微生物吸收营养物质的方式单纯扩散PPT课件

.,1,微生物吸收营养物质的方式,.,2,1、单纯扩散(simplediffusionorpassivediffusion),被输送的物质，靠细胞内外浓度为动力，以透析或扩散的形式从高浓度区向低浓度区的扩散。,Simplediffusionmeansthatthemoleculescanpassdirectlythroughthemembrane.Diffusionisalwaysdownaconcentrationgradient.Thislimitsthemaximumpossibleconcentrationofthemoleculeinsidethecell(oroutsidethecellifitisawasteproduct).Theeffectivenessofdiffusionisalsolimitedbythediffusionrateofthemolecule.Therefore,thoughdiffusionisaneffectiveenoughtransportmechanismforsomesubstances(suchasH2O),thecellmustutilizeothermechanismsformanyofitstransportneeds.,.,3,1、单纯扩散(simplediffusionorpassivediffusion),特点：扩散是非特异性的营养物质吸收方式：如营养物质通过细胞膜中的含水小孔，由高浓度的胞外环境向低浓度的胞内扩散；在扩散过程中营养物质的结构不发生变化：即既不与膜上的分子发生反应，本身的分子结构也不发生变化；物质运输的速率较慢：速率与胞内外营养物质的浓度差有关，即随细胞膜内外该物质浓度差的降低而减小，直到胞内外物质浓度相同；不需要载体参与；扩散是一个不需要代谢能的运输方式：因此，物质不能进行逆浓度运输。可运送的养料有限：限于水、溶于水的气体，及分子量小，脂溶性、极性小的营养物质。,.,4,smosis,flowstowardshighsaltconcentrations,.,5,单纯扩散模式图,细胞膜外,细胞膜内,细胞膜,.,6,三营养物通过与细胞膜上载体蛋白（也称作透过酶permease）的可逆性结合来加快其传递速度,促进扩散(facilitateddiffusion/transport),Facilitateddiffusionutilizesmembraneproteinchannelstoallowchargedmolecules(whichotherwisecouldnotdiffuseacrossthecellmembrane)tofreelydiffuseinandoutofthecell.ThesechannelscomesintogreatestusewithsmallionslikeK+,Na+,andCl-.Thespeedoffacilitatedtransportislimitedbythenumberofproteinchannelsavailable,whereasthespeedofdiffusionisdependentonlyontheconcentrationgradient.,.,7,促进扩散(facilitateddiffusion),特点：在促进扩散过程中营养物质本身在分子结构上也不会发生变化不消耗代谢能量，故不能进行逆浓度运输运输的速率由胞内外该物质的浓度差决定需要细胞膜上的载体蛋白（透过酶）参与物质运输被运输的物质与载体蛋白有高度的特异性养料浓度过高时,与载体蛋白出现饱和效应促进扩散的运输方式多见于真核微生物中，例如通常在厌氧生活的酵母菌中，某些物质的吸收和代谢产物的分泌是通过这种方式完成的。,.,8,Embededprotein:,.,9,.,10,Proteinsthatactascarriersaretoolargetomoveacrossthemembrane.Theyaretransmembraneproteins.Theycyclebetweentwoconformationsinwhichasolutebindingsiteisaccessibleononesideofthemembraneortheother.,.,11,.,12,oractiveansport,.,13,主动运输(Activetransport),在代谢能的推动下，通过膜上特殊载体蛋白逆养料浓度梯度吸收营养物质的过程,.,14,主动运输(Activetransport),特点：物质在主动运输的过程中需要消耗代谢能可以进行逆浓度运输的运输方式需要载体蛋白参与对被运输的物质有高度的立体专一性被运输的物质在转移的过程中不发生任何化学变化不同的微生物在主动运输过程中所需的能量的来源不同，好氧微生物中直接来自呼吸能，厌氧微生物主要来自化学能，光合微生物中则主要来自光能。主动运输是微生物吸收营养物质的主要方式。,.,15,Comparisonofpassiveandactivetransport.,Legend:Ifunchargedsolutesaresmallenough,theycanmovedowntheirconcentrationgradientsdirectlyacrossthelipidbilayeritselfbysimplediffusion.Examplesofsuchsolutesareethanol,carbondioxide,andoxygen.Mostsolutes,however,cancrossthemembraneonlyifthereisamembranetransportprotein(acarrierproteinorachannelprotein)totransferthem.Asindicated,passivetransport,inthesamedirectionasaconcentrationgradient,occursspontaneously,whereastransportagainstaconcentrationgradient(activetransport)requiresaninputofenergy.Onlycarrierproteinscancarryoutactivetransport,butbothcarrierproteinsandchannelproteinscancarryoutpassivetransport.,.,16,.,17,主动运输模式图,细胞膜,细胞膜外,细胞膜内,恢复原构象,移位,再循环,结合,构象改变,.,18,Na+-K+-ATP酶系统,Na+-K+-ATPase是存在于原生质膜上的一种重要离子通道蛋白功能:利用ATP能量将Na+由细胞内“泵”出胞外,并将K+“泵”入胞内。该酶由大小两个亚基组成（MW:12万,5.5万）,.,19,作用步骤:1.ATP酶(E)在细胞内侧与3个Na+结合,同时消耗能量;2.磷酸化ATP酶(E+)构象变化将Na+排除胞外,并与2个K+结合;3.K+激发E+脱磷酸化恢复为E,同时将K+运入细胞.,.,20,.,21,基因转位是一种特殊的主动运输，与普通的主动运输相比，营养物质在运输的过程中发生了化学变化（糖在运输的过程中发生了磷酸化）。其余特点与主动运输相同。基因转位主要存在于厌氧和兼性厌氧型细菌中，也主要是用于单（或双）糖与糖的衍生物，以及核苷与脂肪散的运输,基团转位(Grouptranslocation),.,22,在酶的作用下HPr被激活,在酶的作用下P-HPr将磷酸转移给糖,.,23,运送机制:是依靠磷酸转移酶系统,即磷酸烯醇式丙酮酸-己糖磷酸转移酶系统.运送步骤:1.热稳载体蛋白(HPr)的激活细胞内高能化合物磷酸烯醇式丙酮酸（PEP）的磷酸基团把HPr激活。酶1PEP+HPr丙酮酸+P-HPrHPr是一种低分子量的可溶性蛋白，结合在细胞膜上，具有高能磷酸载体的作用。