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MDC BSC 2010 - Membrane Structure and Function

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Chapter 7Overview: Life at the EdgePLASMA MEMBRANEThe plasma membrane of the cell is selectively permeable Controlling the flow of substances into or out of the cellSlide 5Concept 7.1: Cellular membranes are fluid mosaics of lipids and proteinsMembrane Models: Scientific InquiryLE 7-2Slide 9LE 7-3Slide 11LE 7-4The Fluidity of MembranesLE 7-5aSlide 15LE 7-5bSlide 17LE 7-5cSlide 19LE 7-6Membrane Proteins and Their FunctionsLE 7-7Slide 23LE 7-8Slide 25Proteins found in the plasma membrane:LE 7-9aLE 7-9bTransport ProteinsThe Role of Membrane Carbohydrates in Cell-Cell RecognitionSlide 31Synthesis and Sidedness of MembranesLE 7-10Concept 7.2: Membrane structure results in selective permeabilityThe Permeability of the Lipid BilayerSlide 36Concept 7.3: Passive transport is diffusion of a substance across a membrane with no energy investmentLE 7-11aTransport Across MembranesSlide 40LE 7-11bEffects of Osmosis on Water BalanceLE 7-12Water Balance of Cells Without WallsSlide 45LE 7-14Water Balance of Cells with WallsLE 7-13Facilitated Diffusion: Passive Transport Aided by ProteinsLE 7-15aLE 7-15bConcept 7.4: Active transport uses energy to move solutes against their gradientsThe Need for Energy in Active TransportLE 7-16LE 7-17MembranesMaintenance of Membrane Potential by Ion PumpsSlide 58LE 7-18Cotransport: Coupled Transport by a Membrane ProteinLE 7-19Concept 7.5: Bulk transport across the plasma membrane occurs by exocytosis and endocytosisExocytosisEndocytosisSlide 65LE 7-20cCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsPowerPoint Lectures for Biology, Seventh EditionNeil Campbell and Jane ReeceLectures by Chris RomeroChapter 7Chapter 7Membrane Structure and FunctionCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsOverview: Life at the Edge•The plasma membrane is the boundary that separates the living cell from its nonliving surroundings•The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than othersCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsPLASMA MEMBRANE•Function:The cell’s “gate keeper”. Very important. It controls what goes in and out of a cell. Keeps equilibrium between the inside of cells and the outside and promotes homeostasis. Web site to check:http://www.wisc-online.com/objects/index_tj.asp?objid=AP1101•Function:The cell’s “gate keeper”. Very important. It controls what goes in and out of a cell. Keeps equilibrium between the inside of cells and the outside and promotes homeostasis. Web site to check:http://www.wisc-online.com/objects/index_tj.asp?objid=AP1101Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsThe plasma membrane of the cell is selectively permeableControlling the flow of substances into or out of the cellCytoplasmOutside of cellTEM 200,000 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsConcept 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 © 2005 Pearson Education, Inc. publishing as Benjamin CummingsMembrane Models: Scientific Inquiry•Membranes have been chemically analyzed and found to be made of proteins and lipids•In 1972, Singer and Nicolson proposed that the membrane is a mosaic of proteins dispersed and individually inserted into the phospholipid bilayerLE 7-2LE 7-2HydrophilicheadHydrophobictailWATERWATERCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings•In 1935, H. Davson and J. 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, Singer and Nicolson proposed that the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to waterLE 7-3LE 7-3Hydrophilic regionof proteinHydrophobic region of proteinPhospholipidbilayerCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings•Freeze-fracture studies of the plasma membrane supported the fluid mosaic model •Freeze-facture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayerLE 7-4LE 7-4KnifeCytoplasmic layerExtracellular layerCytoplasmic layerPlasmamembraneExtracellular layerProteinsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin CummingsThe 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 membraneLE 7-5aLE 7-5aLateral movement(~107 times per second)Flip-flop(~ once per month)Movement of phospholipidsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings•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 oilLE 7-5bLE 7-5bViscousFluidUnsaturated hydrocarbontails with kinksMembrane fluiditySaturated hydro-carbon tailsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings•The steroid cholesterol has different effects on membrane fluidity at different temperatures•At warm temperatures (such as body temp, 37°C), cholesterol restrains movement of phospholipids•At cool temperatures, it maintains fluidity by preventing tight packingLE 7-5cLE 7-5cCholesterolCholesterol within the animal cell membraneCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings•Some proteins in the plasma membrane can drift within the bilayer•Proteins are much larger than lipids and move more slowly•To investigate whether membrane proteins move, researchers fused a mouse cell and a human cellLE 7-6LE 7-6Membrane proteinsMixedproteinsafter1 hourHybrid cellHuman cellMouse


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