With reference to glucose metabolism and cellular respiration, consider the following statements:
Statement 1: The conversion of succinate to fumarate in the TCA cycle is unique because it is the only step catalyzed by an enzyme embedded in the inner mitochondrial membrane and directly links the TCA cycle to the electron transport chain.
Statement 2: Oxidative phosphorylation is the only stage of cellular respiration where oxygen is directly consumed, and all ATP generated in this stage is produced by substrate-level phosphorylation.
Statement 3: In glycolysis, the enzyme phosphofructokinase-1 (PFK-1) is allosterically inhibited by high concentrations of ATP and citrate, making it a key regulatory point for both glycolysis and the TCA cycle.
Which of the statements given above are correct?

Correct option is B

The correct answer is (b) Statement 1 and Statement 3 only

Explanation:

• Statement 1 is correct: Succinate dehydrogenase is the enzyme for this step and acts as Complex II of the electron transport chain (ETC).
• Statement 2 is incorrect: While oxygen is the final electron acceptor in oxidative phosphorylation, ATP is produced by chemiosmosis (using ATP synthase), not substrate-level phosphorylation.
• Substrate-level phosphorylation occurs in glycolysis and the TCA cycle directly.
• Statement 3 is correct: PFK-1 is the rate-limiting enzyme of glycolysis; it is inhibited by high ATP (signaling high energy) and Citrate (linking it to TCA cycle activity).
• PFK-1 is activated by AMP and Fructose-2,6-bisphosphate.

Information Booster:

• The TCA Cycle occurs in the mitochondrial matrix, except for the succinate-to-fumarate step.
• The net yield of ATP from one molecule of glucose is approximately 30-32 ATP in eukaryotes.

Additional Knowledge:
All Statements are correct (Option a)

• Incorrect because Statement 2 misdefines the mechanism of ATP production in oxidative phosphorylation.

Statement 3 only (Option c)

• Incorrect because Statement 1 is also a well-established biochemical fact.

Statement 1 and Statement 2 only (Option d)

• Incorrect because Statement 2 is factually wrong regarding phosphorylation types.

So the correct answer is (b)