Which of the following amino acids is precursor of thyroxine, adrenaline and melanin?

Options

A. Tyrosine
B. Tryptophan
C. Histidine
D. Glycine

Answer

To determine which amino acid is the precursor of thyroxine, adrenaline, and melanin, we can follow these steps:

### Step 1: Identify the hormones
- **Thyroxine**: A hormone produced by the thyroid gland that regulates metabolism.
- **Adrenaline**: Also known as epinephrine, it is a hormone produced by the adrenal glands that helps the body respond to stress.
- **Melanin**: A pigment responsible for the color of skin, hair, and eyes.

### Step 2: Review the amino acids mentioned
- **Glycine**: Involved in the formation of heme, which is part of hemoglobin.
- **Histidine**: Plays a role in the active sites of certain enzymes.
- **Tryptophan**: Important for the formation of the plant hormone indole acetic acid and vitamin nicotinamide.
- **Tyrosine**: Precursor for several hormones and pigments.

### Step 3: Analyze the functions of the amino acids
- Glycine does not relate to the hormones in question.
- Histidine is not involved in the production of these hormones.
- Tryptophan is important for other substances but not for thyroxine, adrenaline, or melanin.
- Tyrosine is known to be a precursor for thyroxine, adrenaline, and melanin.

### Step 4: Conclusion
Based on the analysis, the amino acid that serves as a precursor for thyroxine, adrenaline, and melanin is **Tyrosine**.

### Final Answer
The correct answer is **Tyrosine**.

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