Cell membrane - Wikipedia

文章推薦指數: 80 %
投票人數:10人

The cell membrane is a biological membrane that separates the interior of all cells from the outside environment (the extracellular space) which protects ... Cellmembrane FromWikipedia,thefreeencyclopedia Jumptonavigation Jumptosearch Biologicalmembranethatseparatestheinteriorofacellfromitsoutsideenvironment IllustrationofaEukaryoticcellmembrane ComparisonofEukaryotesvs.Prokaryotes Thecellmembrane(alsoknownastheplasmamembrane(PM)orcytoplasmicmembrane,andhistoricallyreferredtoastheplasmalemma)isabiologicalmembranethatseparatestheinteriorofallcellsfromtheoutsideenvironment(theextracellularspace)whichprotectsthecellfromitsenvironment.[1][2]Thecellmembraneconsistsofalipidbilayer,includingcholesterols(alipidcomponent)thatsitbetweenphospholipidstomaintaintheirfluidityatvarioustemperatures.Themembranealsocontainsmembraneproteins,includingintegralproteinsthatgoacrossthemembraneservingasmembranetransporters,andperipheralproteinsthatlooselyattachtotheouter(peripheral)sideofthecellmembrane,actingasenzymesshapingthecell.[3]Thecellmembranecontrolsthemovementofsubstancesinandoutofcellsandorganelles.Inthisway,itisselectivelypermeabletoionsandorganicmolecules.[4]Inaddition,cellmembranesareinvolvedinavarietyofcellularprocessessuchascelladhesion,ionconductivityandcellsignallingandserveastheattachmentsurfaceforseveralextracellularstructures,includingthecellwall,thecarbohydratelayercalledtheglycocalyx,andtheintracellularnetworkofproteinfiberscalledthecytoskeleton.Inthefieldofsyntheticbiology,cellmembranescanbeartificiallyreassembled.[5][6][7][8] Contents 1History 2Composition 2.1Lipids 2.2Phospholipidsforminglipidvesicles 2.3Carbohydrates 2.4Proteins 3Function 4Prokaryotes 5Structures 5.1Fluidmosaicmodel 5.2Lipidbilayer 5.3Membranepolarity 5.4Membranestructures 5.5Cytoskeleton 5.6Intracellularmembranes 5.7Variations 6Permeability 7Seealso 8Notesandreferences 9Externallinks History Mainarticle:HistoryofcellmembranetheoryWhileRobertHooke’sdiscoveryofcellsin1665ledtotheproposaloftheCellTheory,Hookemisledthecellmembranetheorythatallcellscontainedahardcellwallsinceonlyplantcellscouldbeobservedatthetime.[9]Microscopistsfocusedonthecellwallforwellover150yearsuntiladvancesinmicroscopyweremade.Intheearly19thcentury,cellswererecognizedasbeingseparateentities,unconnected,andboundbyindividualcellwallsafteritwasfoundthatplantcellscouldbeseparated.Thistheoryextendedtoincludeanimalcellstosuggestauniversalmechanismforcellprotectionanddevelopment.Bythesecondhalfofthe19thcentury,microscopywasstillnotadvancedenoughtomakeadistinctionbetweencellmembranesandcellwalls.However,somemicroscopistscorrectlyidentifiedatthistimethatwhileinvisible,itcouldbeinferredthatcellmembranesexistedinanimalcellsduetointracellularmovementofcomponentsinternallybutnotexternallyandthatmembraneswerenottheequivalentofacellwalltoplantcell.Itwasalsoinferredthatcellmembraneswerenotvitalcomponentstoallcells.Manyrefutedtheexistenceofacellmembranestilltowardstheendofthe19thcentury.In1890,anupdatetotheCellTheorystatedthatcellmembranesexisted,butweremerelysecondarystructures.Itwasnotuntillaterstudieswithosmosisandpermeabilitythatcellmembranesgainedmorerecognition.[9]In1895,ErnestOvertonproposedthatcellmembranesweremadeoflipids.[10] Thelipidbilayerhypothesis,proposedin1925byGorterandGrendel,[11]createdspeculationtothedescriptionofthecellmembranebilayerstructurebasedoncrystallographicstudiesandsoapbubbleobservations.Inanattempttoacceptorrejectthehypothesis,researchersmeasuredmembranethickness.[9]In1925itwasdeterminedbyFrickethatthethicknessoferythrocyteandyeastcellmembranesrangedbetween3.3and4 nm,athicknesscompatiblewithalipidmonolayer.Thechoiceofthedielectricconstantusedinthesestudieswascalledintoquestionbutfuturetestscouldnotdisprovetheresultsoftheinitialexperiment.Independently,theleptoscopewasinventedinordertomeasureverythinmembranesbycomparingtheintensityoflightreflectedfromasampletotheintensityofamembranestandardofknownthickness.TheinstrumentcouldresolvethicknessesthatdependedonpHmeasurementsandthepresenceofmembraneproteinsthatrangedfrom8.6to23.2 nm,withthelowermeasurementssupportingthelipidbilayerhypothesis.Laterinthe1930s,themembranestructuremodeldevelopedingeneralagreementtobethepaucimolecularmodelofDavsonandDanielli(1935).Thismodelwasbasedonstudiesofsurfacetensionbetweenoilsandechinodermeggs.Sincethesurfacetensionvaluesappearedtobemuchlowerthanwouldbeexpectedforanoil–waterinterface,itwasassumedthatsomesubstancewasresponsibleforloweringtheinterfacialtensionsinthesurfaceofcells.Itwassuggestedthatalipidbilayerwasinbetweentwothinproteinlayers.Thepaucimolecularmodelimmediatelybecamepopularanditdominatedcellmembranestudiesforthefollowing30years,untilitbecamerivaledbythefluidmosaicmodelofSingerandNicolson(1972).[12][9] Despitethenumerousmodelsofthecellmembraneproposedpriortothefluidmosaicmodel,itremainstheprimaryarchetypeforthecellmembranelongafteritsinceptioninthe1970s.[9]Althoughthefluidmosaicmodelhasbeenmodernizedtodetailcontemporarydiscoveries,thebasicshaveremainedconstant:themembraneisalipidbilayercomposedofhydrophilicexteriorheadsandahydrophobicinteriorwhereproteinscaninteractwithhydrophilicheadsthroughpolarinteractions,butproteinsthatspanthebilayerfullyorpartiallyhavehydrophobicaminoacidsthatinteractwiththenon-polarlipidinterior.Thefluidmosaicmodelnotonlyprovidedanaccuraterepresentationofmembranemechanics,itenhancedthestudyofhydrophobicforces,whichwouldlaterdevelopintoanessentialdescriptivelimitationtodescribebiologicalmacromolecules.