Chapter 7Overview: Life at the EdgePowerPoint PresentationConcept 7.1: Cellular membranes are fluid mosaics of lipids and proteinsMembrane Models: Scientific InquirySlide 6Slide 7Slide 8Slide 9Slide 10The Fluidity of MembranesSlide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Membrane Proteins and Their FunctionsSlide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26The Role of Membrane Carbohydrates in Cell-Cell RecognitionSynthesis and Sidedness of MembranesSlide 29Concept 7.2: Membrane structure results in selective permeabilityThe Permeability of the Lipid BilayerTransport ProteinsSlide 33Concept 7.3: Passive transport is diffusion of a substance across a membrane with no energy investmentSlide 35Slide 36Slide 37Slide 38Effects of Osmosis on Water BalanceSlide 40Water Balance of Cells Without WallsSlide 42Slide 43Slide 44Water Balance of Cells with WallsSlide 46Facilitated Diffusion: Passive Transport Aided by ProteinsSlide 48Slide 49Slide 50Concept 7.4: Active transport uses energy to move solutes against their gradientsThe Need for Energy in Active TransportSlide 53Slide 54Slide 55Slide 56Slide 57Slide 58Slide 59Slide 60Slide 61How Ion Pumps Maintain Membrane PotentialSlide 63Slide 64Slide 65Cotransport: Coupled Transport by a Membrane ProteinSlide 67Concept 7.5: Bulk transport across the plasma membrane occurs by exocytosis and endocytosisExocytosisEndocytosisSlide 71Slide 72Slide 73Slide 74Slide 75Slide 77Slide 78Slide 79Slide 80Slide 81You should now be able to:Slide 83Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsPowerPoint® Lecture Presentations for Biology Eighth EditionNeil Campbell and Jane ReeceLectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 7Chapter 7Membrane Structure and FunctionOverview: Life at the Edge•The plasma membrane is the boundary that separates the living cell from its surroundings•The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than othersCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsFig. 7-1Concept 7.1: Cellular membranes are fluid mosaics of lipids and proteins•Phospholipids are the most abundant lipid in the plasma membrane•Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions•The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in itCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsMembrane Models: Scientific Inquiry•Membranes have been chemically analyzed and found to be made of proteins and lipids•Scientists studying the plasma membrane reasoned that it must be a phospholipid bilayer Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsFig. 7-2HydrophilicheadWATERHydrophobictailWATER•In 1935, Hugh Davson and James Danielli proposed a sandwich model in which the phospholipid bilayer lies between two layers of globular proteins•Later studies found problems with this model, particularly the placement of membrane proteins, which have hydrophilic and hydrophobic regions•In 1972, J. Singer and G. Nicolson proposed that the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsFig. 7-3PhospholipidbilayerHydrophobic regionsof proteinHydrophilicregions of protein•Freeze-fracture studies of the plasma membrane supported the fluid mosaic model •Freeze-fracture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayerCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsFig. 7-4TECHNIQUEExtracellularlayerKnifeProteinsInside of extracellular layerRESULTSInside of cytoplasmic layerCytoplasmic layerPlasma membraneThe Fluidity of Membranes•Phospholipids in the plasma membrane can move within the bilayer•Most of the lipids, and some proteins, drift laterally•Rarely does a molecule flip-flop transversely across the membraneCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsFig. 7-5Lateral movement(~107 times per second)Flip-flop(~ once per month)(a) Movement of phospholipids(b) Membrane fluidityFluidViscousUnsaturated hydrocarbontails with kinksSaturated hydro-carbon tails(c) Cholesterol within the animal cell membraneCholesterolFig. 7-5a(a) Movement of phospholipidsLateral movement(107 times per second)Flip-flop( once per month)Fig. 7-6RESULTSMembrane proteinsMouse cellHuman cellHybrid cellMixed proteinsafter 1 hour•As temperatures cool, membranes switch from a fluid state to a solid state•The temperature at which a membrane solidifies depends on the types of lipids•Membranes rich in unsaturated fatty acids are more fluid that those rich in saturated fatty acids•Membranes must be fluid to work properly; they are usually about as fluid as salad oilCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsFig. 7-5b(b) Membrane fluidityFluidUnsaturated hydrocarbontails with kinksViscousSaturated hydro-carbon tails•The steroid cholesterol has different effects on membrane fluidity at different temperatures•At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids•At cool temperatures, it maintains fluidity by preventing tight packingCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsFig. 7-5cCholesterol(c) Cholesterol within the animal cell membraneMembrane Proteins and Their Functions•A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer•Proteins determine most of the membrane’s specific functionsCopyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin CummingsFig. 7-7Fibers ofextracellularmatrix (ECM)Glyco-proteinMicrofilamentsof cytoskeletonCholesterolPeripheralproteinsIntegralproteinCYTOPLASMIC SIDEOF MEMBRANEGlycolipidEXTRACELLULARSIDE OFMEMBRANECarbohydrate•Peripheral proteins are bound to the surface of the membrane•Integral proteins penetrate the hydrophobic core •Integral proteins that span the membrane are called transmembrane proteins•The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, often coiled into alpha