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

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.

Quizplus · Accepted Answer

Since the hydrolysis of ATP is exergonic and releases energy, the reverse reaction of forming ATP from ADP and inorganic phosphate would require an input of energy. Under cellular conditions where the free energy change for hydrolysis of ATP is more negative, the free energy change for the reverse reaction of ATP formation would be more positive. Therefore, the free energy change for the formation of ATP from ADP and inorganic phosphate under cellular conditions would be approximately +13 kcal/mol.

For the Hydrolysis of ATP to ADP + ᵢ