Correct option is D
To determine the correct combination of statements regarding the conversion of pyruvate to acetyl-CoA, let's analyze each statement carefully.
Statement A: Oxidation of pyruvate to acetyl-CoA is reversible. (Incorrect)
- The conversion of pyruvate to acetyl-CoA by the pyruvate dehydrogenase complex (PDC) is irreversible.
- This is a one-way oxidative decarboxylation reaction that commits pyruvate to the TCA cycle or other pathways.
- Thus, statement A is incorrect.
Statement B: Pyruvate is transported into the mitochondrion by a transporter. (Correct)
- Pyruvate, generated in the cytoplasm through glycolysis, must enter the mitochondria for further metabolism.
- This transport is facilitated by the mitochondrial pyruvate carrier (MPC).
- Thus, statement B is correct.
Statement C: Pyruvate is carboxylated by pyruvate dehydrogenase. (Incorrect)
- Pyruvate dehydrogenase (PDH) catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA, not carboxylation.
- Pyruvate carboxylase, not pyruvate dehydrogenase, is responsible for carboxylation, which converts pyruvate to oxaloacetate (OAA).
- Thus, statement C is incorrect.
Statement D: Acetyl lipoamide reacts with coenzyme A to form acetyl-CoA. (Correct)
- In the pyruvate dehydrogenase complex (PDC), lipoamide acts as a swinging arm that transfers the acetyl group to coenzyme A (CoA).
- Thus, statement D is correct.
Statement E: The flavoprotein, dihydrolipoyl dehydrogenase, containing flavin adenine dinucleotide (FAD), is involved in the conversion of pyruvate to acetyl-CoA. (Correct)
- Dihydrolipoyl dehydrogenase (E3 subunit of PDC) contains FAD and catalyzes the regeneration of oxidized lipoamide.
- FAD is crucial for electron transfer in this reaction.
- Thus, statement E is correct.
Correct Answer:
(4) B, D, and E
