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

Options

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

Answer

To solve the question of which amino acid is a precursor for thyroxine, adrenaline, and melanin, we can follow these steps:

### Step 1: Identify the amino acids listed
We need to consider the amino acids that are commonly known and their roles in the body. The options provided in the question are likely to include glycine, histidine, tryptophan, and tyrosine.

### Step 2: Analyze the functions of each amino acid
- **Glycine**: This amino acid is primarily involved in the formation of heme proteins but does not directly contribute to the synthesis of thyroxine, adrenaline, or melanin.

- **Histidine**: While histidine is important for various enzymatic functions and is present at the active sites of enzymes, it is not a precursor for the mentioned hormones or pigments.

- **Tryptophan**: This aromatic amino acid is involved in the production of serotonin and melatonin but does not serve as a precursor for thyroxine or adrenaline.

- **Tyrosine**: This is the key amino acid we are looking for. Tyrosine is a precursor for several important substances in the body, including:
- **Thyroxine**: A hormone produced by the thyroid gland that regulates metabolism.
- **Adrenaline (Epinephrine)**: A hormone produced by the adrenal glands that is involved in the body's fight-or-flight response.
- **Melanin**: The pigment responsible for the color of skin, hair, and eyes.

### Step 3: Conclusion
Based on the analysis, the amino acid that acts as a precursor for thyroxine, adrenaline, and melanin is **Tyrosine**.

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

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