Calculate the free energy for transporting Ca^2+ across a membrane from a concen

Question

Calculate the free energy for transporting Ca^2+ across a membrane from a concentration of 10.0 mM side 1) to a concentration of 1.00 mM (on side 2). The temperature is 25 degree C and the membrane potential delta psi is 0.0 V. The Faraday constant is 96.5 kJ middot V^-1 middot mol^-1 and the gas constant is 8.314 times 10^-3 kJ middot mol^-1 middot K^-1. Calculate the free energy for transporting Ca^2+ across a membrane in part A. when the membrane potential is +0.100 V (more positive on side 2 than on side 1). Which transport is more favorable, A. or B.? is more favorable is more favorable A. and B. are equally favorable

Explanation / Answer

A.

Free energy dG

dG = -RTlnK

Taking values from above,

dG = -8.314 x 298/2 x 96500 ln(1/10)

      = 0.02956 kJ/mol

B. Free energy change when membrane potential = +0.100 V

dG = -2 x 96500 x 0.1 + 0.02956

      = 193 kJ/mol

C. Favorable transport here would be,

B, is more favorable

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