Question

One reason that explains the need for the isomerization step in the citric acid cycle is that________

• citrate is a tertiary alcohol, which cannot be oxidized
• the substrate is inactive
• citrate is a β-keto acid and is unstable
• there are no enzymes that can catalyze this reaction

In the CAC reaction with the hydrolysis of succinyl-CoA,         

• the energy released is used to make GDP
• α-ketoglutarate is released
• the energy released is used to make GTP
• carbon dioxide is released

Answer 1

One reason that explains the need for the isomerization step in the citric acid cycle is that carbon dioxide is released

reason = in the first step (3c) pyruvate losses carbon dioxide by oxidatative decarboxylation , in the presence of enzyme pyruvate dehydrogenase . as a result a (2 c) acetyl moisty which interacts with coenzyme A producing acetyl co A . it further reacts with (4c ) oxaloacetate to form 6 carbon citrate this is followed by series of rearrangements  untill carbon eqivalent to pyruvate gets converted to carbon dioxide and to regenerate oxaloacetate to continue the cycle