[9] Formanycenturies,thescientistsciteddisagreedwiththesignificanceofthestructuretheywereseeingasthecellmembrane.Foralmosttwocenturies,themembraneswereseenbutmostlydisregardedthisasanimportantstructurewithcellularfunction.Itwasnotuntilthe20thcenturythatthesignificanceofthecellmembraneasitwasacknowledged.Finally,twoscientistsGorterandGrendel(1925)madethediscoverythatthemembraneis“lipid-based”.Fromthis,theyfurtheredtheideathatthisstructurewouldhavetobeinaformationthatmimickedlayers.Oncestudiedfurther,itwasfoundbycomparingthesumofthecellsurfacesandthesurfacesofthelipids,a2:1ratiowasestimated;thus,providingthefirstbasisofthebilayerstructureknowntoday.Thisdiscoveryinitiatedmanynewstudiesthatarosegloballywithinvariousfieldsofscientificstudies,confirmingthatthestructureandfunctionsofthecellmembranearewidelyaccepted.[9] Thestructurehasbeenvariouslyreferredtobydifferentwritersastheectoplast(deVries,1885),[13]Plasmahaut(plasmaskin,Pfeffer,1877,1891),[14]Hautschicht(skinlayer,Pfeffer,1886;usedwithadifferentmeaningbyHofmeister,1867),plasmaticmembrane(Pfeffer,1900),[15]plasmamembrane,cytoplasmicmembrane,cellenvelopeandcellmembrane.[16][17]Someauthorswhodidnotbelievethattherewasafunctionalpermeableboundaryatthesurfaceofthecellpreferredtousethetermplasmalemma(coinedbyMast,1924)fortheexternalregionofthecell.[18][19][20] Composition Cellmembranescontainavarietyofbiologicalmolecules,notablylipidsandproteins.Compositionisnotset,butconstantlychangingforfluidityandchangesintheenvironment,evenfluctuatingduringdifferentstagesofcelldevelopment.Specifically,theamountofcholesterolinhumanprimaryneuroncellmembranechanges,andthischangeincompositionaffectsfluiditythroughoutdevelopmentstages.[21] Materialisincorporatedintothemembrane,ordeletedfromit,byavarietyofmechanisms: Fusionofintracellularvesicleswiththemembrane(exocytosis)notonlyexcretesthecontentsofthevesiclebutalsoincorporatesthevesiclemembrane'scomponentsintothecellmembrane.Themembranemayformblebsaroundextracellularmaterialthatpinchofftobecomevesicles(endocytosis). Ifamembraneiscontinuouswithatubularstructuremadeofmembranematerial,thenmaterialfromthetubecanbedrawnintothemembranecontinuously. Althoughtheconcentrationofmembranecomponentsintheaqueousphaseislow(stablemembranecomponentshavelowsolubilityinwater),thereisanexchangeofmoleculesbetweenthelipidandaqueousphases. Lipids Examplesofthemajormembranephospholipidsandglycolipids:phosphatidylcholine(PtdCho),phosphatidylethanolamine(PtdEtn),phosphatidylinositol(PtdIns),phosphatidylserine(PtdSer).Thecellmembraneconsistsofthreeclassesofamphipathiclipids:phospholipids,glycolipids,andsterols.Theamountofeachdependsuponthetypeofcell,butinthemajorityofcasesphospholipidsarethemostabundant,oftencontributingforover50%ofalllipidsinplasmamembranes.[22][23]Glycolipidsonlyaccountforaminuteamountofabout2%andsterolsmakeuptherest.InRBCstudies,30%oftheplasmamembraneislipid.However,forthemajorityofeukaryoticcells,thecompositionofplasmamembranesisabouthalflipidsandhalfproteinsbyweight. Thefattychainsinphospholipidsandglycolipidsusuallycontainanevennumberofcarbonatoms,typicallybetween16and20.The16-and18-carbonfattyacidsarethemostcommon.Fattyacidsmaybesaturatedorunsaturated,withtheconfigurationofthedoublebondsnearlyalways"cis".Thelengthandthedegreeofunsaturationoffattyacidchainshaveaprofoundeffectonmembranefluidityasunsaturatedlipidscreateakink,preventingthefattyacidsfrompackingtogetherastightly,thusdecreasingthemeltingtemperature(increasingthefluidity)ofthemembrane.[22][23]Theabilityofsomeorganismstoregulatethefluidityoftheircellmembranesbyalteringlipidcompositioniscalledhomeoviscousadaptation. Theentiremembraneisheldtogethervianon-covalentinteractionofhydrophobictails,howeverthestructureisquitefluidandnotfixedrigidlyinplace.Underphysiologicalconditionsphospholipidmoleculesinthecellmembraneareintheliquidcrystallinestate.Itmeansthelipidmoleculesarefreetodiffuseandexhibitrapidlateraldiffusionalongthelayerinwhichtheyarepresent.[22]However,theexchangeofphospholipidmoleculesbetweenintracellularandextracellularleafletsofthebilayerisaveryslowprocess.Lipidraftsandcaveolaeareexamplesofcholesterol-enrichedmicrodomainsinthecellmembrane.[23]Also,afractionofthelipidindirectcontactwithintegralmembraneproteins,whichistightlyboundtotheproteinsurfaceiscalledannularlipidshell;itbehavesasapartofproteincomplex. Inanimalcellscholesterolisnormallyfounddispersedinvaryingdegreesthroughoutcellmembranes,intheirregularspacesbetweenthehydrophobictailsofthemembranelipids,whereitconfersastiffeningandstrengtheningeffectonthemembrane.[4]Additionally,theamountofcholesterolinbiologicalmembranesvariesbetweenorganisms,celltypes,andeveninindividualcells.Cholesterol,amajorcomponentofanimalplasmamembranes,regulatesthefluidityoftheoverallmembrane,meaningthatcholesterolcontrolstheamountofmovementofthevariouscellmembranecomponentsbasedonitsconcentrations.[4]Inhightemperatures,cholesterolinhibitsthemovementofphospholipidfattyacidchains,causingareducedpermeabilitytosmallmoleculesandreducedmembranefluidity.Theoppositeistruefortheroleofcholesterolincoolertemperatures.Cholesterolproduction,andthusconcentration,isup-regulated(increased)inresponsetocoldtemperature.Atcoldtemperatures,cholesterolinterfereswithfattyacidchaininteractions.Actingasantifreeze,cholesterolmaintainsthefluidityofthemembrane.Cholesterolismoreabundantincold-weatheranimalsthanwarm-weatheranimals.Inplants,whichlackcholesterol,relatedcompoundscalledsterolsperformthesamefunctionascholesterol.[4] Phospholipidsforminglipidvesicles Lipidvesiclesorliposomesareapproximatelysphericalpocketsthatareenclosedbyalipidbilayer.