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biology_notes_test_2[1] - TEST 2 Chapter 5 Biological...

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TEST 2 Chapter 5 – Biological Membranes -membranes are exceedingly thin -egg only 2 molecules thick Plasma Membrane -phospholipids (primarily) bilayer -proteins w/ in membrane Hydrophyllic on outside (heads) Hydrophobic on inside (tails) 1972 – Fluid Mosaic Model (structure of p.m.) – artistic description of association of proteins w/ bi-layer ; proteins stuck in p.m. (many purposes, also mobile) Bilayer behaves like a liquid crystal (from orderly arrangement of liquid molecules, like liquid b/c each phospholipid not attached..and constantly in motion) -very capable of moving around b/c hydrophyllic & hydrophobic All proteins in 2 main categories: a. proteins that extend part way through the bi-layer – integral proteins b. those that don’t extend into the bi-layer at all – peripheral proteins (would not disturb p.m. if removed) c. trans-membrane proteins – proteins that extend all the way through; stable; often asymmetrical - every protein that a cell makes for cell or environment is made in the Rough E.R. - if not extended through…a floating ribosome could have possibly made it MEMBRANE PROTEINS important for : 1. membrane transport 2. receptor cites 3. holding cells together 4. as enzymes (making things happen) Permeability – what substances can pass through the membrane -PERMEABLE to -anything nonpolar (O═O) - anything hydrophobic ex. hydrocarbons (C═O═C) (H2) (N2) -water must move through proteins because polarity will not let it through the bi- layer
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-NONPERMEABLE to: - anything charged (amino acids, glucose) - anything polar In order for a cell to do work, it needs the raw materials regulated by the “selectively permeable” plasma membrane (not semi b/c that means ½) Proteins are very impt. in deciding permeability and transport MOVEMENT OF MATERIALS FROM OUTSIDE-IN: (depends on what’s supplying energy) a. passive – cell does not expend energy (molecular motion does) b active – energy comes from cell itself Brownian motion- pollen grains jiggling under microscope; 2 water molecules constantly bombarding it; causes slight vibration Maximum disorder (Entropy ) – (maximum stability ) even distribution.. like salt completely dissolved in water Vs. Maximum order.. when stationary right after applying solute to solvent Diffusion – movement from higher to lower concentration; used in Passive transport; in order to occur, there must be a concentration gradient ( a difference in 2 concentrations.. high/low) - if both concentrations move through gradient – permeable - if one does – selectively permeable osmosis – when a solvent (water) diffuses through a membrane dialysis – diffusion of a solute Differences in osmotic pressure: -Hypertonic—more solutes and less solvent surrounding -isotonic—equal solute concentration -Hypotonic—less solutes and more solvent surrounding Osmotic pressure – the tendency of water to move into a solution by diffusion IT IS A PULL Water diffuses in the solute concentration until PUSH – hydrostatic pressure – of the weight of water pressure = osmotic pressure
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