Question: 101: The number of time(s) decarboxylation of isocitrate occurs during single TCA cycle is :
(1) One
(2) Two
(3) Three
(4) Four
Answer: Option (2)
Explanation:
The tricarboxylic acid (TCA) cycle is a central metabolic pathway where acetyl-CoA is completely oxidised to carbon dioxide.
Isocitrate undergoes oxidative decarboxylation in the TCA cycle through enzyme-catalysed steps that result in the release of carbon dioxide.
First, isocitrate is converted into oxalosuccinate by the enzyme isocitrate dehydrogenase.
Oxalosuccinate is an unstable intermediate and immediately undergoes decarboxylation to form alpha-ketoglutarate with the release of one molecule of carbon dioxide.
Next, alpha-ketoglutarate undergoes another oxidative decarboxylation to form succinyl-CoA,
releasing the second molecule of carbon dioxide.
Thus, during one complete TCA cycle, decarboxylation reactions associated with isocitrate metabolism occur two times.
Therefore, the correct answer is Option (2).