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lecture notes for prelim 2

lecture notes for prelim 2 - Membrane Transport 15:09...

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Membrane Transport 15:09 Membrane Transport Reading: ECB 387-408 Which one of the following organisms will have the highest percentage of unsaturated fatty acid chains in their membranes? Antarctic fish o cold temperatures would make membrane less fluid, so increasing unsaturated fatty acids would help make it more fluid Desert iguana Human being Polar bear Thermophilic bacterium Lipid bilayers block the passage of most water-soluble molecules Transport proteins move water-soluble molecules across cell membranes (they are specific) If goes through many times, can form aqueous pore (multiple alpha helices) Membran transport proteins fall into two classes: Channels o Pores that can open and close o When open, ions can flow right through easily Transporters o Generally proteins that have binding sites for solutes they want to transport
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o Transition from one state to another usually Passive transport: uncharged molecules move down their concentration gradient For charged molecules, the membrane potential also plays a role in passive transport total force- sometimes called electrochemical gradient The glucose transporter mediates passive movement Has a binding site for glucose Flips back and forth- state A, state B Does it whether or not there is glucose
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Active transport uses energy to move molecules against their electrochemical gradients coupled- couple the uphill transport of one solute with the downhill transport of another ATP driven pump- couple uphill transport of a solute with hydrolysis of ATP light driven- couple uphill transport with the input of energy from light- in bacteria Both passive and active transport can be coupled Transporter that sends a single molecule through = uniport Moving two molecules through- both moving in same direction = symport “” in different directions = antiport can be active or passive The Na+ - K+ pump Move sodium out of cell, moves potassium into the cell
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Created large electrochemical Na+ gradient Lot of force trying to get Na+ into the cell Working with gradient Electrochemical gradient for K+ is quite small because it is working against the gradient The Na+ - K+ pump transports ions in cyclic manner pump flipping back and forth between two states- and is being regulated by phosphorylation Na+ stimulates phosphorylation K+ stimulates dephosphorylation
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Na + binds to pump on cytosolic side pump phosphorylates itself phosphorylation triggers conformational change, Na + ejected out of cell K + binds on extracellular side pump dephosphorylates pump returns to original conformation, K + ejected into cytosol Possible mechanism for glucose-Na+ coupled transporter two states- can flip back and forth between the two binding site for glucose is only available if Na+ binds if Na+ doesn’t bind, there is no glucose binding site glucose will bind to State A much more readily than B, because there is a loss less
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