PowerPoint Presentation5.1 How Is the Structure of a Membrane Related to Its Function?Slide 3The Plasma MembraneSlide 5Author Animation: Plasma Membrane StructureSlide 7Kinks Increase FluiditySlide 9Author Animation: Cell MembranesSlide 11Slide 12Slide 13Receptor Protein ActivationSlide 15Slide 165.2 How Do Substances Move Across Membranes?Slide 18Diffusion of a Dye in WaterSlide 20Slide 21Slide 22Slide 23Slide 24Slide 25The Effect of Solute Concentration on OsmosisSlide 27The Effects of Osmosis on Red Blood CellsSlide 29Turgor Pressure in Plant CellsSlide 31Slide 32Active TransportSlide 34Slide 35Slide 365.3 How Do Specialized Junctions Allow Cells to Connect and Communicate?Cell Attachment StructuresSlide 39Chapter 5Cell Membrane Structure and Function5.1 How Is the Structure of a Membrane Related to Its Function?Functions of the plasma membrane:1. Isolates cell contents from external environment2. Regulates the exchange of essential substances3. Allows communication within and between cells 4. Creates attachments within and between cells5. Regulates biochemical reactionsMembranes are “fluid mosaics” in which proteins move within layers of lipids–The “fluid mosaic” model of a membrane was proposed in 1972 by Singer & Nicolson – “mosaics” or “a patchwork” of different proteins – Selectively permeable– Allows materials to move in/out of cellglycoproteinporeextracellular fluid (outside)cytoplasm (inside)cholesterolphospholipidbilayertransportproteinreceptorproteinphospholipidrecognitionproteinextra-cellularmatrixenzymecytoskeletoncarbohydratebindingsiteproteinattachmentproteinThe Plasma Membrane Fig. 5-1The phospholipid bilayer is the fluid portion of the membrane– Plasma membranes face both exterior & interior watery environments – Polar hydrophilic heads face outside & inside cell – Nonpolar hydrophobic tails face the inside of the membrane Fig. 5-3extracellular fluid(watery environment)cytoplasm(watery environment)Author Animation: Plasma Membrane StructureThe phospholipid bilayer is the fluid portion of the membrane (continued)– The phospholipid bilayer’s flexible, fluid membrane allows for cellular shape changes – Individual phospholipid molecules are NOT bonded to each other – Some phospholipids have UNsaturated fatty acids that cause “kinks” into their “tails”– The “kinks” make the membrane fluidKinks Increase Fluidity Fig. 5-4more fluid less fluidDOUBLE/TRIPLE BONDS MOSTLY SINGLE BONDSThe phospholipid bilayer is the fluid portion of the membrane (continued)O2, CO2, small nonpolar molecules; some water moleculesGlucose, large polar water-soluable molecules; ions, most water moleculesAuthor Animation: Cell MembranesThe phospholipid bilayer is the fluid portion of the membrane (continued)–Membranes become more fluid at high temperatures (more movement) and less fluid at low temperatures (less movement) –Cholesterol stabilizes membranes, affecting fluidity and reducing permeabilityA variety of proteins form a mosaic within the membrane–Proteins are embedded within, or attached to, the phospholipid bilayer1. Receptor proteins2. Recognition proteins3. Enzymatic proteins4. Attachment proteins5. Transport proteinsA variety of proteins form a mosaic within the membrane (continued)1. Receptor proteins trigger cellular responses upon binding of specific molecules (hormones) sent by other cells 2. Recognition proteins are glycoproteins that serve as identification tags on the surface of a cell (i.e. “nametag”)–Most common are the ones involved in blood typingReceptor Protein Activation Fig. 5-5receptorhormone(cytoplasm)(extracellular fluid) A hormone bindsto the receptor Hormone bindingactivates the receptor,changing its shape The activated receptorstimulates a responsein the cell123A variety of proteins form a mosaic within the membrane (continued)3. Enzymatic proteins are proteins that promote chemical reactions that synthesize or break apart biological molecules 4. Attachment proteins anchor the cell membrane to the inner cytoskeleton, to proteins outside the cell, and to other cellsA variety of proteins form a mosaic within the membrane (continued)5. Transport proteins regulate the movement of hydrophilic molecules through the plasma membrane–Channel proteins form channels to allow specific ions or water molecules to pass through the membrane –Carrier proteins have binding sites that can temporarily attach to specific molecules on one side of the membrane and then move them through the membrane to the other side5.2 How Do Substances Move Across Membranes?Molecules in fluids move in response to gradients–A fluid is a substance whose molecules can flow past one another (have no defined shape)–A solute is a substance that can be dissolved (atoms, ions, or molecules) in a solvent –A solvent is a fluid capable of dissolving a solute –The concentration of a substance defines the amount of solute in a given amount of solvent –A gradient is a physical difference in temperature, pressure, charge, or concentration between two adjoining regions of spaceMolecules in fluids move in response to gradients (continued)–Gradients cause molecules to move from one place to another– Molecules and ions in solution are in constant random motion – An increase in temperature increases the rate of this random motion– Results in net movement from regions of high concentration to regions of low concentration by a process called diffusionDiffusion of a Dye in Water Fig. 5-6 A drop of dye isplaced in water Dye moleculesdiffuse into the water;water molecules diffuseinto the dye Both dye moleculesand water molecules areevenly disperseddrop of dyewater molecule213Movement through membranes occurs by:A. Passive transport is movement of substances across cell membranes down concentration gradients, no energy required B. Energy- requiring transport requires the use of cellular ENERGY B. Energy-requiring transport Table 5-1Passive transport includes:1. simple diffusion 2. facilitated diffusion 3. osmosis Fig. 5-7waterglucosecarrierproteinaquaporinchannelproteinphospho-lipidbilayer(cytoplasm)(extracellularfluid)Cl–O2(a) Simple diffusion throughthe phospholipid bilayer(b) Facilitated diffusionthrough channel proteins(c) Osmosis throughaquaporins or thephospholipid bilayer(d) Facilitated diffusion through carrier proteinsSimple diffusion:
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