ADP + Pi <-----> ATP G = + 7 kcal/mole How long will this reaction take to reach

Question

ADP + Pi <-----> ATP G = + 7 kcal/mole

How long will this reaction take to reach equilibrium at 37 C and pH = 7.

(Mark the true statements. 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 100C.

Can't tell but it would be slower at 100C.

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 100C.

Can't tell but it would be slower at 100C.

Explanation / Answer

Ans. Note the following points-

I. To predict the direction of a reaction (and possible the time required for the equilibrium to be attained) the concertation of reactants (and/or products) must be provided.

By calculating reaction quotient, Q from given concentrations of reactants and products, we can predict the direction of reaction.

II. ATP synthesis from ADP and Pi is catalyzed by ATP synthase. So, without the enzyme, the synthesis of ATP from ADP and Pi is not feasible because of large positive dG.

Moreover, incubating the reaction mixture at 100.00C will denature the enzyme and there would be NO ATP synthesis.

III. ATP hydrolysis is spontaneous because of large negative free energy change. So, if there is only ATP or (ATP + ADP + Pi) in the reaction mixture, ATP undergoes spontaneous hydrolysis and equilibrium will be attained in relatively short time.

Conclusion: Correct option- A. Can’t predict.

Since the constitution of reaction mixture is NOT provided, the establishment of equilibrium can’t be predicted. For example, if there is only ADP and Pi in the reaction mixture, there would be no ATP synthesis without ATP synthase enzyme. Of, if there is ADP + Pi + ATP synthase in reaction mixture, incubating the reaction mixture would inactive the enzyme. If there is only ATP in reaction mixture, spontaneous ATP hydrolysis would lead to equilibrium establishment is short time.

So, among several options to be predicted, the correct one can NOT be predicted because the constitution of reaction mixture is NOT mentioned.

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