**Question:** Vitamin synthesised from amino acid is

A. Vitamin B12
B. Vitamin C
C. Vitamin D
D. Vitamin E

**Core Concept:** Vitamins are essential nutrients required by the body for various physiological processes but cannot be synthesized internally. Some vitamins, like B12, are synthesized from amino acids.

**Correct Answer: A. Vitamin B12**

Vitamin B12 is synthesized from the amino acid L-Methionine via a series of enzymatic reactions in the liver. It plays a crucial role in various biological processes, including DNA synthesis, myelin formation, and red blood cell production.

**Why the Correct Answer is Right:** Vitamin B12 is synthesized by the liver from L-Methionine through a series of enzymatic reactions. These reactions involve the enzyme methionine adenosyltransferase, which converts L-Methionine into S-Adenosylmethionine (SAMe). SAMe acts as a methyl group donor in various biological processes, including DNA synthesis, myelin formation, and red blood cell production.

**Why Each Wrong Option is Incorrect:**

**B. Vitamin C (Option B)** is synthesized from glucose and not amino acids. It acts as an antioxidant and is involved in collagen synthesis.

**C. Vitamin D (Option C)** is synthesized in the skin upon exposure to sunlight and is involved in calcium absorption and bone health. It is not directly related to amino acids.

**D. Vitamin E (Option D)** is synthesized from fatty acids and is involved in antioxidant defense and membrane structure. It is not directly related to amino acids.

**Clinical Pearl:** Understanding vitamin synthesis pathways is essential for clinical practice as it highlights the importance of a balanced diet and proper nutrition for maintaining overall health.

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To summarize, vitamin B12 is synthesized from the amino acid L-Methionine, and understanding this process emphasizes the significance of a balanced diet and proper nutrition for optimal health.