Question

Which of the following vitamins is required for the formation of prothrombin and blood clotting?

• A. Retinol
• B. 1,25‐dihydroxycholecalciferol
• C. Menaquinone
• D. Alpha tocoperol

Hint:

Sweet clover poisoning in cattle is caused by dicumarol (a vitamin K antagonist), which inhibits vitamin K recycling.
This prevents the activation of prothrombin and other clotting factors, leading to fatal internal hemorrhaging.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Blood coagulation is a complex cascade of enzymatic reactions that forms a stable fibrin clot to prevent blood loss after vascular injury.
Several key clotting factors in this cascade require post-translational modification to become biologically active, a process that requires a specific fat-soluble vitamin.

Step 2: Detailed Explanation:
Vitamin K is an essential cofactor for the enzyme gamma-glutamyl carboxylase.
This enzyme adds carboxyl groups to glutamic acid residues on specific clotting factors, including Prothrombin (Factor II), Factor VII, Factor IX, and Factor X.
This carboxylation allows these proteins to bind calcium ions (\(\text{Ca}^{2+}\)) and attach to phospholipid membranes, which is necessary for their activation during coagulation.
Let us evaluate the listed vitamers:
- Menaquinone (C): Also known as Vitamin \(\text{K}_2\), this is the bacterial-origin form of Vitamin K. It is absorbed in the gut and functions as the cofactor for prothrombin activation and blood clotting.
- Retinol (A): Vitamin A, which is essential for vision, gene transcription, and epithelial integrity.
- 1,25-dihydroxycholecalciferol (B): Active Vitamin D, which regulates calcium and phosphorus homeostasis.
- Alpha-tocopherol (D): Vitamin E, which acts as a membrane-bound lipid antioxidant.
Therefore, Menaquinone is the vitamin required for prothrombin formation and blood clotting.

Step 3: Final Answer:
Menaquinone (Vitamin K) is required for the formation of prothrombin and blood clotting.