membranes are made up of phospholipid molecules and proteins
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History of membrane model 1925 Gorter and Grendal cell membranes are two phospholipid bilayers
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1935 Davison and Danielli figured out where proteins fit in bilayer, accepted until early 1970's
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1972 Singer and Nicolson proteins are dispersed throughout phospholipids proteins have both hydrophilic and hydrophobic regions
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freeze fracture technique to look at bilayer membranes
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Membranes are fluidfluid mosaic model
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Membrane proteins tend to move sideways within the plasma membrane
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Integral proteins penetrate the hydrophobic core Transmembrane proteins go all the way through the membrane peripheral proteins not imbedded in bilayer at all loosely bound to surface
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structure of transmembrane protein
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functions of membrane proteins
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role of carbohydrates in membranes cell to cell recognition glycolipids glycoproteins carbohydrates on external side of membrane vary from species to species, within same species and even between cells
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synthesis of membrane components and their orientation on the resulting membrane
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Contractile vacuole
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Facilitated diffusion passive transport using diffusion and a transport protein no energy used for polar molecules and ions Uses: 1. Channel proteins pore that allows molecule to pass (hydrophilic passageways in proteins) Ex. aquaporins for water 2. ion channels open or close due to stimulus (electrical or chemical) Ex. gated channels
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Cystinuria disease of kidneys absence of carrier protein that transports cysteine and other amino acids across cell membranes in kidneys normal cells reabsorb these amino acids and put it into bloodstream abnormal cells develop stones of amino acids accumulate and crystalize
Active Transport uses energy to move solutes against a gradient ATP transfers terminal phosphate to a transport protein. causes protein to change its shape to move solute across membrane 1. sodiumpotassium pump generates a voltage across the membrane= electrogenic pump
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Ion pumps maintain Membrane potential membrane potential = voltage across the membrane (mV) 50 to 200 mV (minus sign = inside of cell is neg.) this favors passive transport of cations into the cell and anions out of the cell so: chemical force due to ion concentration gradient electrical force affects movement of ion due to membrane potential = electrochemical gradient if down gradient = passive if against gradient = active
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2. proton pump also an electrogenic pump transports hydrogen ions (protons) out of the cell used in ATP synthesis (cell respiration)
3. Cotransport uses ATP transport of a specific solute drives the active transport of other solutes driven by a concentration gradient
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Use of cotransport: diarrhea • patient given a solution of high glucose and salt. • taken up by transport proteins of intestinal cell membranes and passed into blood • increase in solutes of blood causes flow of water from the intestine into the blood = rehydration
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4. Bulk Transport for large molecules ex. proteins, polysaccharides a. Exocytosis secretion by fusing vesicles to cell membrane and expelling contents Ex. insulin excreted by pancreas this way neurotransmitters in neurons b. Endocytosis brings substances into the cell by forming new vesicles from cell membrane 1. phagocytosis if particulates 2. pinocytosis if liquids 3. receptormediated endocytosis if use binding sites use of ligands any molecule that binds specifically to receptor site of another molecule
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So:
How does the plasma membrane regulate cell activity?
