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Transcript
Membrane Structure and Function Topic 3 Plasma Membrane Functions Maintain a high concentration of materials in the cell. Keep harmful materials out. Control the movement of materials into and out of the cell. Let the cell sense its environment. Membrane Structure Phospholipid bilayer Amphipathic “liquid-crystal” properties/behavior allow for constant movement of HC tails The Plasma Membrane is Semipermeable Davson-Danielli vs. Fluid Mosaic Membrane Characteristics “self-sealing” Flexible Tend to form vesicles (ENDOCYTOSIS) Tend to fuse w/ other bilayers (EXOCYTOSIS) LIPID MOBILITY http://www.d.umn.edu/~sdowning/Membranes/phospholipidlat eralmovanim.html http://www.d.umn.edu/~sdowning/Membranes/phospholipidrotation alanim.html Relationships w/ other intracellular membranes Nuclear Memb. Rough ER vesicles Golgi Bodies lysosomes & vacuoles vesicles cell memb MEMBRANE PROTEINS Integral Proteins: Anchored into membrane Transmembrane proteins Peripheral Proteins no anchoring to membrane often bound to exposed regions of integral proteins PROTEIN MOBILITY http://www.d.umn.edu/~sdowning/Membra nes/proteinmobilityanim.html Proteins Are Critical to Membrane Function Membrane Protein Functions Cell Adhesion Communication Channels Transport Channels Signal Receptors btwn. Ext/Int cell Attachment Sites Pumps Enzymes Peripheral Integral Integral Integral Peripheral Integral Both Protein Signaling http://www.d.umn.edu/~sdowning/Membranes/signalinga nim.html Membrane Components Phospholipids Proteins (peripheral and integral) Cholesterol Carbohydrates The Plasma Membrane – Gateway to the Cell MOVEMENT ACROSS THE CELL MEMBRANE Transport Processes - Diffusion Solutes move down a concentration gradient until they are evenly distributed. This is diffusion. Another way of saying this is that solutes move from a region of higher concentration to a region of lower concentration until there is no difference in concentration. Methods of Movement PASSIVE TRANSPORT DIFFUSION SIMPLE DIFFUSION OSMOSIS FACILITATED DIFFUSION Three Forms of Transport Across the Membrane ACTIVE TRANSPORT PUMPS EXOCYTOSIS ENDOCYTOSIS PHAGOCYTOSIS PINOCYTOSIS RECEPTOR-MEDIATED DIFFUSION Cell obtains / releases substances by taking advantage of natural properties of movement (kinetic E)! Diffusion is… NET movement of mcls from [ ] [ ] Down the [ ] gradient : . NO Energy required. Rate of Diffusion influenced by: Size / shape of molecules moving Electrical charges across membrane Temperature ( = movement, :. Diffusion ) Substances diffuse down their own [ ] gradient… NOT affected by [ ] gradient of other substances !! Diffusion continues until… Dynamic Equilibrium is reached! OSMOSIS Diffusion of water across the semi-permeable plasma membrane. Water moves down its own [ ] gradient. * Zones of Hydration Spheres of Hydration Osmotic Pressure tendency of water to move into a solution by osmosis. High [solute] = low [water] High Osmotic Pressure Comparing Solutions: HYPOTONIC : refers to the less concentrated (more dilute) of two solutions. HYPERTONIC : refers to the more concentrated (less dilute) of two solutions. If a cell is placed in a hypotonic solution, the cell will…. S W E L L and B U R S T !! Turgidity issues… If a cell is placed in a hypertonic solution, the cell will… S H R I N (CRENATION) K ! ISOTONIC : refers to two solutions where there is no net movement of water between the two. a cell is placed in an isotonic solution, there will be…. no net movement of water into / out of the cell. The Problem of Osmotic Pressure What’s the risk? How can osmotic pressure be minimized? Live in an isotonic enviroment Contractile vacuoles plasmolysis Marine invertebrates Human RBC’s Unicellular protists Plant cells Contractile Vacuoles Plasmolysis… Cell Wall Action Transport Problems ? CYSTIC FIBROSIS LIDDLE’S SYNDROME