Which amino acid is the precursor for epinephrine?

Options

A. Phenylalanine
B. Tyrosine
C. Histidine
D. Asparagine

Answer

To determine which amino acid is the precursor for epinephrine, we can follow these steps:

1. **Identify the Hormone**: We are looking for the precursor of epinephrine, which is a hormone involved in the body's response to stress and is also known as adrenaline.

2. **Understand the Biosynthesis Pathway**: The synthesis of epinephrine involves several steps, starting from an amino acid.

3. **Identify the Starting Amino Acid**: The primary amino acid that serves as the starting point for the synthesis of epinephrine is **tyrosine**.

4. **Outline the Conversion Process**:
- **Tyrosine** is converted to **DOPA** (dihydroxyphenylalanine) through the action of the enzyme tyrosine hydroxylase.
- **DOPA** is then converted to **dopamine**.
- **Dopamine** is further converted to **norepinephrine** (noradrenaline).
- Finally, **norepinephrine** is converted to **epinephrine** (adrenaline) through the action of the enzyme phenylethanolamine N-methyltransferase (PNMT).

5. **Conclusion**: Based on the biosynthesis pathway, we conclude that **tyrosine** is the precursor amino acid for epinephrine.

Therefore, the answer is **tyrosine**.