[24]Thesestructuresareusedinlaboratoriestostudytheeffectsofchemicalsincellsbydeliveringthesechemicalsdirectlytothecell,aswellasgettingmoreinsightintocellmembranepermeability.Lipidvesiclesandliposomesareformedbyfirstsuspendingalipidinanaqueoussolutionthenagitatingthemixturethroughsonication,resultinginavesicle.Bymeasuringtherateofeffluxfromthatoftheinsideofthevesicletotheambientsolution,allowsresearchertobetterunderstandmembranepermeability.Vesiclescanbeformedwithmoleculesandionsinsidethevesiclebyformingthevesiclewiththedesiredmoleculeorionpresentinthesolution.Proteinscanalsobeembeddedintothemembranethroughsolubilizingthedesiredproteinsinthepresenceofdetergentsandattachingthemtothephospholipidsinwhichtheliposomeisformed.Theseprovideresearcherswithatooltoexaminevariousmembraneproteinfunctions. Carbohydrates Plasmamembranesalsocontaincarbohydrates,predominantlyglycoproteins,butwithsomeglycolipids(cerebrosidesandgangliosides).Carbohydratesareimportantintheroleofcell-cellrecognitionineukaryotes;theyarelocatedonthesurfaceofthecellwheretheyrecognizehostcellsandshareinformation,virusesthatbindtocellsusingthesereceptorscauseaninfection[25]Forthemostpart,noglycosylationoccursonmembraneswithinthecell;rathergenerallyglycosylationoccursontheextracellularsurfaceoftheplasmamembrane.Theglycocalyxisanimportantfeatureinallcells,especiallyepitheliawithmicrovilli.Recentdatasuggesttheglycocalyxparticipatesincelladhesion,lymphocytehoming,[25]andmanyothers.Thepenultimatesugarisgalactoseandtheterminalsugarissialicacid,asthesugarbackboneismodifiedintheGolgiapparatus.Sialicacidcarriesanegativecharge,providinganexternalbarriertochargedparticles. Proteins Type Description Examples Integralproteinsortransmembraneproteins Spanthemembraneandhaveahydrophiliccytosolicdomain,whichinteractswithinternalmolecules,ahydrophobicmembrane-spanningdomainthatanchorsitwithinthecellmembrane,andahydrophilicextracellulardomainthatinteractswithexternalmolecules.Thehydrophobicdomainconsistsofone,multiple,oracombinationofα-helicesandβsheetproteinmotifs. Ionchannels,protonpumps,Gprotein-coupledreceptor Lipidanchoredproteins Covalentlyboundtosingleormultiplelipidmolecules;hydrophobicallyinsertintothecellmembraneandanchortheprotein.Theproteinitselfisnotincontactwiththemembrane. Gproteins Peripheralproteins Attachedtointegralmembraneproteins,orassociatedwithperipheralregionsofthelipidbilayer.Theseproteinstendtohaveonlytemporaryinteractionswithbiologicalmembranes,andoncereacted,themoleculedissociatestocarryonitsworkinthecytoplasm. Someenzymes,somehormones Thecellmembranehaslargecontentofproteins,typicallyaround50%ofmembranevolume[26]Theseproteinsareimportantforthecellbecausetheyareresponsibleforvariousbiologicalactivities.Approximatelyathirdofthegenesinyeastcodespecificallyforthem,andthisnumberisevenhigherinmulticellularorganisms.[24]Membraneproteinsconsistofthreemaintypes:integralproteins,peripheralproteins,andlipid-anchoredproteins.[4] Asshownintheadjacenttable,integralproteinsareamphipathictransmembraneproteins.Examplesofintegralproteinsincludeionchannels,protonpumps,andg-proteincoupledreceptors.Ionchannelsallowinorganicionssuchassodium,potassium,calcium,orchlorinetodiffusedowntheirelectrochemicalgradientacrossthelipidbilayerthroughhydrophilicporesacrossthemembrane.Theelectricalbehaviorofcells(i.e.nervecells)arecontrolledbyionchannels.[4]Protonpumpsareproteinpumpsthatareembeddedinthelipidbilayerthatallowprotonstotravelthroughthemembranebytransferringfromoneaminoacidsidechaintoanother.ProcessessuchaselectrontransportandgeneratingATPuseprotonpumps.[4]AG-proteincoupledreceptorisasinglepolypeptidechainthatcrossesthelipidbilayerseventimesrespondingtosignalmolecules(i.e.hormonesandneurotransmitters).G-proteincoupledreceptorsareusedinprocessessuchascelltocellsignaling,theregulationoftheproductionofcAMP,andtheregulationofionchannels.[4] Thecellmembrane,beingexposedtotheoutsideenvironment,isanimportantsiteofcell–cellcommunication.Assuch,alargevarietyofproteinreceptorsandidentificationproteins,suchasantigens,arepresentonthesurfaceofthemembrane.Functionsofmembraneproteinscanalsoincludecell–cellcontact,surfacerecognition,cytoskeletoncontact,signaling,enzymaticactivity,ortransportingsubstancesacrossthemembrane. Mostmembraneproteinsmustbeinsertedinsomewayintothemembrane.[27]Forthistooccur,anN-terminus"signalsequence"ofaminoacidsdirectsproteinstotheendoplasmicreticulum,whichinsertstheproteinsintoalipidbilayer.Onceinserted,theproteinsarethentransportedtotheirfinaldestinationinvesicles,wherethevesiclefuseswiththetargetmembrane. Function Adetaileddiagramofthecellmembrane Illustrationdepictingcellulardiffusion Thecellmembranesurroundsthecytoplasmoflivingcells,physicallyseparatingtheintracellularcomponentsfromtheextracellularenvironment.Thecellmembranealsoplaysaroleinanchoringthecytoskeletontoprovideshapetothecell,andinattachingtotheextracellularmatrixandothercellstoholdthemtogethertoformtissues.Fungi,bacteria,mostarchaea,andplantsalsohaveacellwall,whichprovidesamechanicalsupporttothecellandprecludesthepassageoflargermolecules. Thecellmembraneisselectivelypermeableandabletoregulatewhatentersandexitsthecell,thusfacilitatingthetransportofmaterialsneededforsurvival.Themovementofsubstancesacrossthemembranecanbeeither"passive",occurringwithouttheinputofcellularenergy,or"active",requiringthecelltoexpendenergyintransportingit.Themembranealsomaintainsthecellpotential.Thecellmembranethusworksasaselectivefilterthatallowsonlycertainthingstocomeinsideorgooutsidethecell.Thecellemploysanumberoftransportmechanismsthatinvolvebiologicalmembranes: 1.Passiveosmosisanddiffusion:Somesubstances(smallmolecules,ions)suchascarbondioxide(CO2)andoxygen(O2),canmoveacrosstheplasmamembranebydiffusion,whichisapassivetransportprocess.Becausethemembraneactsasabarrierforcertainmoleculesandions,theycanoccurindifferentconcentrationsonthetwosidesofthemembrane.Diffusionoccurswhensmallmoleculesandionsmovefreelyfromhighconcentrationtolowconcentrationinordertoequilibratethemembrane.Itisconsideredapassivetransportprocessbecauseitdoesnotrequireenergyandispropelledbytheconcentrationgradientcreatedbyeachsideofthemembrane.