细胞质膜结构和膜上运输.ppt

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1、细胞质膜结构和膜上运输PlasmaMembraneStructureandFunctionTheplasmamembraneseparatestheinternalenvironmentofthecellfromitssurroundings.Theplasmamembraneisaphospholipidbilayerwithembeddedproteins.Theplasmamembranehasafluidconsistencyandamosaicpatternofembeddedprotei

2、ns.Fluid-mosaicmodelofmembranestructureCellsliveinfluidenvironments,withwaterinsideandoutsidethecell.Hydrophilic(water-loving)polarheadsofthephospholipidmoleculeslieontheoutward-facingsurfacesoftheplasmamembrane.Hydrophobic(water-fearing)nonpolartailse

3、xtendtotheinterioroftheplasmamembrane.Plasmamembraneproteinsmaybeperipheralproteinsorintegralproteins.Asidefromphospholipid,cholesterolisanotherlipidinanimalplasmamembranes;relatedsteroidsarefoundinplants.Cholesterolstrengthenstheplasmamembrane.Whenpho

4、spholipidshavecarbohydratechainsattached,theyarecalledglycolipids.Whenproteinshavecarbohydratechainsattached,theyarecalledglycoproteins.Carbohydratechainsoccuronlyontheexteriorsurfaceoftheplasmamembrane.Theoutsideandinsidesurfacesoftheplasmamembraneare

5、notidentical.ChannelproteinCarrierproteinCellrecognitionproteinInanimalcells,thecarbohydratechainsofcellrecognitionproteinsarecollectivelycalledtheglycocalyx.Theglycocalyxcanfunctionincell-to-cellrecognition,adhesionbetweencells,andreceptionofsignalmol

6、ecules.Thediversityofcarbohydratechainsisenormous,providingeachindividualwithauniquecellular“fingerprint”.ReceptorproteinEnzymaticproteinThePermeabilityofthePlasmaMembraneTheplasmamembraneisdifferentiallypermeable.Macromoleculescannotpassthroughbecause

7、ofsize,andtinychargedmoleculesdonotpassthroughthenonpolarinteriorofthemembrane.Small,unchargedmoleculespassthroughthemembrane,followingtheirconcentrationgradient.HowmoleculescrosstheplasmamembraneMovementofmaterialsacrossamembranemaybepassiveoractive.P

8、assivetransportdoesnotusechemicalenergy;diffusionandfacilitatedtransportarebothpassive.Activetransportrequireschemicalenergyandusuallyacarrierprotein.Exocytosisandendocytosistransportmacromoleculesacrossplasmamembranesusingvesicleformat