The Na+/K+-ATPase membrane protein "pumps" Na+ and K+-ions across a cell membrane. Na+ is pumped out of the cell and K+ is pumped into the cell.
a) At equilibrium at 310 K, the Na+ concentration outside the cell is 140 mM and the Na+ concentration inside the cell is 10 mM. What is the membrane voltage associated with the Na+ concentration gradient?
b) At equilibrium at 310 K, the K+ concentration outside the cell is 5 mM and the K+ concentration inside the cell is 70 mM. What is the membrane voltage associated with the K+ concentration gradient?
c) In the Na+/K+-ATPase membrane protein pumps 3 Na+ out of the cell for every 2 K+ into the cell. This not only produces the concentration gradient for K+ and Na+ ions but also generates the voltage difference (i.e. Δφ=φin - φout < 0). So, the voltages in (a) and (b) do not cancel each other... What is the total net voltage across the cell membrane, given Δφ= -70 mV?
d) How much free energy must be supplied from the ATP in order to achieve this membrane voltage?