For the hydrolysis of ATP to ADP + ℗i, the free-energy change is -7.3 kcal/mol under standard conditions (1 M concentration of both reactants and products). In the cellular environment, however, the free-energy change is about -13 kcal/mol. What can we conclude about the free-energy change for the formation of ATP from ADP and ℗i under cellular conditions?
A) It is +7.3 kcal/mol.
B) It is less than +7.3 kcal/mol.
C) It is about +13 kcal/mol.
D) It is greater than +13 kcal/mol.
E) The information given is insufficient to deduce the free-energy change.

Question

Quizplus · Accepted Answer

The free-energy change for the hydrolysis of ATP is -7.3 kcal/mol under standard conditions, but the actual free-energy change under cellular conditions is about -13 kcal/mol. This indicates that the hydrolysis of ATP is more favorable under cellular conditions. Therefore, the reverse reaction, the formation of ATP from ADP and ℗i, is less favorable under cellular conditions. Since the free-energy change for this reaction is the negative of the free-energy change for the hydrolysis of ATP, it must be about +13 kcal/mol. Therefore, the correct answer is C (it is about +13 kcal/mol).

For the Hydrolysis of ATP to ADP + ℗I, the Free-Energy