[28]Suchaconcentrationgradientacrossasemipermeablemembranesetsupanosmoticflowforthewater.Osmosis,inbiologicalsystemsinvolvesasolvent,movingthroughasemipermeablemembranesimilarlytopassivediffusionasthesolventstillmoveswiththeconcentrationgradientandrequiresnoenergy.Whilewateristhemostcommonsolventincell,itcanalsobeotherliquidsaswellassupercriticalliquidsandgases.[29] 2.Transmembraneproteinchannelsandtransporters:Transmembraneproteinsextendthroughthelipidbilayerofthemembranes;theyfunctiononbothsidesofthemembranetotransportmoleculesacrossit.[30]Nutrients,suchassugarsoraminoacids,mustenterthecell,andcertainproductsofmetabolismmustleavethecell.Suchmoleculescandiffusepassivelythroughproteinchannelssuchasaquaporinsinfacilitateddiffusionorarepumpedacrossthemembranebytransmembranetransporters.Proteinchannelproteins,alsocalledpermeases,areusuallyquitespecific,andtheyonlyrecognizeandtransportalimitedvarietyofchemicalsubstances,oftenlimitedtoasinglesubstance.Anotherexampleofatransmembraneproteinisacell-surfacereceptor,whichallowcellsignalingmoleculestocommunicatebetweencells.[30] 3.Endocytosis:Endocytosisistheprocessinwhichcellsabsorbmoleculesbyengulfingthem.Theplasmamembranecreatesasmalldeformationinward,calledaninvagination,inwhichthesubstancetobetransportediscaptured.Thisinvaginationiscausedbyproteinsontheoutsideonthecellmembrane,actingasreceptorsandclusteringintodepressionsthateventuallypromoteaccumulationofmoreproteinsandlipidsonthecytosolicsideofthemembrane.[31]Thedeformationthenpinchesofffromthemembraneontheinsideofthecell,creatingavesiclecontainingthecapturedsubstance.Endocytosisisapathwayforinternalizingsolidparticles("celleating"orphagocytosis),smallmoleculesandions("celldrinking"orpinocytosis),andmacromolecules.Endocytosisrequiresenergyandisthusaformofactivetransport. 4.Exocytosis:Justasmaterialcanbebroughtintothecellbyinvaginationandformationofavesicle,themembraneofavesiclecanbefusedwiththeplasmamembrane,extrudingitscontentstothesurroundingmedium.Thisistheprocessofexocytosis.Exocytosisoccursinvariouscellstoremoveundigestedresiduesofsubstancesbroughtinbyendocytosis,tosecretesubstancessuchashormonesandenzymes,andtotransportasubstancecompletelyacrossacellularbarrier.Intheprocessofexocytosis,theundigestedwaste-containingfoodvacuoleorthesecretoryvesiclebuddedfromGolgiapparatus,isfirstmovedbycytoskeletonfromtheinteriorofthecelltothesurface.Thevesiclemembranecomesincontactwiththeplasmamembrane.Thelipidmoleculesofthetwobilayersrearrangethemselvesandthetwomembranesare,thus,fused.Apassageisformedinthefusedmembraneandthevesiclesdischargesitscontentsoutsidethecell. Prokaryotes Prokaryotesaredividedintotwodifferentgroups,ArchaeaandBacteria,withbacteriadividingfurtherintogram-positiveandgram-negative.Gram-negativebacteriahavebothaplasmamembraneandanoutermembraneseparatedbyperiplasm,however,otherprokaryoteshaveonlyaplasmamembrane.Thesetwomembranesdifferinmanyaspects.Theoutermembraneofthegram-negativebacteriadifferfromotherprokaryotesduetophospholipidsformingtheexteriorofthebilayer,andlipoproteinsandphospholipidsformingtheinterior.[32]Theoutermembranetypicallyhasaporousqualityduetoitspresenceofmembraneproteins,suchasgram-negativeporins,whicharepore-formingproteins.Theinner,plasmamembraneisalsogenerallysymmetricwhereastheoutermembraneisasymmetricbecauseofproteinssuchastheaforementioned.Also,fortheprokaryoticmembranes,therearemultiplethingsthatcanaffectthefluidity.Oneofthemajorfactorsthatcanaffectthefluidityisfattyacidcomposition.Forexample,whenthebacteriaStaphylococcusaureuswasgrownin37◦Cfor24h,themembraneexhibitedamorefluidstateinsteadofagel-likestate.Thissupportstheconceptthatinhighertemperatures,themembraneismorefluidthanincoldertemperatures.Whenthemembraneisbecomingmorefluidandneedstobecomemorestabilized,itwillmakelongerfattyacidchainsorsaturatedfattyacidchainsinordertohelpstabilizethemembrane.[33]Bacteriaarealsosurroundedbyacellwallcomposedofpeptidoglycan(aminoacidsandsugars).Someeukaryoticcellsalsohavecellwalls,butnonethataremadeofpeptidoglycan.Theoutermembraneofgramnegativebacteriaisrichinlipopolysaccharides,whicharecombinedpoly-oroligosaccharideandcarbohydratelipidregionsthatstimulatethecell'snaturalimmunity.[34]Theoutermembranecanbleboutintoperiplasmicprotrusionsunderstressconditionsoruponvirulencerequirementswhileencounteringahosttargetcell,andthussuchblebsmayworkasvirulenceorganelles.[35]Bacterialcellsprovidenumerousexamplesofthediversewaysinwhichprokaryoticcellmembranesareadaptedwithstructuresthatsuittheorganism'sniche.Forexample,proteinsonthesurfaceofcertainbacterialcellsaidintheirglidingmotion.[36]Manygram-negativebacteriahavecellmembraneswhichcontainATP-drivenproteinexportingsystems.[36] Structures Fluidmosaicmodel AccordingtothefluidmosaicmodelofS.J.SingerandG.L.Nicolson(1972),whichreplacedtheearliermodelofDavsonandDanielli,biologicalmembranescanbeconsideredasatwo-dimensionalliquidinwhichlipidandproteinmoleculesdiffusemoreorlesseasily.