Question

Which of the following is released during conversion of succinate to fumarate in TCA cycle ?

• A. CO2
• B. ATP
• C. H2O
• D. FADH2

Hint:

- Succinate Dehydrogenase is the only enzyme of the TCA cycle that is membrane-bound (part of the inner mitochondrial membrane), serving as a direct link between the Krebs cycle and the Electron Transport Chain.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The Tricarboxylic Acid (TCA) cycle, also known as the Krebs cycle or Citric Acid cycle, is a key metabolic pathway in aerobic respiration that oxidizes acetyl-CoA to produce carbon dioxide, energy (ATP/GTP), and reducing equivalents (NADH and \(FADH_2\)).

Step 2: Detailed Explanation:
Let us analyze the specific biochemical reaction involving the conversion of succinate to fumarate in the mitochondrial matrix:
- During this step, succinate is oxidized to fumarate by the enzyme succinate dehydrogenase (which is structurally bound to the inner mitochondrial membrane as Complex II of the electron transport chain).
- This reaction is a dehydrogenation reaction where two hydrogen atoms are removed from succinate.
- The coenzyme Flavin Adenine Dinucleotide (FAD) acts as the electron acceptor and is reduced to form \(FADH_2\) according to the following reaction:
\[ \text{Succinate} + \text{FAD} \xrightarrow{\text{Succinate Dehydrogenase}} \text{Fumarate} + \text{FADH}_2 \]
- No carbon dioxide (\(CO_2\)) is released, no water molecule is involved, and no ATP is directly generated during this specific step.
- The generated \(FADH_2\) enters the electron transport chain to produce approximately 1.5 ATP molecules.

Step 3: Final Answer:
The molecule released during this conversion is \(FADH_2\) (Option D).