Chapter_13

Chapter_13 - Chapter 13 Membrane Channels &...

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Unformatted text preview: Chapter 13 Membrane Channels & Pumps Active Transport uphill ATPase driven pumps Sodium-calcium exchanger Passive Transport downhill (facilitated diffusion) Ligand-gated (acetylcholine) Voltage-gated (Na+ & K+) Principles of Membrane Transport Lipophilic molecules can move through membrane by diffusion Polar molecules require a channel or pump Concentration gradients of polar molecules are associated with unfavorable free energy (entropy) Concentration gradients may need energy input to produce Concentration gradients can be a means of storing energy Quantification of Free Energy Stored at a Membrane To Transport species from side 1 to side 2 of a membrane: G = RT ln(c2/c1) = 2.303RTlog10(c2/c1) G = RT ln(c2/c1) + ZF V = 2.303RTlog10(c2/c1) + ZF V Where c1, c2 = concentration of side 1 & side 2 of membrane Z = electric charge , V = potential across membrane, F = faraday = 23.1 kcal/V-mol For c1 = 10-3 M, c2 = 10-1 M, G = + 2.7 kcal/Mol (unfavorable) Compare to ATP hydrolysis -12 Kcal/mol Transport of uncharged solute Transport of single charge Concentration gradient of 10 ~ free energy content of 59 mV gradient Ion Pumps Maintain Membrane Potentials N domain binds ATP P Accepts phosphoryl on Asp A (actuator) Ca+ ATPase in the SR: 0.1 M in cytosol, 1.5 mM in SRCa+ ATPase in the SR: 0....
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Chapter_13 - Chapter 13 Membrane Channels &...

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