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: Introduction: 
The task is to order the intermediate compounds in the Tricarboxylic Acid (TCA) cycle (Krebs cycle/citric acid cycle). 
 

Step 2: Process Overview: 
The TCA cycle releases stored energy in aerobic organisms. The sequence of the given compounds is: 
\[\begin{array}{rl} 1. & \text{Acetyl-CoA combines with Oxaloacetate to form (B) Citric Acid.} \\ 2. & \text{Citric acid is converted to (A) Isocitric Acid.} \\ 3. & \text{Isocitric acid is oxidized and decarboxylated, leading to other intermediates.} \\ 4. & \text{Succinate is oxidized to form (C) Fumaric Acid.} \\ 5. & \text{Fumaric acid is hydrated to form (D) Malic Acid.} \\ 6. & \text{Malic acid is oxidized back to Oxaloacetate, restarting the cycle.} \\ \end{array}\]

The correct chronological order is: Citric Acid \(\rightarrow\) Isocitric Acid \(\rightarrow\) Fumaric Acid \(\rightarrow\) Malic Acid. 
 

Step 3: Solution: 
The correct order in the TCA cycle is (B), (A), (C), (D).