Consider two reactions. Reaction 1 (P Q) has G = 2.3 kJ/mol. Reaction 2 (Q R) ha

Question

Consider two reactions. Reaction 1 (P Q) has G = 2.3 kJ/mol. Reaction 2 (Q R) has G = 12.3 kJ/mol. Which reaction is more likely to require coupling to ATP or the equivalent in order to be spontaneous under cellular conditions?

A.   Both reactions will require ATP or the equivalent to proceed under cellular conditions because both reactions are nonspontaneous and are the same distance from equilibrium in the cell.

B.   Reaction 2 (Q R). This reaction is nonspontaneous and operates far from equilibrium in the cell. It will not be able to proceed as written in the cell without coupling to a process with a large negative free energy change (such as ATP hydrolysis).

C.   Reaction 1 (P Q). This reaction is nonspontaneous and operates far from equilibrium in the cell. It will not be able to proceed as written without coupling it to a process with a large free energy change (such as ATP hydrolysis).

D.   Neither reaction will require ATP or the equivalent to become spontaneous in the cell. The fluctuations in the actual concentrations of substrates and products present in the cell will always allow a reaction that is nonspontaneous to become spontaneous eventually.

Explanation / Answer

Correct answer:- (A) both reaction will require ATP because both have positive Gibbs free energy and are non spontaneous reactions.

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