Membranes

MembranesChapter 05MembranesBiology, 9th ed,Sylvia MaderMembranesSlide #1Chapter 05Chapter 5 OutlineMembrane ModelsFluid-MosaicPlasma Membrane Structure and FunctionPhospholipidsProteinsPlasma Membrane PermeabilityDiffusionOsmosisTransport Via Carrier ProteinsCell Surface Modifications2MembranesStructure and Function:The Phospholipid BilayerThe plasma membrane is common to all cellsSeparates:Internal living cytoplasmic fromExternal environment of cellPhospholipid bilayer:External surface lined with hydrophilic polar headsCytoplasmic surface lined with hydrophilic polar headsNonpolar, hydrophobic, fatty-acid tails sandwiched in between3MembranesUnit Membrane4

MembranesMembrane ModelsFluid-Mosaic ModelThree components:Basic membrane referred to as phospholipid bilayerProtein moleculesFloat around like icebergs on a seaMembrane proteins may be peripheral or integralPeripheral proteins are found on the inner membrane surfaceIntegral proteins are partially or wholly embedded (transmembrane) in the membraneSome have carbohydrate chains attachedCholesterol5MembranesMembrane Models:Unit Membrane vs. Fluid Mosaic Model6

MembranesThe Fluid Mosaic Model7

MembranesPhospholipid & CholesterolMolecules8

MembranesTransmembrane Proteins9

MembranesLateral Migration ofMembrane Proteins10

MembranesFunctions of Membrane ProteinsChannel Proteins:TubularAllow passage of molecules through membraneCarrier Proteins:Combine with substance to be transportedAssist passage of molecules through membraneCell Recognition Proteins:Provides unique chemical ID for cellsHelp body recognize foreign substancesReceptor Proteins:Binds with messenger moleculeCauses cell to respond to messageEnzymatic Proteins:Carry out metabolic reactions directly11MembranesMembrane Protein Diversity12

MembranesTypes of Transport:Active vs. PassivePlasma membrane is differentially (selectively) permeable Allows some material to passInhibits passage of other materialsPassive Transport:No ATP requirementMolecules follow concentration gradientActive TransportRequires carrier proteinRequires energy in form of ATP13MembranesTypes of Membrane Transport:Overview14

MembranesTypes of Transport:DiffusionA solution consists of:A solvent (liquid) , andA solute (dissolved solid)DiffusionNet movement of solute molecules down a concentration gradientMolecules both ways along gradientMore move from high to low concentration than vice versa Equilibrium:When NET change stopsSolute concentration uniform no gradient15MembranesTypes of Membrane Transport:Diffusion16

MembranesTypes of Membrane Transport:Diffusion Across Lung17

MembranesTypes of Transport:OsmosisOsmosis:Special case of diffusionFocuses on solvent (water) movement rather than soluteDiffusion of water across a differentially (selectively) permeable membraneSolute concentration on one side high, but water concentration lowSolute concentration on other side low, but water concentration highWater diffuses both ways across membrane but solute cantNet movement of water is toward low water (high solute) concentrationOsmotic pressure is the pressure that develops due to osmosis18MembranesTypes of Membrane Transport:Osmosis19

MembranesTypes of Transport:OsmosisIsotonic SolutionSolute and water concentrations equal on both sides of membraneHypotonic Solution Concentration of solute lower than on other sideCells placed in a hypotonic solution will swellMay cause cells to break LysisHypertonic SolutionConcentration of solute higher than on other sideCells placed in a hypertonic solution will shrink Plasmolysis20MembranesOsmotic Effects on Cells21

MembranesTypes of Transport:Carrier ProteinsFacilitated TransportSmall moleculesCant get through membrane lipidsCombine with carrier proteinsFollow concentration gradientActive TransportSmall moleculesMove against concentration gradientCombining with carrier proteinsRequires energy22MembranesTypes of Membrane Transport:Facilitated Transport23

MembranesFacilitated Transport:The Sodium-Potassium Pump24

MembranesTypes of Transport:Membrane-Assisted TransportMacromolecules transported into or out of the cell inside vesiclesExocytosis Vesicles fuse with plasma membrane and secrete contentsEndocytosis Cells engulf substances into pouch which becomes a vesiclePhagocytosis Large, solid material into vesiclePinocytosis Liquid or small, solid particles go into vesicleReceptor-Mediated Specific form of pinocytosis using a coated pit25MembranesMembrane-Assisted Transport:Exocytosis26

MembranesMembrane-Assisted Transport:Three Types of Endocytosis27

MembranesCell Surface Modifications:JunctionsCell Surfaces in AnimalsJunctions Between CellsAdhesion Junctions Intercellular filaments between cellsTight JunctionsForm impermeable barriersGap JunctionsPlasma membrane channels are joined (allows communication)28MembranesCell-Surface Modifications:Junctions29

MembranesCell Surface ModificationsExtracellular MatrixExternal meshwork of polysaccharides and proteinsFound in close association with the cell that produced themPlant Cell WallsPlants have freely permeable cell wall, with cellulose as the main componentPlasmodesmata penetrate cell wallEach contains a strand of cytoplasmAllow passage of material between cells30MembranesCell-Surface Modifications:Extracellular Matrix31

MembranesCell-Surface Modifications:Plasmodesmata32

MembranesReviewMembrane ModelsFluid-MosaicPlasma Membrane Structure and FunctionProtein FunctionsPlasma Membrane PermeabilityDiffusionOsmosisTransport Via Carrier ProteinsCell Surface Modifications33MembranesMembranesEnding Slide Chapter 05Biology, 9th ed,Sylvia MaderMembranesSlide #34Chapter 05