Help with a membrane potential problem. Please solve for A and B and explain why

Question

Help with a membrane potential problem. Please solve for A and B and explain why/which values you used.

5. A. Assuming that the free-energy change for ATP hydrolysis under cellular conditions is about (inside negative) transmembrane potential, given the concentrations listed in the figure below. 3 Na Membrane potential Na K ATPase -50 to -70 mV ATP ADP P 2 K Cytosol [K+] 140 mM Na 12 mM Extracellular fluid CK 4 mM or blood plasma Nat] 45 mM B. Assuming that the ion concentrations did not change, at what transmembrane voltage would this pump stall?

Explanation / Answer

A. For Na+ pumping out against the gradient

Delta G = RT ln C (inside)/ C (Outside) + zFE

= 1.987 x 310 x ln 12/145 + 2.3 x 104 (-0.06)

= + 3.15 Kcal/mol

For K+ inside against the gradient

Delta G = 1.987 x 310 x ln 140/4 + 2.3 x 104 (-0.06)

= + 3.79 Kcal/mol

Total free energy change for the coupled process is

Delta G = deltaG(ATP) + deltaG(Na) + deltaG(K)

= -13.86 + 3.15 + 3.79

= -6.92 Kcal/mol

B. Cells accumulate an overall membrane potential which is a separation of charged particles in the form of Na+ and K+ ions. The resting potential of approx -70mV as this voltage maintains the ion gradients. The membrane potential is caused by a polarisation of ions.

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