MCB130lectures4,5 - MCB130 R Schekman Transport of Small...

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MCB130 Lectures 4, 5 R. Schekman Transport of Small Molecules A. Function and types of permease 1. Permeases govern: ionic composition of cells and organelles; membrane potential; nutrient (sugar, amino acid) concentration. 2. Some permeases act to facilitate diffusion. Specific channel which allows a solute to equilibrate on two sides of membrane. 3. Other permeases engage in active transport. Energy-dependent transport of a solute against a concentration gradient. B. Sodium-potassium ATPase 1. Pump necessary to maintain proper ion balance in animal cell. a. For every ATP hydrolyzed, 3 Na + pumped out, 2 K + pumped in. b. Since unequal number of ions pumped, ATPase generates electrical current - electrogenic pump. 2. ATPase action requires Na + and Mg +2 a. Vanadate inhibits ATPase active site on cytoplasmic surface of membrane. 3. Pump is phosphorylated as enzyme intermediate a. Oubain binds on external surface of membrane b. Oubain inhibits dephosphorylation of P-enzyme formed in presence of Na + and Mg +2 4.
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