cell membrane | Definition, Function, & Structure | Britannica

Cell membrane, thin membrane that surrounds every living cell. The cell membrane functions as a barrier, keeping cell constituents in and unwanted ... cellmembrane Sections&Media Article Introduction&QuickFacts FastFacts Facts&RelatedContent Media Videos Images AdditionalInfo MoreArticlesOnThisTopic Contributors ArticleHistory Home Health&Medicine Anatomy&Physiology cellmembrane biology Alternatetitles:plasmamembrane Print Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/science/cell-membrane More GiveFeedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). 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ExternalWebsites HyperPhysics-TheCellMembrane Rader'sBiology4Kids-CellMembranes By TheEditorsofEncyclopaediaBritannica | ViewEditHistory FastFacts Facts&RelatedContent molecularviewofthecellmembrane Seeallmedia KeyPeople: PeterAgre RoderickMacKinnon ...(Showmore) RelatedTopics: ionchannel secondmessenger transientreceptorpotentialchannel extrinsicprotein axonhillock ...(Showmore) Seeallfactsanddata→ cellmembrane,alsocalledplasmamembrane,thinmembranethatsurroundseverylivingcell,delimitingthecellfromtheenvironmentaroundit.Enclosedbythiscellmembrane(alsoknownastheplasmamembrane)arethecell’sconstituents,oftenlarge,water-soluble,highlychargedmoleculessuchasproteins,nucleicacids,carbohydrates,andsubstancesinvolvedincellularmetabolism.Outsidethecell,inthesurroundingwater-basedenvironment,areions,acids,andalkalisthataretoxictothecell,aswellasnutrientsthatthecellmustabsorbinordertoliveandgrow.Thecellmembrane,therefore,hastwofunctions:first,tobeabarrierkeepingtheconstituentsofthecellinandunwantedsubstancesoutand,second,tobeagateallowingtransportintothecellofessentialnutrientsandmovementfromthecellofwasteproducts.Cellmembranesarecomposedprimarilyoffatty-acid-basedlipidsandproteins.Membranelipidsareprincipallyoftwotypes,phospholipidsandsterols(generallycholesterol).Bothtypessharethedefiningcharacteristicoflipids—theydissolvereadilyinorganicsolvents—butinadditiontheybothhavearegionthatisattractedtoandsolubleinwater.This“amphiphilic”property(havingadualattraction;i.e.,containingbothalipid-solubleandawater-solubleregion)isbasictotheroleoflipidsasbuildingblocksofcellularmembranes.Membraneproteinsarealsooftwogeneraltypes.Onetype,calledtheextrinsicproteins,islooselyattachedbyionicbondsorcalciumbridgestotheelectricallychargedphosphorylsurfaceofthebilayer.Theycanalsoattachtothesecondtypeofprotein,calledtheintrinsicproteins.Theintrinsicproteins,astheirnameimplies,arefirmlyembeddedwithinthephospholipidbilayer.Ingeneral,membranesactivelyinvolvedinmetabolismcontainahigherproportionofprotein. ReadMoreonThisTopic cell:Thecellmembrane Athinmembrane,typicallybetween4and10nanometers(nm;1nm=10−9metre)inthickness,surroundseverylivingcell,delimiting... Thechemicalstructureofthecellmembranemakesitremarkablyflexible,theidealboundaryforrapidlygrowinganddividingcells.Yetthemembraneisalsoaformidablebarrier,allowingsomedissolvedsubstances,orsolutes,topasswhileblockingothers.Lipid-solublemoleculesandsomesmallmoleculescanpermeatethemembrane,butthelipidbilayereffectivelyrepelsthemanylarge,water-solublemoleculesandelectricallychargedionsthatthecellmustimportorexportinordertolive.Transportofthesevitalsubstancesiscarriedoutbycertainclassesofintrinsicproteinsthatformavarietyoftransportsystems:someareopenchannels,whichallowionstodiffusedirectlyintothecell;othersare“facilitators,”whichhelpsolutesdiffusepastthelipidscreen;yetothersare“pumps,”whichforcesolutesthroughthemembranewhentheyarenotconcentratedenoughtodiffusespontaneously.Particlestoolargetobediffusedorpumpedareoftenswallowedordisgorgedwholebyanopeningandclosingofthemembrane.Inbringingabouttransmembranemovementsoflargemolecules,thecellmembraneitselfundergoesconcertedmovementsduringwhichpartofthefluidmediumoutsideofthecellisinternalized(endocytosis)orpartofthecell’sinternalmediumisexternalized(exocytosis).Thesemovementsinvolveafusionbetweenmembranesurfaces,followedbythere-formationofintactmembranes.receptor-mediatedendocytosisReceptorsplaykeyrolesinmanycellularprocesses.Forexample,receptor-mediatedendocytosisenablescellstoingestmoleculessuchasproteinsthatarenecessaryfornormalcellfunctioning.EncyclopædiaBritannica,Inc. GetaBritannicaPremiumsubscriptionandgainaccesstoexclusivecontent. SubscribeNow TheEditorsofEncyclopaediaBritannica ThisarticlewasmostrecentlyrevisedandupdatedbyKaraRogers. LearnMoreintheserelatedBritannicaarticles: cell:Thecellmembrane Athinmembrane,typicallybetween4and10nanometers(nm;1nm=10−9metre)inthickness,surroundseverylivingcell,delimitingthecellfromtheenvironmentaroundit.Enclosedbythiscellmembrane(alsoknownastheplasmamembrane)arethecell’s… nervoussystem:Plasmamembrane Theneuronisboundbyaplasmamembrane,astructuresothinthatitsfinedetailcanberevealedonlybyhigh-resolutionelectronmicroscopy.Abouthalfofthemembraneisthelipidbilayer,twosheetsofmainlyphospholipidswithaspacebetween.One… muscle:Themusclefibre Theinnermostlayerisaplasmamembranesimilartotheonesthatsurroundmostcells.Theplasmamembraneconsistsofalipidbilayerwithproteinsembeddedinit.Someoftheproteinsareembeddedentirelywithinthelipidlayer,othersextendtooneortheothersurface,andstillothers… Historyatyourfingertips SignupheretoseewhathappenedOnThisDay,everydayinyourinbox! Emailaddress Bysigningup,youagreetoourPrivacyNotice. Thankyouforsubscribing! 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