[37]Althoughthelipidbilayersthatformthebasisofthemembranesdoindeedformtwo-dimensionalliquidsbythemselves,theplasmamembranealsocontainsalargequantityofproteins,whichprovidemorestructure.Examplesofsuchstructuresareprotein-proteincomplexes,picketsandfencesformedbytheactin-basedcytoskeleton,andpotentiallylipidrafts. Lipidbilayer Diagramofthearrangementofamphipathiclipidmoleculestoformalipidbilayer.Theyellowpolarheadgroupsseparatethegreyhydrophobictailsfromtheaqueouscytosolicandextracellularenvironments. Lipidbilayersformthroughtheprocessofself-assembly.Thecellmembraneconsistsprimarilyofathinlayerofamphipathicphospholipidsthatspontaneouslyarrangesothatthehydrophobic"tail"regionsareisolatedfromthesurroundingwaterwhilethehydrophilic"head"regionsinteractwiththeintracellular(cytosolic)andextracellularfacesoftheresultingbilayer.Thisformsacontinuous,sphericallipidbilayer.Hydrophobicinteractions(alsoknownasthehydrophobiceffect)arethemajordrivingforcesintheformationoflipidbilayers.Anincreaseininteractionsbetweenhydrophobicmolecules(causingclusteringofhydrophobicregions)allowswatermoleculestobondmorefreelywitheachother,increasingtheentropyofthesystem.ThiscomplexinteractioncanincludenoncovalentinteractionssuchasvanderWaals,electrostaticandhydrogenbonds. Lipidbilayersaregenerallyimpermeabletoionsandpolarmolecules.Thearrangementofhydrophilicheadsandhydrophobictailsofthelipidbilayerpreventpolarsolutes(ex.aminoacids,nucleicacids,carbohydrates,proteins,andions)fromdiffusingacrossthemembrane,butgenerallyallowsforthepassivediffusionofhydrophobicmolecules.Thisaffordsthecelltheabilitytocontrolthemovementofthesesubstancesviatransmembraneproteincomplexessuchaspores,channelsandgates. Flippasesandscramblasesconcentratephosphatidylserine,whichcarriesanegativecharge,ontheinnermembrane.AlongwithNANA,thiscreatesanextrabarriertochargedmoietiesmovingthroughthemembrane. Membranesservediversefunctionsineukaryoticandprokaryoticcells.Oneimportantroleistoregulatethemovementofmaterialsintoandoutofcells.Thephospholipidbilayerstructure(fluidmosaicmodel)withspecificmembraneproteinsaccountsfortheselectivepermeabilityofthemembraneandpassiveandactivetransportmechanisms.Inaddition,membranesinprokaryotesandinthemitochondriaandchloroplastsofeukaryotesfacilitatethesynthesisofATPthroughchemiosmosis.[38] Membranepolarity Seealso:Epithelialpolarity Alphaintercalatedcell Theapicalmembraneofapolarizedcellisthesurfaceoftheplasmamembranethatfacesinwardtothelumen.Thisisparticularlyevidentinepithelialandendothelialcells,butalsodescribesotherpolarizedcells,suchasneurons.Thebasolateralmembraneofapolarizedcellisthesurfaceoftheplasmamembranethatformsitsbasalandlateralsurfaces.Itfacesoutwards,towardstheinterstitium,andawayfromthelumen.Basolateralmembraneisacompoundphrasereferringtotheterms"basal(base)membrane"and"lateral(side)membrane",which,especiallyinepithelialcells,areidenticalincompositionandactivity.Proteins(suchasionchannelsandpumps)arefreetomovefromthebasaltothelateralsurfaceofthecellorviceversainaccordancewiththefluidmosaicmodel.Tightjunctionsjoinepithelialcellsneartheirapicalsurfacetopreventthemigrationofproteinsfromthebasolateralmembranetotheapicalmembrane.Thebasalandlateralsurfacesthusremainroughlyequivalent[clarificationneeded]tooneanother,yetdistinctfromtheapicalsurface. Membranestructures DiagramoftheCellMembrane'sstructures. Cellmembranecanformdifferenttypesof"supramembrane"structuressuchascaveola,postsynapticdensity,podosome,invadopodium,focaladhesion,anddifferenttypesofcelljunctions.Thesestructuresareusuallyresponsibleforcelladhesion,communication,endocytosisandexocytosis.Theycanbevisualizedbyelectronmicroscopyorfluorescencemicroscopy.Theyarecomposedofspecificproteins,suchasintegrinsandcadherins. Cytoskeleton Thecytoskeletonisfoundunderlyingthecellmembraneinthecytoplasmandprovidesascaffoldingformembraneproteinstoanchorto,aswellasformingorganellesthatextendfromthecell.Indeed,cytoskeletalelementsinteractextensivelyandintimatelywiththecellmembrane.[39]Anchoringproteinsrestrictsthemtoaparticularcellsurface—forexample,theapicalsurfaceofepithelialcellsthatlinethevertebrategut—andlimitshowfartheymaydiffusewithinthebilayer.Thecytoskeletonisabletoformappendage-likeorganelles,suchascilia,whicharemicrotubule-basedextensionscoveredbythecellmembrane,andfilopodia,whichareactin-basedextensions.Theseextensionsareensheathedinmembraneandprojectfromthesurfaceofthecellinordertosensetheexternalenvironmentand/ormakecontactwiththesubstrateorothercells.Theapicalsurfacesofepithelialcellsaredensewithactin-basedfinger-likeprojectionsknownasmicrovilli,whichincreasecellsurfaceareaandtherebyincreasetheabsorptionrateofnutrients.Localizeddecouplingofthecytoskeletonandcellmembraneresultsinformationofableb. Intracellularmembranes Thecontentofthecell,insidethecellmembrane,iscomposedofnumerousmembrane-boundorganelles,whichcontributetotheoverallfunctionofthecell.Theorigin,structure,andfunctionofeachorganelleleadstoalargevariationinthecellcompositionduetotheindividualuniquenessassociatedwitheachorganelle. Mitochondriaandchloroplastsareconsideredtohaveevolvedfrombacteria,knownastheendosymbiotictheory.ThistheoryarosefromtheideathatParacoccusandRhodopseudomonas,typesofbacteria,sharesimilarfunctionstomitochondriaandblue-greenalgae,orcyanobacteria,sharesimilarfunctionstochloroplasts.Theendosymbiotictheoryproposesthatthroughthecourseofevolution,aeukaryoticcellengulfedthese2typesofbacteria,leadingtotheformationofmitochondriaandchloroplastsinsideeukaryoticcells.Thisengulfmentleadtothe2membranessystemsoftheseorganellesinwhichtheoutermembraneoriginatedfromthehost'splasmamembraneandtheinnermembranewastheendosymbiont'splasmamembrane.ConsideringthatmitochondriaandchloroplastsbothcontaintheirownDNAisfurthersupportthatbothoftheseorganellesevolvedfromengulfedbacteriathatthrivedinsideaeukaryoticcell.