Which reactions in the citric acid cycle are irreversible under physiological conditions, and for each of...

Which reactions in the citric acid cycle are irreversible under physiological conditions, and for each of these reactions, explain why the reaction is irreversible.

Expert Solution

Solution :

There are three irreversible steps in citric acid cycle. These three steps are : citrate synthase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase.

1) The first reaction of citric acid cycle is citrate synthesis. It is synthesized by the condensation of acetyl CoA and oxalo-acetate. This step has highly negative ΔG value, which confirms the irreversibility of reaction.

2) In the third reaction of the citric acid cycle, isocitrate is converted to alpha-ketoglutarate by means of isocitrate dehydrogenase. This particular reaction posses highly negative ΔG value, thus it is considered as irreversible.

3) In the fourth reaction of citric acid cycle, the oxidation of alpha-ketoglutarate take place which is converted into succinyl-CoA with the help of alpha-ketoglutarate dehydrogenase enzyme. This step is highly energetic reaction and posses negative value of ΔG, hence it is also irreversible.

queen_honey_blossom answered 11 months ago

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