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Chapter 7 Outline Membrane Structure and Function Guiding Questions 1. Describe the structure of the cell membrane. 2. By what methods are substances transported across membranes? Fluid Mosaic Model The membrane is a fluid structure with various proteins embedded in or attached to a double layer (bilayer) of phospholipids o Fluid = capable of flowing and easily changing shape o Mosaic = containing various components of different type Phospholipids are amphipathic – one side is polar, the other side is non polar. Describe the structure of a phospholipid. Describe the structure of the lipid bilayer. Selective Permeability Fluidity Affected by temperature Can be controlled o Fatty acid saturation o Cholesterol concentration Membrane Proteins Types o Integral/Transmembrane o Peripheral Structure/Orientation o Established by Endoplasmic Reticulum o Determined by type of amino acids at various points on the protein. o Very important for function of protein in the membrane Function o Transport o Enzymatic Activity o Signal Transduction o Intercellular Joining o Cell-Cell Recognition o Attachment to Cytoskeleton and Extracellular Matrix Movement across a plasma membrane Passive Transport: does not require external energy, moves down a concentration gradient. o Diffusion Movement of particles from high concentration to low concentration due to random motion. Moves toward dynamic equilibrium o Osmosis Passive transport of water from. . . Low solute concentration to high solute concentration. High water potential to low water potential Hypotonic solution to hypertonic solution o Facilitated Diffusion Movement of a substance from high concentration to low concentration (down the concentration gradient) through a membrane protein. Does not require energy Active Transport: does require energy, moves a substance up its concentration gradient from low concentration to high concentration. o Examples Sodium-Potassium Pump Proton Pump Cotransport o Couple down hill diffusion of one substance to up hill transport of another. o Incorporates both active and passive transport. Exocytosis o A substance is released to the exterior of a cell Endocytosis: A substance is taken in to a cell o Phagocytosis o Pinocytosis o Receptor mediated endocytosis Chapter 48 What is the role of transport and channel proteins in propagating signals along a neuron, producing an action potential, and forming/maintaining resting potential? Osmosis and Water Potential Osmosis: Diffusion of water across a selectively permeable membrane 1. From a region of low solute concentration to a region of high solute concentration. 2. From high water potential to low water potential. 1. From a region of low solute concentration to a region of high solute concentration. Hypertonic solution: Having a larger solute concentration than another solution. Hypotonic solution: Having a smaller solute concentration than another solution. Isotonic solution: Having the same solute concentration as another solution. If solutes are not allowed to pass through a membrane, water will move through the membrane from a hypotonic solution to a hypertonic solution. Always moving toward equilibrium—having equal solute concentrations on both sides of a membrane. 2. From high water potential to low water potential. The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure. Water Potential = Pressure Potential + Solute Potential Water moves from high water potential to low water potential Effect of solute on water potential o Zero solute: Ψs = 0 o Adding solute makes Ψs negative Effect of pressure on water potential o Atmospheric pressure: Ψp = 0 o Increase pressure: Ψp larger/more positive o Decrease pressure: Ψp smaller/more negative (Ψ = Ψp + Ψs)