Determine the maximum concentration gradient | Quick Homework Help
At equilibrium, where DG=0, the equations can be rearranged to the more familiar form known as the Nernst equation:
V = 2.3 (R T/zF) log10 (Co/Ci)
For the questions below, assume that hydrolysis of ATP to ADP and Pi proceeds with a DG of -12 kcal/mole; that is, ATP hydrolysis can drive active transport with a DG of +12 kcal/mole. Assume that V is -60 mV
A. What is the maximum concentration gradient that can be achieved by the ATP-driven active transport into the cell of an uncharged molecule such as glucose, assuming that 1 ATP is hydrolyzed for each solute molecule that is transported.
B. What is the maximum concentration gradient that can be achieved by active transport of Ca2+ from the inside to the outside of the cell? Howr does this maximum compare with the actual concentration gradient observed in mammalian cells which have 10-4 mM inside of the cells and 1-2 mM outside of the cells?
C. Calculate how much energy it takes to drive the Na+-K* pump. This remark- able molecular device transports five ions for every molecule of ATP that is hydrolyzed: 3 Na+ out of the cell and 2 K+ into the cell. The pump typically maintains internal Na+ at 10 mM, external Na+ at 145 mM, internal K+ at 140 mM, and external K+ at 5 mM. We know that Na+ is transported against the membrane potential, whereas K+ is transported with it. (The DG for the overall reaction is equal to the sum of the DG values for transport of the individual ions.)
D. How efficient is the Na+-K+ pump? That is, what fraction of the energy available from ATP hydrolysis is used to drive transport?