,.,24,2、糖被磷酸化后运入膜内膜外环境中的糖先与外膜表面的酶2结合，再被转运到内膜表面。这时，糖被P-HPr上的磷酸激活，并通过酶2的作用将糖-磷酸释放到细胞内。酶2P-HPr+糖糖-P+HPr酶2是一种结合于细胞膜上的蛋白，它对底物具有特异性选择作用，因此细胞膜上可诱导出一系列与底物分子相应的酶2。,.,25,.,26,四种运输营养物质方式的比较,.,27,SpecialCases1.Endocytosis2.Exocytosis,.,28,Therearefourtypesofcarrier-mediatedtransportsystemsinprocaryotes.Thecarrierisaprotein(orgroupofproteins)thatfunctioninthepassageofasmallmoleculefromonesideofamembranetoanother.Atransportsystemmaybeasingletransmembranousproteinthatformsachannelthatadmitspassageofaspecificsolute.Oratransportsystemmaybeacoordinatedsystemofproteinsthatbindsandsequentiallypassesasmallmoleculethroughmembrane.Transportsystemshavethepropertyofspecificityforthesolutetransported.Sometransportsystemstransportasinglesolutewiththesamespecificityandkineticsasanenzyme.Sometransportsystemswilltransport(structurally)relatedmolecules,althoughatreducedefficiencycomparedtotheirprimarysubstrate.Mosttransportsystemstransportspecificsugars,aminoacids,anionsorcationsthatareofnutritionalvaluetothebacterium.,.,29,Figure12.Transportprocessesinbacterialcells.Solutesenterorexitfrombacterialcellsbymeansofoneofthreeprocesses:uniport,symport(alsocalledcotransport)andantiport(alsocalledexchangediffusion).Transportsystems(Figure13below)operatebyoneoranotheroftheseprocesses.,.,30,.,31,Facilitateddiffusionsystems(FD)aretheleastcommontypeoftransportsysteminbacteria.Actually,theglyceroluniporterinE.coliistheonlywellknownfacilitateddiffusionsystem.FDinvolvesthepassageofaspecificsolutethroughacarrierthatformsachannelinthemembrane.Thesolutecanmoveineitherdirectionthroughthemembranetothepointofofequilibriumonbothsidesofthemembrane.Althoughthesystemiscarrier-mediatedandspecific,noenergyisexpendedinthetransportprocess.Forthisreasontheglycerolmoleculecannotbeaccumulatedagainsttheconcentrationgradient.,Facilitateddiffusionsystems(FD),.,32,Iondriventransportsystems(IDT)andBinding-proteindependenttransportsystems(BPDT)areactivetransportsystemsthatareusedfortransportofmostsolutesbybacterialcells.IDTisusedforaccumulationofmanyionsandaminoacids;BPDTisfrequentlyusedforsugarsandaminoacids.IDTisasymportorantiportprocessthatusesahydrogenion(H+)i.e.,protonmotiveforce(pmf),orsomeothercation,i.e.,chemiosmoticpotential,todrivethetransportprocess.IDTsystemssuchasthelactosepermeaseofE.coliutilizetheconsumptionofahydrogenionduringthetransportoflactose.Thustheenergyexpendedduringactivetransportoflactoseisintheformofpmf.Thelactosepermeaseisasingletransmembranouspolypeptidethatspansthemembraneseventimesformingachannelthatspecificallyadmitslactose.,.,33,Binding-proteindependenttransportsystems,suchasthehistadinetransportsysteminE.coli,arecomposedoffourproteins.Twoproteinsformamembranechannelthatallowspassageofthehistadine.Athirdproteinresidesintheperiplasmicspacewhereitisabletobindtheaminoacidandpassittoaforthproteinwhichadmitstheaminoacidintothemembranechannel.Drivingthesolutethroughthechannelinvolvestheexpenditureofenergy,whichisprovidedbythehydrolysisofATP.,.,34,Grouptranslocationsystems(GT),morecommonlyknownasthephosphotransferasesystem(PTS)inE.coli,areusedprimarilyforthetransportofsugars.Likebindingprotein-dependenttransportsystems,theyarecomposedofseveraldistinctcomponents.However,GTsystemsspecificforonesugarmaysharesomeoftheircomponentswithothergrouptransportsystems.InE.coli,glucosemaybetransportedbyagrouptranslocationprocessthatinvolvesthephosphotransferasesystem.Theactualcarrierinthem