Question

For the nerve cell - part, what is the maximum number of potassium ions that can be pumped inward by the hydrolysis of one ATP molecule if the ATP/ADP ratio in the cell is 5.1 and the inorganic phosphate concentration is 10 mM? (Assume Î"G = -7.3 kcal/mol for ATP hydrolysis.) Express your answer as an integer.

a) 1
b) 2
c) 3
d) 4

Answer 1

The hydrolysis of one ATP molecule releases 7.3 kcal/mol of energy, and moving one sodium ion requires 2.1 kcal/mol. Therefore, one ATP molecule can move a maximum of 3 sodium ions across the membrane.

Step-by-step explanation:

The sodium-potassium pump is an essential mechanism in nerve cells that maintains the electrochemical gradient across the cell membrane. To determine the number of sodium ions one ATP molecule can move across the membrane, you need to compare the amount of energy released from ATP hydrolysis to the energy required to move each sodium ion.

ATP hydrolysis releases 7.3 kcal/mol of energy, and it takes 2.1 kcal/mol of energy to move one sodium ion. Therefore, if you divide the total energy released by the energy required per ion, you get:

7.3 kcal/mol / 2.1 kcal/mol/ion = 3.476 ions

Since you cannot move a fraction of an ion, the maximum number of sodium ions that can be moved by the hydrolysis of one ATP molecule is 3.