Question

ADP + Pi <-----> ATP  ΔG = + 7 kcal/mole How long will this reaction take to reach equilibrium at 37˚ C and pH = 7. (There may be more than one correct answer.)

		Can't predict.
		Can't predict exactly but it will be fast.
		Can't predict exactly but it will be slow.
		Can't tell but it would be faster at 100˚C.
		Can't tell but it would be slower at 100˚C.

Answer 1

Correct answers are-

Can't predict

Can't tell but it would be faster at 100 degree Celsius.

ATP is a very unstable molecule and formation of ATP by phosphorylation of ADP is an exothermic process (+7kcal/mole). Without input of energy this conversion isn't possible. ADP is more stable than ATP. ATP tends to break down into ADP and Pi. So the reaction at 37 degree Celsius will be very slow. In biological systems, conversion of ADP to ATP by phosphorylation doesn't occur spontaneously and is always coupled to other exothermic processes. And as this reaction is endothermic so very high temperatures will facilitate the reaction. That's why reaction will be faster at 100°C than 37°C.