Which vitamins are involved in the metabolism of carbohydrates, fats, and proteins?

• A. Vitamin C and Vitamin E
• B. Riboflavin and niacin
• C. Biotin and pantothenic acid
• D. Vitamin A and Vitamin D

Answer: (C)

This question tests which vitamins provide essential cofactors that are central to metabolizing all three macronutrients. Pantothenic acid forms coenzyme A, a carrier for acetyl and acyl groups. CoA is the pivotal cofactor for turning carbohydrates into acetyl‑CoA, feeding acetyl units into the TCA cycle; it drives beta-oxidation of fats; and it participates in amino acid catabolism that feeds into acetyl‑CoA or other intermediates. Biotin acts as a coenzyme for carboxylases, enzymes that add CO2 to substrates—crucial steps in gluconeogenesis and in fatty acid synthesis, and also involved in metabolism of certain amino acids. Taken together, this pair provides the metabolic backbone that connects carbohydrate, fat, and protein metabolism.

Riboflavin and niacin are indeed important for energy metabolism through their redox cofactors (FAD and NAD+), but they don’t provide the central acetyl‑CoA and carboxylase functions that link all three macronutrient pathways as directly as pantothenic acid and biotin do. The other vitamins listed are more related to non-metabolic roles (antioxidant functions or vitamin-specific tissues).