In considering active transport by Na+-K+-ATPase, 3 Na+ are pumped out of the ce

Question

In considering active transport by Na+-K+-ATPase, 3 Na+ are pumped out of the cell and 2 K+ are pumped in for each ATP that is hydrolyzed to ADP + Pi. Given a G for ATP hydrolysis of -10 kcal/mol, and that V is -60 mV (more electronegative inside), and that the pump typically maintains the internal Na+ at 10mM, external Na+ at 145 mM, internal K+ at 140 mM and external K+ at 5mM, what is the efficiency of the pump (i.e., what fraction of the energy available from ATP hydrolysis is used to drive transport)?

Explanation / Answer

The efficiency of the pump is the energy needs of the pump to move the ions. It is calculated as follows:

Energy required to pump Na+ ions:

Since Na+ is transported against concentration gradient, work must be done, and hence the free energy change is positive.

For K+, the free energy change is calculated as follows:

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