If a lipid floppase can maintain a gradient of 500,000-fold in comparing the rat

Question

If a lipid floppase can maintain a gradient of 500,000-fold in comparing the ratio of phosphatidylcholine outside the plasma membrane to inside the plasma membrane (concentration greater outside than inside), what is the cost of bringing more phosphatidylcholine from the inner membrane to the outer membrane assuming the membrane potential is 50 mV (negative inside)? Phosphatidylcholine is zwitterionic with no net charge. Assume a physiologic temperature (310 K) and pH: R = 8.315 J/mol^*'K and Faraday's constant = 96, 480 J/V ^*mol + 33.8 kJ/mol -33.8 kJ/mol +14.7 kJ/mol +38.6 kJ/mol -38.6 kJ/mol

Explanation / Answer

G = - RT ln [S]in / [S]out + ZFVm
It is given in the question that phosphatidylcholine is zwitterionic with no net charge,
Z = 0 , hence the expression gets reduced to
G = - 8.315 * 310 ln [1/500000] = - (-33824.8599) J/mol = + 33.824 kJ/mol
First option seems to be the correct answer.

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