Lecture 2 - 1 BIO 317 Principles of Cellular Signaling...

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Unformatted text preview: 1 BIO 317 Principles of Cellular Signaling Lecture 2 Relative Permeability of Lipid Bilayer Permeability coefFcients (cm/sec) 2 Membrane Transport Cells need to transport specifc water-soluble molecules across the plasma membrane Ingest essential nutrients Excrete waste products Regulate intracellular ion concentrations How? Membrane Transport Proteins: Carrier Proteins Channel Proteins Membrane Transport Proteins 3 Passive Transport (Diffusion) Channel proteins create aqueous pores through the plasma membrane A solute diffuses through the aqueous pore down its concentration gradient The driving force is the concentration gradient of the solute Note, if a solute carries a net charge, then both the concentration gradient and the membrane potential will inFuence passive transport and Need to consider the electrochemical gradient (the combined effect of the concentration and electrical gradients) Carrier Protein-Mediated Passive (Facilitated) Transport Carrier protein has specic binding site(s) for substrate Carrier protein transfers substrate by undergoing reversible conformational changes The driving force is the concentration gradient of the solute Exhibits saturation kinetics (V max ) 4 Carrier Protein-Mediated Active Transport Example of Coupled Carrier Transport (secondary active transport) Glucose / Na + co-transport Carrier proteins oscillates between conformational states A and B alternately exposing binding sites to extracellular space and cytosol. Binding of Na + and glucose is cooperative - binding of Na + increases afFnity for glucose. The driving force is the electrochemical gradient of Na + ....
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Lecture 2 - 1 BIO 317 Principles of Cellular Signaling...

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