Q.48 Amino acid that serves as precursor for formation of the pigment responsible for human skin
color is
1. Tryptophan
2. Cholesterol
3. Tyrosine
4. Indoleamine
Title: Amino Acid Precursor for Human Skin Color Pigment: Tyrosine Explained (MCQ Solved)**
Tyrosine is the amino acid precursor for melanin, the pigment responsible for human skin color.
Correct Answer: 3. Tyrosine
Melanin synthesis begins in melanocytes where the enzyme tyrosinase converts tyrosine to DOPA and then dopaquinone, leading to eumelanin (brown-black) or pheomelanin (yellow-red). This pathway determines skin tone, hair color, and UV protection, with variations explaining diverse human pigmentation.
Melanin Biosynthesis Pathway
Tyrosine → L-DOPA (tyrosinase) → dopaquinone → melanin polymers. Tyrosinase is rate-limiting; defects cause albinism (OCA1). Phenylalanine converts to tyrosine via phenylalanine hydroxylase, linking diet to pigmentation.
Explanation of All Options
| Option | Role | Why Correct/Incorrect |
|---|---|---|
| 1. Tryptophan | Serotonin, niacin precursor. | Incorrect: Neurotransmitter synthesis; no role in melanogenesis. |
| 2. Cholesterol | Steroid hormone, membrane precursor. | Incorrect: Lipid; unrelated to pigment pathway. |
| 3. Tyrosine | Melanin direct precursor via tyrosinase. | Correct: First step in skin pigment formation. |
| 4. Indoleamine | Tryptophan metabolite (e.g., serotonin). | Incorrect: Neuroactive; not pigment-related. |
