Which of the following vitamins serves as a hormone precursor
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Active Vitamin D (Calcitriol) is functionally a steroid hormone because it is synthesized in one organ (skin/kidneys), transported through the blood, and binds to nuclear receptors to regulate gene transcription.
Step 1: Understanding the Concept:
Vitamins are organic compounds required in small quantities for various metabolic functions. Some vitamins undergo metabolic conversions to yield active compounds that function as hormones. Step 2: Detailed Explanation:
Let us analyze the metabolic roles of the listed vitamins:
Vitamin D is synthesized in the skin from cholesterol derivatives upon exposure to solar UV radiation, or absorbed through the diet.
It is biologically inactive in this raw form and must undergo two successive hydroxylation steps:
1. First in the liver to form calcidiol [\(25(OH)D\)].
2. Then in the kidneys to form the biologically active form, calcitriol [\(1,25(OH)_2D\)].
Calcitriol behaves biochemically as a hormone. It binds to specific intracellular Vitamin D Receptors (VDR) in target tissues (such as the intestines and bones) to regulate gene expression, calcium absorption, and bone mineralization. Thus, Vitamin D serves as a hormone precursor.
Vitamin A, C, and K: Vitamin A is a precursor to retinal (vision) and retinoic acid. Vitamin C is an antioxidant and cofactor for collagen synthesis. Vitamin K is a cofactor for enzymes involved in the carboxylation of blood clotting factors. None of these function primarily as hormone precursors in the same classic manner as Vitamin D.
Therefore, Vitamin D is the vitamin that serves as a hormone precursor. Step 2: Final Answer:
The correct option is (C).
