Can someone explain ATP reactions and their relationship to ∆G?

Question

The other day I was doing a practice Biology exam and got a little confused on these two questions. Is my line of thinking correct for these?

1. "T or F: If a reaction with a +3 ∆G is coupled with ATP hydrolysis, these reactions are overall spontaneous."

+3 ∆G means the reaction is not spontaneous, and I am assuming ATP hydrolysis will lower the free energy and make it spontaneous, right? But by how much?

2. "T or F: ATP can be coupled to an endergonic reaction, to drive the reaction forward."

ATP has stored up energy, right? So it will give that energy to the reaction which drives it forward? Or does this question mean that energy goes into a reaction that feeds the ATP?

Anyway, I hope someone can help me... I don't want you to do my homework or anything, I just need a little nudge.

Answer 1

Not sure, the overall reaction is may or may not spontaneous even if the ∆G produced by ATP hydrolysis is greater than reaction ∆G. This is because the reaction may have a very high activation energy in which energy provided by ATP hydrolysis may not be enough to overcome it.

ATP hydrolysis DOES NOT lower the free energy of the reaction, it only provides free energy for the reaction to proceed...


for the 2nd qn, does it mean ATP HYDROLYSIS can be coupled to an endergonic reaction. yes it can if the ∆G of the reaction is smaller (in absolute value) than ∆G generated by ATP hydrolysis

Saying that ATP has stored energy is ok...but I would say (i was taught) that ATP is unstable compared to ADP and phosphate, the products of its hydrolysis. Therefore, ATP would have a higher energy conformation than ADP and phosphate. And when ATP is hydrolysed, the energy is lost as free energy and some disorder heat energy to give lower energy ADP and phosphate...