[40] Ineukaryoticcells,thenuclearmembraneseparatesthecontentsofthenucleusfromthecytoplasmofthecell.[41]Thenuclearmembraneisformedbyaninnerandoutermembrane,providingthestrictregulationofmaterialsintoandoutofthenucleus.Materialsmovebetweenthecytosolandthenucleusthroughnuclearporesinthenuclearmembrane.Ifacell'snucleusismoreactiveintranscription,itsmembranewillhavemorepores.Theproteincompositionofthenucleuscanvarygreatlyfromthecytosolasmanyproteinsareunabletocrossthroughporesviadiffusion.Withinthenuclearmembrane,theinnerandoutermembranesvaryinproteincomposition,andonlytheoutermembraneiscontinuouswiththeendoplasmicreticulum(ER)membrane.LiketheER,theoutermembranealsopossessesribosomesresponsibleforproducingandtransportingproteinsintothespacebetweenthetwomembranes.Thenuclearmembranedisassemblesduringtheearlystagesofmitosisandreassemblesinlaterstagesofmitosis.[42] TheER,whichispartoftheendomembranesystem,whichmakesupaverylargeportionofthecell'stotalmembranecontent.TheERisanenclosednetworkoftubulesandsacs,anditsmainfunctionsincludeproteinsynthesis,andlipidmetabolism.Thereare2typesofER,smoothandrough.TheroughERhasribosomesattachedtoitusedforproteinsynthesis,whilethesmoothERisusedmorefortheprocessingoftoxinsandcalciumregulationinthecell.[43] TheGolgiapparatushastwointerconnectedroundGolgicisternae.Compartmentsoftheapparatusformsmultipletubular-reticularnetworksresponsiblefororganization,stackconnectionandcargotransportthatdisplayacontinuousgrape-likestringedvesiclesrangingfrom50-60 nm.Theapparatusconsistsofthreemaincompartments,aflatdisc-shapedcisternawithtubular-reticularnetworksandvesicles.[44] Variations Thecellmembranehasdifferentlipidandproteincompositionsindistincttypesofcellsandmayhavethereforespecificnamesforcertaincelltypes. Sarcolemmainmusclecells:Sarcolemmaisthenamegiventothecellmembraneofmusclecells.[45]Althoughthesarcolemmaissimilartoothercellmembranes,ithasotherfunctionsthatsetitapart.Forinstance,thesarcolemmatransmitssynapticsignals,helpsgenerateactionpotentials,andisveryinvolvedinmusclecontraction.[46]Unlikeothercellmembranes,thesarcolemmamakesupsmallchannelscalledT-tubulesthatpassthroughtheentiretyofmusclecells.Ithasalsobeenfoundthattheaveragesarcolemmais10 nmthickasopposedtothe4 nmthicknessofageneralcellmembrane.[47][45] Oolemmaisthecellmembraneinoocytes:Theoolemmaofoocytes,(immatureeggcells)arenotconsistentwithalipidbilayerastheylackabilayeranddonotconsistoflipids.[48]Rather,thestructurehasaninnerlayer,thefertilizationenvelope,andtheexteriorismadeupofthevitellinelayer,whichismadeupofglycoproteins;however,channelsandproteinsarestillpresentfortheirfunctionsinthemembrane. Axolemma:Thespecializedplasmamembraneontheaxonsofnervecellsthatisresponsibleforthegenerationoftheactionpotential.Itconsistsofagranular,denselypackedlipidbilayerthatworkscloselywiththecytoskeletoncomponentsspectrinandactin.Thesecytoskeletoncomponentsareabletobindtoandinteractwithtransmembraneproteinsintheaxolemma.[49][50] Permeability Seealso:Intestinalpermeability Thepermeabilityofamembraneistherateofpassivediffusionofmoleculesthroughthemembrane.Thesemoleculesareknownaspermeantmolecules.Permeabilitydependsmainlyontheelectricchargeandpolarityofthemoleculeandtoalesserextentthemolarmassofthemolecule.Duetothecellmembrane'shydrophobicnature,smallelectricallyneutralmoleculespassthroughthemembranemoreeasilythancharged,largeones.TheinabilityofchargedmoleculestopassthroughthecellmembraneresultsinpHpartitionofsubstancesthroughoutthefluidcompartmentsofthebody. Seealso Annularlipidshell Artificialcell Bacterialcellstructure Bangstadsyndrome Cellcortex Celldamage,includingdamagetocellmembrane Celltheory Cytoneme Elasticityofcellmembranes Gram-positivebacteria Membranemodels Membranenanotubule Historyofcellmembranetheory Lipidraft Trogocytosis Notesandreferences ^Kimball'sBiologypagesArchived2009-01-25attheWaybackMachine,CellMembranes ^SingletonP(1999).BacteriainBiology,BiotechnologyandMedicine(5th ed.).NewYork:Wiley.ISBN 978-0-471-98880-9. ^TomHerrmann1;SandeepSharma2.(March2,2019)."Physiology,Membrane".StatPearls.1SIUSchoolofMedicine2BaptistRegionalMedicalCenter.PMID 30855799.CS1maint:usesauthorsparameter(link)CS1maint:location(link) ^abcdefghAlbertsB,JohnsonA,LewisJ,et al.(2002).MolecularBiologyoftheCell(4th ed.).NewYork:GarlandScience.ISBN 978-0-8153-3218-3.Archivedfromtheoriginalon2017-12-20. ^BudinI,DevarajNK(January2012)."Membraneassemblydrivenbyabiomimeticcouplingreaction".JournaloftheAmericanChemicalSociety.134(2):751–3.doi:10.1021/ja2076873.PMC 3262119.PMID 22239722. ^Staff(January25,2012)."ChemistsSynthesizeArtificialCellMembrane".ScienceDaily.ArchivedfromtheoriginalonJanuary29,2012.RetrievedFebruary18,2012. ^Staff(January26,2012)."Chemistscreateartificialcellmembrane".kurzweilai.net.ArchivedfromtheoriginalonFebruary26,2012.RetrievedFebruary18,2012. ^Zeidi,Mahdi;Kim,ChunIL(2018)."Theeffectsofintra-membraneviscosityonlipidmembranemorphology:completeanalyticalsolution".ScientificReports.8(1):12845.Bibcode:2018NatSR...812845Z.doi:10.1038/s41598-018-31251-6.ISSN 2045-2322.PMC 6110749.PMID 30150612. ^abcdefgLombardJ(December2014)."Onceuponatimethecellmembranes:175yearsofcellboundaryresearch".BiologyDirect.9:32.doi:10.1186/s13062-014-0032-7.PMC 4304622.PMID 25522740. ^Leray,C.Chronologicalhistoryoflipidcenter.CyberlipidCenter.Lastupdatedon11November2017.linkArchived2017-10-13attheWaybackMachine. ^GorterE,GrendelF(March1925)."OnBimolecularLayersofLipoidsontheChromocytesoftheBlood".TheJournalofExperimentalMedicine.41(4):439–43.doi:10.1084/jem.41.4.439.PMC 2130960.PMID 19868999. ^SJSingerandGLNicolson."Thefluidmosaicmodelofthestructureofcellmembranes."Science.