Question

Which of the following reactions would require the hydrolysis of three ATP molecules (?G = -7.3 kCal) for it to occur?

A) A reaction that has a ?G = -8 kCal.
B) A reaction that has a ?G = +39 kCal.
C) A reaction that has a ?G = -39 kCal.
D) A reaction that has a ?G = +24 kCal.

Answer 1

None of the reaction options presented would be driven by the hydrolysis of three ATP molecules, but the closest option is Reaction D with a ΔG = +24 kCal, which would require the hydrolysis of four ATP molecules.

Step-by-step explanation:

The reaction that would require the hydrolysis of three ATP molecules to occur is the one with a ΔG = +39 kCal. This is because the hydrolysis of one ATP molecule releases 7.3 kCal of energy. To provide the energy needed for a +39 kCal reaction, it would take approximately the energy from the hydrolysis of five ATP molecules (5 x 7.3 kCal = 36.5 kCal), but since you cannot hydrolyze a partial ATP molecule, you would need to hydrolyze six ATP molecules to provide at least 39 kCal of energy, which exceeds the required ΔG of +39 kCal.

Therefore, to answer the initial question, none of the reactions listed would be accurately driven by just the hydrolysis of three ATP molecules, as the closest option (D) requires the hydrolysis of at least six ATP molecules.