Transcript
CellBiology2.4CellMembrane
Essen5alQues5on:Thestructureofbiologicalmembranesmakethemfluidanddynamic
Function of the Cell Membrane • Hold the cell together
• Isolate the cytoplasm and organelles from external environment
• Protect the cell • Regulate the exchange of
substances • Control what goes in and out
• To bind to other cells and molecules
• Cell identification • Allow cell to be recognized and to
recognize (cell signaling, immunity)
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Structure of the Cell Membrane
Phospholipids Primary structural building block of the plasma membrane
Hydrophobic hydrocarbon tails
Water repelled
Hydrophilic phosphate heads
Water attracted
Amphipathic Phospholipids contain both
hydrophilic (water-loving) and lipophilic (fat-loving) regions.
Phospholipids Arrangement in Membranes
• Spontaneouslyarrangesintoabilayer• Bilayerisheldtogetherbyweakhydrophobicinterac5ons
betweenthetails• Amphipathiclayersrestrictthepassageofmanysubstances• Individualphospholipidscanmovewithinthebilayercreate
fluidityandflexibility• Allowsforspontaneousbreakingandreformingofmembrane
Cholesterol(eg.Lipoprotein)Animportantstructuralelementofanimalcellmembranes
• Providesstrengthandstabilitytothemembranestructure• Makesmembranelessfluidbybindingtogetherthelipidinthe
plasmamembrane
Glycolipid• PhospholipidwithaCHOaNached• Provideenergy• Cellularrecogni5onmarkersforspecificelements
Proteins• Servemanyfunc5onsdependingonstructureandloca5on
• Maybeintegral(embedded)orperipheral(ontheinsidesurfaceofmembrane)
-Theseproteinscansitononeofthesurfaces.-Theyslidearoundthemembranequicklyandcollidewithoneanother.-Theycanneverflipfromonesidetotheother.-Involvedinmaintainingcellshape,orcellmo5lity.Mayalsobeenzymes,catalysingreac5onsincytoplasm
Theseproteinscanspanfromonesideofthebilayertotheother.Becausetheyspanthemembrane,theyareoUeninvolvedinthetransportofsubstancesacrossthemembrane.
Glycoprotein• ProteinwithaCHOa1ached• Importantforcell-cellinterac5ons• Importantforwhitebloodcellrecogni5on• Actasreceptorsincellsignaling(suchaswithhormones)
• wasbasicallya"sandwich"oflipids(arrangedinabilayer)coveredonbothsideswithproteins
• thismodelisNOTcorrectbutshowstheprogressionofthecurrentmodel
• oneofthefirstmodelsofmembranetobeacceptedbybiologistsformanyyears.
Davson–DanielliModel(1930’s)
ModelsoftheCellMembrane
CellCytoplasm
ExtracellularEnvironment
• S.J.SingerandNicolson(1966)• Semipermeablemembrane• “fluid”por5onisdoublelayerofphospholipids
(=phospholipidbilayer)• “mosaic”por5onistheproteinsandcarbohydrates
embeddedinthemembrane
FluidMosiacModel
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