Question

The dietary precursor of coenzyme A is

• A. Pantothenic acid
• B. Tocopherol
• C. Folate
• D. Thiamine

Hint:

The word "pantothenic" comes from the Greek "pantothen," meaning "from everywhere," reflecting its widespread occurrence in almost all dietary food sources.
Deficiency of this vitamin is therefore extremely rare.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Coenzyme A (CoA) is an essential cofactor required for the metabolism of fatty acids, carbohydrates, and amino acids.
It serves as an acyl group carrier in many biochemical reactions.
Detailed Explanation:
- Coenzyme A is synthesized in cells through a multi-step pathway starting from the water-soluble B-vitamin pantothenic acid (Vitamin $\text{B}_5$).
- The pathway involves:
1. Phosphorylation of pantothenic acid by pantothenate kinase to form 4'-phosphopantothenate.
2. Condensation with cysteine (supplying the reactive sulfhydryl group).
3. Decarboxylation to yield 4'-phosphopantetheine.
4. Adenylation and final phosphorylation to yield Coenzyme A.
- The active thiol group ($-\text{SH}$) at the end of the cysteamine moiety of CoA is what forms high-energy thioester bonds with acyl groups (such as in acetyl-CoA).
- Other options are precursors to different coenzymes:
- Tocopherol (Vitamin E) is a lipid-soluble antioxidant.
- Folate (Vitamin $\text{B}_9$) is the precursor to tetrahydrofolate (THF).
- Thiamine (Vitamin $\text{B}_1$) is the precursor to thiamine pyrophosphate (TPP).

Step 2: Final Answer:
Pantothenic acid is the dietary precursor of Coenzyme A. This corresponds to option (A).