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

The hydrolysis of ATP is an exergonic reaction, meaning that it releases energy. The fact that the free energy change for this reaction is greater (-13 kcal/mol) in the cellular environment than under standard conditions (-7.3 kcal/mol) suggests that the concentration of reactants and/or products is different in the cellular environment, causing the reaction to have a greater tendency to release energy. Therefore, the reverse reaction, the formation of ATP from ADP and inorganic phosphate, would have a positive free energy change under cellular conditions. The only answer choice that reflects a positive free energy change is C, about +13 kcal/mol.

For the Hydrolysis of ATP to ADP + ᵢ