Question

The anhydride formed between a carboxylic acid and a phosphate (Figure Q369A) is a high-energy intermediate for some reactions in which ATP is the energy source. Arsenate can also be incorporated into a similar high-energy intermediate in place of the phosphate (Figure Q3-69B). Figure Q3-69C shows the reaction profiles for the hydrolysis of these two high-energy intermediates. What is the effect of substituting arsenate for phosphate in this reaction?

(A) It forms a high-energy intermediate of lower energy.
(B) It forms a high-energy intermediate of the same energy.
(C) It decreases the stability of the high-energy intermediate.
(D) It increases the stability of the high-energy intermediate

Answer 1

Substituting arsenate for phosphate decreases the stability of the high-energy intermediate, causing the reaction to release energy more rapidly and reducing the overall energy output.

Step-by-step explanation:

The substitution of arsenate for phosphate in the high-energy intermediate affects the reaction by decreasing the stability of the high-energy intermediate.

In biological processes, ATP acts as a high-energy intermediate, with phosphoanhydride bonds that store energy.

The hydrolysis of ATP, where these bonds are broken, releases a significant amount of energy.

Arsenate resembles phosphate structurally, but forms less stable intermediates that can more readily break apart, thereby releasing the stored energy more rapidly and decreasing the overall energy output of the reaction.

This is because arsenate hydrolysis products are more prone to rapid decomposition compared to the more stable phosphate hydrolysis products.