Which vitamin required for hydroxylation of proline-

**Core Concept**
Vitamin C is essential for the hydroxylation of proline and lysine residues in collagen, a critical step in the synthesis of collagen fibers. This process is crucial for the formation and maintenance of skin, bones, and connective tissue.

**Why the Correct Answer is Right**
Vitamin C acts as a co-factor for the enzyme prolyl hydroxylase, which catalyzes the hydroxylation of proline residues in collagen. This reaction is necessary for the stabilization of the collagen triple helix structure and its proper folding. Without sufficient vitamin C, collagen synthesis is impaired, leading to scurvy and other connective tissue disorders.

**Why Each Wrong Option is Incorrect**
**Option A:** Vitamin B12 is involved in the synthesis of methionine and the metabolism of fatty acids, but it is not directly involved in the hydroxylation of proline.
**Option B:** Vitamin D is essential for calcium absorption and bone health, but it is not directly involved in the hydroxylation of proline.
**Option C:** Vitamin K is necessary for blood clotting and bone health, but it is not directly involved in the hydroxylation of proline.

**Clinical Pearl / High-Yield Fact**
Vitamin C deficiency can lead to scurvy, a condition characterized by fatigue, malaise, and connective tissue disorders. Scurvy was a significant problem in sailors during long sea voyages, where fresh fruits and vegetables were scarce.

**Correct Answer:** C. Vitamin C.