(1972)175.720-731. ^deVriesH(1885)."PlasmolytischeStudienüberdieWandderVakuolen".Jahrb.Wiss.Bot.16:465–598. ^Pfeffer,W.1877.OsmotischeUntersuchungen:StudienzurZellMechanik.Engelmann,Leipzig. ^Pfeffer,W.,1900–1906.ThePhysiologyofPlants,[1]Archived2018-06-02attheWaybackMachine.TranslatedbyA.J.Ewartfromthe2ndGermaned.ofPflanzenphysiologie,1897-1904,[2]Archived2018-06-01attheWaybackMachine.ClarendonPress,Oxford. ^Sharp,L.W.(1921).IntroductionToCytology.NewYork:McGrawHill,p.42. ^Kleinzeller,A.1999.CharlesErnestOverton’sconceptofacellmembrane.In:Membranepermeability:100yearssinceErnestOverton(ed.DeamerD.W.,KleinzellerA.,FambroughD.M.),pp.1–18,AcademicPress,SanDiego,[3]. ^MastSO(1924)."StructureandlocomotioninAmoebaproteus".Anat.Rec.29(2):88.doi:10.1002/ar.1090290205. ^PloweJQ(1931)."Membranesintheplantcell.I.Morphologicalmembranesatprotoplasmicsurfaces".Protoplasma.12:196–220.doi:10.1007/BF01618716.S2CID 32248784. ^WayneR(2009).PlantCellBiology:FromAstronomytoZoology.Amsterdam:Elsevier/AcademicPress.p. 17.ISBN 9780080921273. ^NoutsiP,GrattonE,ChaiebS(2016-06-30)."AssessmentofMembraneFluidityFluctuationsduringCellularDevelopmentRevealsTimeandCellTypeSpecificity".PLOSONE.11(6):e0158313.Bibcode:2016PLoSO..1158313N.doi:10.1371/journal.pone.0158313.PMC 4928918.PMID 27362860. ^abcLodishH,BerkA,ZipurskyLS,et al.(2000)."Biomembranes:StructuralOrganizationandBasicFunctions".MolecularCellBiology(4th ed.).NewYork:ScientificAmericanBooks.ISBN 978-0-7167-3136-8. ^abcCooperGM(2000)."StructureofthePlasmaMembrane".TheCell:AMolecularApproach(2nd ed.).Archivedfromtheoriginalon2017-09-19. ^abLodishH,BerkA,ZipurskySL,MatsudairaP,BaltimoreD,DarnellJ(2000)."Biomembranes:StructuralOrganizationandBasicFunctions".MolecularCellBiology(4th ed.).Archivedfromtheoriginalon2018-06-05. ^abBrandleyBK,SchnaarRL(July1986)."Cell-surfacecarbohydratesincellrecognitionandresponse".JournalofLeukocyteBiology.40(1):97–111.doi:10.1002/jlb.40.1.97.PMID 3011937.S2CID 45528175. ^JesseGray;ShanaGroeschler;TonyLe;ZaraGonzalez(2002)."MembraneStructure"(SWF).DavidsonCollege.Archivedfromtheoriginalon2007-01-08.Retrieved2007-01-11. ^LodishH,BerkA,ZipurskySL,MatsudairaP,BaltimoreD,DarnellJ(2000)."Post-TranslationalModificationsandQualityControlintheRoughER".MolecularCellBiology(4th ed.). ^Cooper,GeoffreyM.(2000)."TransportofSmallMolecules".TheCell:AMolecularApproach(2nd ed.).Archivedfromtheoriginalon2018-06-05. ^KramerEM,MyersDR(April2013)."Osmosisisnotdrivenbywaterdilution".TrendsinPlantScience.18(4):195–7.doi:10.1016/j.tplants.2012.12.001.PMID 23298880. ^abAlbertsB,JohnsonA,LewisJ,RaffM,RobertsK,WalterP(2002)."MembraneProteins".MolecularBiologyoftheCell(4th ed.).Archivedfromtheoriginalon2018-06-05. ^AlbertsB,JohnsonA,LewisJ,RaffM,RobertsK,WalterP(2002)."TransportintotheCellfromthePlasmaMembrane:Endocytosis".MolecularBiologyoftheCell(4th ed.).GarlandScience.Archivedfromtheoriginalon2018-06-05. ^SaltonMR,KimK(1996).BaronS(ed.).MedicalMicrobiology(4th ed.).Galveston(TX):UniversityofTexasMedicalBranchatGalveston.ISBN 978-0963117212.PMID 21413343. ^MishraNN,LiuGY,YeamanMR,NastCC,ProctorRA,McKinnellJ,BayerAS(February2011)."Carotenoid-relatedalterationofcellmembranefluidityimpactsStaphylococcusaureussusceptibilitytohostdefensepeptides".AntimicrobialAgentsandChemotherapy.55(2):526–31.doi:10.1128/AAC.00680-10.PMC 3028772.PMID 21115796. ^AlexanderC,RietschelET(2001)."Bacteriallipopolysaccharidesandinnateimmunity".JournalofEndotoxinResearch.7(3):167–202.doi:10.1177/09680519010070030101.PMID 11581570.S2CID 86224757. ^YashRoyRC(1999)."AstructuralmodelforvirulenceorganellaeofgramnegativeorganismswithreferencetoSalmonellapathogenicityinchickenileum".IndianJournalofPoultryScience.34(2):213–219.Archivedfromtheoriginalon2014-11-07. ^abSaierMH(2013)."Microcompartmentsandproteinmachinesinprokaryotes".JournalofMolecularMicrobiologyandBiotechnology.23(4–5):243–69.doi:10.1159/000351625.PMC 3832201.PMID 23920489. ^SingerSJ,NicolsonGL(February1972)."Thefluidmosaicmodelofthestructureofcellmembranes".Science.175(4023):720–31.Bibcode:1972Sci...175..720S.doi:10.1126/science.175.4023.720.PMID 4333397.S2CID 83851531. ^Zeidi,Mahdi;Kim,ChunIL(2018)."Theeffectsofintra-membraneviscosityonlipidmembranemorphology:completeanalyticalsolution".ScientificReports.8(1):12845.Bibcode:2018NatSR...812845Z.doi:10.1038/s41598-018-31251-6.ISSN 2045-2322.PMC 6110749.PMID 30150612. ^DohertyGJ,McMahonHT(2008)."Mediation,modulation,andconsequencesofmembrane-cytoskeletoninteractions".AnnualReviewofBiophysics.37:65–95.doi:10.1146/annurev.biophys.37.032807.125912.PMID 18573073.S2CID 17352662. ^WhatleyJM,JohnP,WhatleyFR(April1979)."Fromextracellulartointracellular:theestablishmentofmitochondriaandchloroplasts".ProceedingsoftheRoyalSocietyofLondon.SeriesB,BiologicalSciences.204(1155):165–87.Bibcode:1979RSPSB.204..165W.doi:10.1098/rspb.1979.0020.PMID 36620.S2CID 42398067. ^AlbertsB,JohnsonA,LewisJ,RaffM,RobertsK,WalterP(2002)."TheStructureandFunctionofDNA".MolecularBiologyoftheCell(4th ed.).GarlandScience. ^AlbertsB,JohnsonA,LewisJ,RaffM,RobertsK,WalterP(2002)."TheTransportofMoleculesbetweentheNucleusandtheCytosol".MolecularBiologyoftheCell(4th ed.).GarlandScience. ^CooperGM(2000)."TheEndoplasmicReticulum".TheCell:AMolecularApproach(2nd