpathwayinthepresenceofoxygen.However,intheabsenceofoxygen,manymicrobesutilizefermentationreactionstoreoxidizeNADH+H+.Microbialfermentationsarecharacterizedbytheendproductsformed.(微生物所进行的各种发酵,常常是以他们所形成的终产物而命名)Clostridia(梭菌则通常通过氨基酸发酵Stickland反应形成ATP)areunusualinthattheyformATPfromthefermentationofammoacidsbytheSticklandreaction.,Keynotes(6),fermentations,ThecitricacidcycleisthemostefficientmechanismforgeneratingATPfromglucoseinthepresenceofoxygen.Formicrobesthatliveinenvironmentswhereoxygenisabsentoronlypresentintermittently,ATPgenerationislessefficient.(生活在厌氧或间歇供氧环境中的微生物,ATP产生的效率是低的),Keynotes(7),ATPyields(产率),Themajorityofmicrobesutilizetheglycolyticpathway(糖酵解途径alsoknownastheEmbden-Meyerhofpathway)forthecatabolismofcarbohydratessuchasglucoseandfructose.Thisseriesofreactionsoccursinthecytoplasmofmicrobesandcanoperateeitheranaerobically(intheabsenceofoxygen)oraerobically(inthepresenceofoxygen).TheoverallequationforthispathwayisGlucose+2ADP+2Pi+2NAD+2pyruvate+2ATP+2NADH+2H+,Glycolysis(糖酵解)EMP,brieffigureofEMPpathway,2stages3products10reactions,Pyr,ATPconsuming,ATPproducing,1.Pyruvateformedbyglycolysiscanbefurthermetabolizedinthepresenceofoxygentogenerateenergyviathecitricacidcycleorcanbeusedforsynthesisofothercompoundssuchasaminoacids.2.Adenosinetriphosphate(ATP)canbeuseddirectlytodriveuptakeofsubstratesorcanbeusedtodrivesyntheticreactions.NADH+H+canbeusedtoproduceenergyviaoxidativephosphorylation(amethodofATPformationthatrequireselectrontransport)orcanbeusedasasourceofH+forreductionreactions.,TheproductofEMPpathway,SomeorganismssuchasthebacteriaClostridiautilizeinorganicpyrophosphate(无机焦磷酸盐)(PPi)inplaceofATPasasourceofenergytodrivetheformationofpyruvatefromphosphoenolpyruvat-e(磷酸烯醇式丙酮酸)andfortheconversionoffructose-6-phosphateintofructose-1,6-bisphos-phate.,Exception,AminorityofbacteriaincludingPseudomonas,RhizobiumandAgrobactersubstitutetheEntner-Doudoroffpathwayfortheglycolyticpathway.Thepathwayyields1moleeachofATP,NADPH+H+andNADH+H+foreachmoleofglucosemetabolized.Theproductsofthispathway,likethoseofglycolysis,canbeusedforavarietyoffunctions;however,theNADPH+H+formedisusedforsyntheticreactions.,EDpathway,EDpathway,ethanol,Pyr,BriefpatternofEDpathway,Inthepresenceofoxygenviarespiratorypathwayfermentationwhileavoidofoxygen,Throughonly4stepsfromG,CharacteristicsofEDpathway:1.FeatuKDPGredbythereactionthatKDPGwascatalyzedintopyruvateandglyceraldehyde-3-phosphate.2.CharacterizedbyanspecialenzymeKDPG醛缩酶3.Twomoleculesofpyruvatescamefromdifferentpathways.4.Lowenergy-yieldingefficiency1molATP/1molG,Thepentosephosphatepathwayorhexosemonophosphatepathway(己糖单磷酸途径)mayoperateatthesametimeasglycolysisortheEntner-Doudoroffpathway.Thispathwaycanalsooperateeitherinthepresenceorabsenceofoxygen.Thepentosephosphatepathwayisanimportantsourceofenergyinmanymicroorganisms;however,itsmajorrolewouldseemtobeforbiosynthesis.,HMPpathway,BreifpatternofHMPpathway,Afteraseriesofreactions,hexoseweresynthesizedagain,ThebasicoutlineofthispathwayisshowninFig.ThepathwayproducesNADPHandsugars(4C,5C),whicharerequiredforthesynthesisofaromaticaminoacidsandnucleotides.Whenorganismsaregrowingonapentose(5C)sugar,thepathwaycanalsobeusedtoproducecarbohydratesforcell-wallsynthesis.Glyceraldehyde-3-phosphate(3-磷酸甘油醛)canbeusedtogenerateenergyviatheglycolytic/Entner-Doudoroffpathways.,Althoughenergyisobtainedfromthebreakdownofpyruvatebyoneofthepreviouspathways,asignificantlygreateryieldcanbeachievedinthepresenceofoxygenfromthefurtheroxidationofpyruvatetoCO2viathecitricacidcyclealsoknownasthetricarboxylicacidcycle.Pyruvatedoesnotenterthispathwaydirectly,itmustfirstundergoconversionintoacetylcoenzymeA(acetylCoA):Pyruvate+NAD+CoAAcetylCoA+NADH+H+Thisreactioniscatalyzedbypyruvatedehydrogenase,alargecomplexcontainingthreeenzymes.,Citricacidcycle(TCA),AcetylCoAcanalsobeproducedbythecatabolismoflipidsandaminoacidsaswellasawiderangeofcarbohydrates.ATPcanbeformedfromNADH+H+byoxidativephosphorylation.Thispathwayisalsoanimportantsourceofcarbonskeletonsforuseinbiosynthesis.Citricacidcycleenzymesarewidelydistributedinmostmicrobesandothermicroorganisms.Functionalandcompletecyclesarefoundinmostaerobicmicrobes,algae,fungiandprotozoa;however,infacultativeorganisms(兼性微生物thosethatcangrowinthepresenceorabsenceofoxygen)thecompletecitricacidcyclewouldonlybefunctionalinthepresenceofoxygen.Manyanaerobicorganismshaveanincompletecycle,whichisusedfortheproductionofsyntheticprecursors.,TCAcycle,12ATP,2ATP,Respiratorychain,Respiratorychain,（substratelevel）ATP,MajorproductsofTCAcycle,carbohydrates,fat,protein,ThecriticalstatusofTCAcycleinthecatabolicandanabolicmetabolism,How38ATPisformedfrom1glucoseviaEMPandTCA？,isEMP，isTCA，isrepirationchain，framedisfinalproduct,CharacteristicsofTCActycle:1.Functioningonlyaerobically(intheprescenceofoxygen),althoughO2isntdirectlyinvolvedin.2.Highenergyyieldingefficientwith4moleofNADH+H+,1moleofFADH2and1moleofGTPwereformedfrom1moleofpyruvate,equally15moleATP.3.Locatedinacriticalandconnectingpointbetweencatabolicandanabolicmetabilism.,substratelevel,netATP,2（about6ATP）,12（about36ATP）,1（about3ATP）,1（about3ATP）,2（about2ATP）,2+8*（about30ATP）,2（about4ATP）,Energy-yieldingefficientofglucoseviadifferentdehydratepathways,SectionBElectrontransportandoxidativephosphorylation,NADH+H+andFADH2formedbycatabolicreactionsareusedtoproduceATPbytheactionofanelectron-transportchainwhichiscomposedofaseriesofelectroncarriers.Inbacteria,electrontransportoccursintheinnercellmembrane(细胞质内膜).Inothermicrobes(eukaryotes),electrontransportoccursintheinnermembraneofthemitochondria.Mostbacterialelectron-transportchainsarebranchedunlikethoseinmammalianmitochondria.,Keynotes:electron-transportchain,Allelectron-transportpathwaysfunctioninasimilarmanner,requiringaseriesofoxidationandreductionreactions.Theoxidationofamoleculeinvolvesthelossofelectrons,andreductioninvolvestheadditionofelectrons.Sinceelectronsareconservedinchemicalreaction,oxidationsmustbecoupledwithreductionreactions(redoxreactions).,Theoxidation-reductionpotential(redoxpotential)ofacompoundisameasureofitsaffinityforelectrons.ThedifferenceinredoxpotentialbetweenNADH+H+/NADand1/2O2/H2OdrivesthemovementofelectronsthroughaseriesofelectroncarriersfromNADH+H+to02.Energyisreleasedaselectronsmovebetweencarriers.ThiscanalsobelinkedtoATPformation.,Thechemiosmotichypothesis(化学渗透学说)isawidelyacceptedtheorythatexplainshowATPisproducedbyelectrontransport.ATPproductionrequiresthatH+moveacrossthemembranewhereelectrontransportoccurs,producingatransmembraneH+gradient.TheH+movesbackacrossthemembraneviaATPsynthase.ThemovementofH+iscoupledwithlargereleasesofenergyassociatedwithelectrontransport,suchthatwhenNADH+H+istheelectrondonorandoxygenistheterminalelectronacceptor,H+movementacrossthemembraneoccursatthreesites.InmicrobeswithshortpathwaysorwhereNADH+H+isnottheelectrondonor,lessATPisproduced.,FormationofATP,NADH+H+andflavinadeninedinucleotide(reducedform)(FADH2)formedbythecatabolismoforganicmoleculesareusedtoproduceATPbytheactionofanelectron-transportchainthatiscomposedofaseriesofelectroncarrierswhichtransferelectronstoaterminalelectronacceptorsuchasoxygen.Thisfinalreductionisperformedbyaterminaloxidase.Oxygenisnottheonlyusefulelectronacceptor.,1.Electron-transportchain(1),Inbacteria,electrontransportoccursintheinnercellmembrane,butinalgae,fungiandmanyprotozoa,electrontransportandoxidativephosphorylationoccurintheinnermembraneofthe.mitochondria.,1.Electron-transportchain(2),Mostbacterialelectron-transportchainsaredifferenttothatfoundinmammalianmitochondriaandmanylikeE.coliarebranched.SomechainsareshortandthisreducestheircapacityforATPproduction.Electronscanenterbacterialelectron-transportchainsatvariouspointsandthisincreasesthenumberofsubstratesthatcanbeusedforATPsynthesis.,1.Electron-transportchain(3),Allelectron-transportpathwaysfunctioninasimilarmanner,requiringaseriesofoxidationandreductionreactions.Theoxidationofamoleculeinvolvesthelossofelectrons,andreductioninvolvestheadditionofelectrons.Sinceelectronsareconservedinchemicalreactions,oxidationmustbecoupledwithreduction(redoxreactions).,1.Electron-transportchain(4),Theoxidation-reductionpotential(redoxpotential)ofacompoundisameasureofitsaffinityforelectrons.Redoxpotentialsaremeasuredrelativetohydrogen;thus,apositiveredoxpotentialindicatesthatthecompoundhasagreateraffinityforelectronsthanhashydrogenandwouldacceptelectronsfromhydrogen.Anegativeredoxpotentialindicatesaloweraffinityandthusthemoleculewoulddonateelectronstohydrogen.,1.Electron-transportchain(5),ThedifferenceinredoxpotentialbetweenNADH+H+/NAD+(-0.32V)andO2/H2O(+0.82V)drivesthemovementofelectronsthroughaseriesofelectroncarrierswhicharearrangedtoacceptelectronsfromacarrierwithamorenegativeredoxpotentialanddonatetothenextcarrierwhichhasamorepositiveredoxpotential.Energyisreleasedastheelectronsmovebetweencarriers.IftheenergyreleaseislargethiscanbecoupledwiththemovementofH+acrossthemembrane,whichcangenerateATP.Thenumberofsiteswherethiscanoccurdependsonthedifferencebetweentheredoxpotentialofthesubstrateandthefinalelectronacceptor.,1.Electron-transportchain(6),ThechemiosmotichypothesisisawidelyacceptedtheorythatexplainshowthemovementofprotonsislinkedtotheformationofATP.Accordingtothishypothesistheelectron-transportpathwayisorganizedsuchthatwhenelectronsmovethroughthechain,protonsaretransferredfromonesideofthemembranetotheotherviaaseriesofpumps.WhenNADH+H4istheelectrondonorandoxygenistheterminalelectronacceptor,protonmovementoccursatthreesites,whichareassociatedwithlargefreeenergychanges.ThesitesareNADHdehydrogenase,cytochromebe,complexandtheterminaloxidase.,2.FormationofATP,Inmicrobeswithshortpathwaysorwhereelectronsenteratothersitesinthechain(andhaveamorepositiveredoxpotentialthanthatoftheDH+H+/NAD+couple)lessATPisproduced.ThepumpingofH+acrossthemembraneproducesaprotonmotiveforce(PMF),whichisproducedasaresultoftheunevendistributionofH+acrossthemembrane(themembraneactsasabarrierasitisimpermeabletoH+).WhenH+aretransportedbackintothecellenergyisreleasedandthisdrivesthesynthesisofATP.ThisprocessiscatalyzedbyATPsynthase(ATPase)whichallowsH4tomovethroughthemembrane,andtheenergyreleasediscoupledwithATPsynthesis.PMFcanbeuseddirectlytodrivesomeprocessessuchasactivetransportandrotationofbacterialflagella.,2.FormatiionofATP(2),TransferandreceiveofthehydrogenThepotentialchemicalenergystoredintheorganicmoleculessuchasGisreleasedbythetransferringofHproducedthroughfourpathwayswediscussedabovetothehydrogenreceptor.Onthebasisoftheattributesofhydrogenreceptor,biologicaloxidationcanbeclassifiedasthefollowingthreetypes:1.Respiration2.Anearobicrespiration3.fermentation,Transferandreceive,Respirationa.k.a.Aerobicrespirationisthemostuniversalandthemostimportantbiologicaloxidationorenergy-yieldingway,theHremovedfromthesubstratethroughconventionalchannelsweretransportedviafullyrespiratorychain,thatis,electrontransportchain(ETC),andfinallywereacceptedbytheextraneousoxygenmolecules,simultaneouslyreleasingenergyandwater.Itsahigh-efficientenergy-yieldingstylewhichtransferingandreceptionofHinthepresenceofoxygen.,1.respiration,2.Anaerobicrespiration,Theterminalhydrogenreceptorofanaerobicrespirationisextraneousinorganic(onlyafewareorganic)oxidativecompounds(无机氧化物),.Itsaspecialrespiratorywithratherlowenergy-yieldingefficiencyintheabsenceofoxygen.TheHistransportedbypartialETC,itcanbedividedintomanytypesonthebasesoftheterminalHreceptor.,A.NitraterespirationB.SulfaterespirationC.SulferrespirationD.IronrespirationE.CarbonaterespirationF.Fumaraterespiration(延胡索酸呼吸),Typesofanaerobicrespiration,Nitraterespiration(denitrification)(硝酸盐呼吸又称反硝化作用),Assimilativenitratereductioninthepresenceorabsenceofoxygen(同化型硝酸盐还原作用)Dissimilativenitratereductionanearobically(异化型硝酸盐还原作用)nitrateNO,N2O,orevenN2,Manymicrobesliveinenvironmentsdevoidofoxygen.Toutilizeelectron-transportmechanismsforATPsynthesis,alternativeinorganicelectronacceptorssuchasnitrate,sulfateandCO2areusedinsteadofoxygen.Thoseorganismsthatarefacultative(兼性微生物)willuseoxygenforaerobicrespirationwhenavailable.Microbesthatusenitrate(硝酸盐)asanelectronacceptorreducenitratetonitrite(亚硝酸盐)andammoniabytheactionofnitrateandnitritereductase:NO3-+NADPH+H+NO2-+NADP+H2ONO2-NH2OHNH3,3.Anaerobicrespiration,ThisisalargelyinefficientmethodfortheproductionofATP;thus,alargeamountofnitrateisrequiredtoproducesufficientATPforthecell.NitritecanalsobereducedtoN2byamoreefficientmechanism.Thisprocessisknownasdenitrification(反硝化作用)andisperformedbyPseudomonasandsomeBacillusspecies:2N03-+lOe-+12H+N2+6H2O,Othergroupsthatusealternativeelectronacceptorsincludemethanogens(产甲烷菌),whichareobligateanaerobesandreduceCO2orcarbonate(碳酸盐)tomethane(methanogenesis):HCO3-+H+4H2CH4+3H20andthosethatcanreducesulfate(硫酸盐)tosulfide(硫化物)(Desulfovibrio脱硫弧菌):S042-+8e-+8H+S2-+4H2OAnaerobicrespirationismuchlessefficientthanaerobicrespiration;however,theyieldofATPbythismechanismismuchgreaterthanthatobtainedbyfermentationalone.(无氧呼吸比有氧呼吸产能效率更低;然而,通过无氧呼吸这个机制,ATP产率比单独发酵却大得多),AmajorproductinthecatabolicpathwaysdescribedpreviouslyisNADH+H+Inthepresenceofoxygenthiscanbeoxidizedbytheelectron-transportpathway.However,intheabsenceofoxygen,thismustbeoxidizedbacktoNAD+.Manymi