Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : The cataplerotic reactions helps to avoid the inappropriate build up of the citric acid cycle intermediates in the mitochondrion.
Reason R : The cataplerotic reactions replenish the citric acid cycle intermediates.
In light of the above statements, choose the correct answer from the options given below

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is NOT the correct explanation of A
• C. A is true but R is false
• D. A is false but R is true

Hint:

Anaplerotic = Add (Replenish).
Cataplerotic = Clear out (Remove).
Think of the TCA cycle as a busy roundabout; Anaplerosis is cars entering, Cataplerosis is cars exiting to reach their destination.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question tests the conceptual definitions of "Anaplerotic" versus "Cataplerotic" reactions in relation to the Citric Acid (TCA) cycle.

Step 2: Detailed Explanation:

• What is the TCA Cycle? The TCA cycle is "amphibolic," meaning it is involved in both breaking down fuel (catabolism) and providing precursors for synthesis (anabolism).

• Assertion A Analysis: Cataplerotic reactions are pathways that remove intermediates from the TCA cycle to be used for biosynthetic processes (e.g., Citrate for fatty acid synthesis, $\alpha$-KG for amino acids). By siphoning off these molecules, they prevent an excessive buildup that might stall the cycle. Thus, Assertion A is true.

• Reason R Analysis: Reactions that replenish or "fill up" the cycle intermediates are called anaplerotic reactions (e.g., Pyruvate carboxylase making Oxaloacetate). Cataplerotic reactions do the exact opposite. Therefore, Reason R is a false definition.

Step 3: Final Answer:
Assertion A correctly describes the function of cataplerosis, but Reason R incorrectly defines it as a replenishing process.