1-24-08 - 1-24-08 Chapter 5 Membranes Cell membranes outer...

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Unformatted text preview: 1-24-08 Chapter 5 Membranes Cell membranes outer membrane is plasma membrane o Structure composed of lipid bi-layer with proteins embedded "fluid mosaic model" o Function regulates movement in and out of the cell Separates cell components "gate keeper" Movement across membranes o Diffusion Net movement of molecules from high to low concentration (high to low energy) until evenly distributed in a state of dynamic equilibrium Effective only over short distances Passive (no energy) o Facilitated Diffusion Requires a carrier protein in membrane, but no energy high to low o Osmosis Diffusion of water across a selectively permeable membrane From high to low concentration until evenly distributed in state of dynamic equilibrium Effects of osmosis if cell is placed in three different solutions Hyperosmotic a solution with a higher concentration of solute compared to another solution o Cell loses water and shrinks (crenation) Hypo-osmotic a solution with a lower concentration of solute compared to another solution o Cell gains water and expands (lyses) Iso-osmotic a solution with same solute concentration compared to another solution o Cell neither gains nor loses water o Active transport Carrier molecules move molecules across a membrane against a concentration gradient with an energy expenditure (ATP) "carrier molecule" in membrane (pump) Sodium potassium pump ATPase pump o Exocytosis "outside cells" Process of exporting large molecules from a cell by fusion of vesicles with the plasma membrane (requires energy) ...
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