ed.).Archivedfromtheoriginalon2017-10-03. ^XuH,SuW,CaiM,JiangJ,ZengX,WangH(2013-04-16)."TheasymmetricalstructureofGolgiapparatusmembranesrevealedbyinsituatomicforcemicroscope".PLOSONE.8(4):e61596.Bibcode:2013PLoSO...861596X.doi:10.1371/journal.pone.0061596.PMC 3628984.PMID 23613878. ^abReedR,WoustonTW,ToddPM(July1966)."Structureandfunctionofthesarcolemmaofskeletalmuscle".Nature.211(5048):534–6.Bibcode:1966Natur.211..534R.doi:10.1038/211534b0.PMID 5967498.S2CID 4183025. ^CampbellKP,StullJT(April2003)."Skeletalmusclebasementmembrane-sarcolemma-cytoskeletoninteractionminireviewseries".TheJournalofBiologicalChemistry.278(15):12599–600.doi:10.1074/jbc.r300005200.PMID 12556456. ^MitraK,Ubarretxena-BelandiaI,TaguchiT,WarrenG,EngelmanDM(March2004)."Modulationofthebilayerthicknessofexocyticpathwaymembranesbymembraneproteinsratherthancholesterol".ProceedingsoftheNationalAcademyofSciencesoftheUnitedStatesofAmerica.101(12):4083–8.Bibcode:2004PNAS..101.4083M.doi:10.1073/pnas.0307332101.PMC 384699.PMID 15016920. ^WesselGM,WongJL(October2009)."Cellsurfacechangesintheeggatfertilization".MolecularReproductionandDevelopment.76(10):942–53.doi:10.1002/mrd.21090.PMC 2842880.PMID 19658159. ^RaineCS(1999)."CharacteristicsoftheNeuron".BasicNeurochemistry:Molecular,CellularandMedicalAspects(6th ed.). ^FitzpatrickMO,MaxwellWL,GrahamDI(March1998)."Theroleoftheaxolemmaintheinitiationoftraumaticallyinducedaxonalinjury".JournalofNeurology,Neurosurgery,andPsychiatry.64(3):285–7.doi:10.1136/jnnp.64.3.285.PMC 2169978.PMID 9527135. Externallinks WikimediaCommonshasmediarelatedtoCellmembrane. WikiversityhaslearningresourcesaboutTheCellMembrane Lipids,MembranesandVesicleTrafficking-TheVirtualLibraryofBiochemistryandCellBiology Cellmembraneproteinextractionprotocol Membranehomeostasis,tensionregulation,mechanosensitivemembraneexchangeandmembranetraffic 3Dstructuresofproteinsassociatedwithplasmamembraneofeukaryoticcells Lipidcompositionandproteinsofsomeeukarioticmembranes [4] vteStructuresofthecell/organellesEndomembranesystem Cellmembrane Nucleus Endoplasmicreticulum Golgiapparatus Parenthesome Autophagosome Vesicle Exosome Lysosome Endosome Phagosome Vacuole Acrosome Cytoplasmicgranule Melanosome Microbody Glyoxysome Peroxisome Weibel–Paladebody Cytoskeleton Microfilament Intermediatefilament Microtubule Prokaryoticcytoskeleton Microtubuleorganizingcenter Centrosome Centriole Basalbody Spindlepolebody Myofibril Undulipodium Cilium Flagellum Axoneme Radialspoke Pseudopodium Lamellipodium Filopodium Endosymbionts Mitochondrion Plastid Chloroplast Chromoplast Gerontoplast Leucoplast Amyloplast Elaioplast Proteinoplast Tannosome Otherinternal Nucleolus RNA Ribosome Spliceosome Vault Cytoplasm Cytosol Inclusions Proteasome Magnetosome External Cellwall Extracellularmatrix vteStructuresofthecellmembraneMembranelipids Lipidbilayer Phospholipids Lipoproteins Sphingolipids Sterols Membraneproteins Membraneglycoproteins Integralmembraneproteins/transmembraneprotein Peripheralmembraneprotein/Lipid-anchoredprotein Other Caveolae/Coatedpits Celljunctions Glycocalyx Lipidraft/microdomains Membranecontactsites Membranenanotubes Myelinsheath NodesofRanvier Nuclearenvelope Phycobilisomes Porosomes vteMembranetransportMechanismsforchemicaltransportthroughbiologicalmembranesPassivetransport Simplediffusion(ornon-mediatedtransport) Facilitateddiffusion Osmosis Channels Carriers Activetransport Uniporter Symporter Antiporter Primaryactivetransport Secondaryactivetransport CytosisEndocytosis Efferocytosis Non-specific,adsorptivepinocytosis Phagocytosis Pinocytosis Potocytosis Receptor-mediatedendocytosis Transcytosis ExocytosisDegranulation AuthoritycontrolGeneral IntegratedAuthorityFile(Germany) Nationallibraries France(data) Ukraine UnitedStates Japan Other MicrosoftAcademic 2 Retrievedfrom"https://en.wikipedia.org/w/index.php?title=Cell_membrane&oldid=1054976227" Categories:MembranebiologyOrganellesCellanatomyHiddencategories:WebarchivetemplatewaybacklinksCS1maint:usesauthorsparameterCS1maint:locationWikipediapagessemi-protectedagainstvandalismArticleswithshortdescriptionShortdescriptionisdifferentfromWikidataWikipediaarticlesneedingclarificationfromOctober2012CommonscategorylinkisonWikidataArticleswithGNDidentifiersArticleswithBNFidentifiersArticleswithEMUidentifiersArticleswithLCCNidentifiersArticleswithNDLidentifiersArticleswithMAidentifiersArticleswithmultipleidentifiers Navigationmenu Personaltools NotloggedinTalkContributionsCreateaccountLogin Namespaces ArticleTalk Variants expanded collapsed Views ReadViewsourceViewhistory More expanded collapsed Search Navigation MainpageContentsCurrenteventsRandomarticleAboutWikipediaContactusDonate Contribute HelpLearntoeditCommunityportalRecentchangesUploadfile Tools WhatlinkshereRelatedchangesUploadfileSpecialpagesPermanentlinkPageinformationCitethispageWikidataitem Print/export DownloadasPDFPrintableversion Inotherprojects WikimediaCommons Languages العربيةAzərbaycancaবাংলাБеларускаяБългарскиBosanskiCatalàČeštinaCymraegDanskالدارجةDeutschEestiΕλληνικάEspañolEsperantoEuskaraفارسیFrançaisGaeilgeGaelgGalego한국어Հայերենहिन्दीHrvatskiBahasaIndonesiaÍslenskaItalianoעבריתJawaქართულიҚазақшаKiswahiliKreyòlayisyenKurdîКыргызчаLatinaLatviešuLëtzebuergeschLietuviųLombardMagyarМакедонскиമലയാളംBahasaMelayuNederlands日本語NorskbokmålNorsknynorskOccitanOʻzbekcha/ўзбекчаپښتوPolskiPortuguêsRomânăРусскийSimpleEnglishSlovenčinaSlovenščinaСрпски/srpskiSrpskohrvatski/српскохрватскиSundaSuomiSvenskaTagalogதமிழ்ไทยTürkçeУкраїнськаاردوئۇيغۇرچە/UyghurcheTiếngViệt吴语粵語中文 Editlinks



請為這篇文章評分?