Question

Arrange the following in the order of their occurance in TCA cycle
(A). Isocitric Acid
(B). Citric Acid
(C). Fumaric Acid
(D). Malic Acid
Choose the correct answer from the options given below:

• A. (B), (A), (C), (D).
• B. (A), (B), (D), (C).
• C. (B), (A), (D), (C).
• D. (C), (B), (D), (A).

Hint:

A helpful mnemonic for the TCA cycle intermediates is: "Citrate Is Krebs' Starting Substrate For Making Oxaloacetate". (Citrate, Isocitrate, \(\alpha\)-Ketoglutarate, Succinyl-CoA, Succinate, Fumarate, Malate, Oxaloacetate). This can help you quickly place the given compounds in the correct order.

Answer 1

The Correct Option is A

 

Step 1: Understanding the Concept: 
The question asks to arrange the given intermediate compounds in the correct sequence as they appear in the Tricarboxylic Acid (TCA) cycle, also known as the Krebs cycle or citric acid cycle. 
 

Step 2: Detailed Explanation: 
The TCA cycle is a series of chemical reactions used by all aerobic organisms to release stored energy. The sequence involving the given compounds is as follows: 
\[\begin{array}{rl} 1. & \text{The cycle begins when Acetyl-CoA combines with Oxaloacetate to form (B) Citric Acid.} \\ 2. & \text{Citric acid is then isomerized into its isomer, (A) Isocitric Acid.} \\ 3. & \text{Isocitric acid is then oxidized and decarboxylated, leading to a series of other intermediates (alpha-ketoglutarate, succinyl-CoA, succinate).} \\ 4. & \text{Succinate is oxidized to form (C) Fumaric Acid.} \\ 5. & \text{Fumaric acid is then hydrated to form (D) Malic Acid.} \\ 6. & \text{Finally, Malic acid is oxidized back to Oxaloacetate, allowing the cycle to begin again.} \\ \end{array}\]

Therefore, the correct chronological order for the given molecules is Citric Acid \(\rightarrow\) Isocitric Acid \(\rightarrow\) Fumaric Acid \(\rightarrow\) Malic Acid. 
 

Step 3: Final Answer: 
The correct order of occurrence in the TCA cycle is (B), (A), (C), (D).