《生物化学第十一章》PPT课件

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1、Ediden,M.(2003)Nat.Rev.Mol.CellBiol.4:414-4185.Membranetransport:Proteinscanfacilitateordrivethetransportofspecificmoleculesacrossamembranebarrier-PassivetransportDiffusionFacilitatedtransport-ActivetransportEnergy-coupledsystemATPpoweredtransportConcentrationgradientClass

2、ificationoftransportersTransportersCarriesChannels23UniportersSecondaryactivetransportersPrimaryactivetransporters1Whatisthedifferencebetweencarrierandchannel?TheTransporterClassificationSystem1.A.aHelixtypechannelsvoltage-gatedK+channelaquaporinsacetylcholinereceptor/chan

3、nel1.B.bBarrelporinsgeneralbacterialporin(GBP)family1.C.Pore-formingtoxins2.A.Porters:uniporters,symporters,andantiporters2.B.Nonribosomallysynthesizedporters:valinomycin3.A.Diphosphatebondhydrolysis-driventransporters(usePPi,notATP):ATP-bindingcassette(ABC)superfamilyP-ty

4、peATPasesuperfamilyF-,V-andA-typeATPasesuperfamilyConcentrationGradientsTheconc.gradientisthedifferenceinconc.betweeneachcompartment(C2-C1)Thechemicalpotentialdifference(G)foramoleculediffusingfromonesidewithC1totheotherwithC2definedbytheratiooftheconcentrationsG=RTlnC2/

5、C1ChargeGradientsInadditiontoconc.gradient,adifferenceinchargecanleadtoelectrostaticattractionthatmaydrivediffusionZ=chargeonmoleculebeingdiffusedF=Faradayconstant(96,485JV-1mole-1)=voltagedifference(electricpotential)G=RTlnC2/C1+ZFPassiveDiffusionPassivediffusionisaf

6、irstorderkineticprocessandratedependsdirectlyonconcentration.FacilitateddiffusionisassistedbyproteinsanddisplaysMichaelis-MentenreactionkineticsPassiveFacilitatedA(outside)A(inside)V0=k[A]0kA(outside)+MP(membraneprotein)A(MP)A(inside)+MPkV0=Vmax[A]0/(Kt+[A]0)Atransporterpr

7、oteinreducestheG‡fortransmembranediffusionofthesolute:byformingnon-covalentinteractionswiththehydratedsoluteprovidingahydrophilictransmembranepassagewayAquaporinsformhydrophilictransmembranechannelsforthepassageofwaterWatermoleculesflowthroughanAPQ-1channelattherateof109s

8、-1.Thelowactivationenergyforpassageofwaterthroughaquaporinchannel(DG<15kJ/mol)isrequired.