Which of the following amino acids is essential for metabolism ?

Options

A. Serine
B. glycine
C. Phenylalanine
D. Aspartic acid

Answer

To determine which amino acid is essential for metabolism among the given options (serine, glycine, phenylalanine, and aspartic acid), we can follow these steps:

### Step-by-Step Solution:

1. **Understand Amino Acid Classification**:
- Amino acids are classified into three categories: essential, non-essential, and semi-essential.
- Essential amino acids cannot be synthesized by the body and must be obtained through diet.
- Non-essential amino acids can be synthesized by the body, so they do not need to be included in the diet.
- Semi-essential amino acids are usually not essential but may become essential under certain conditions (e.g., pregnancy, illness).

2. **List the Essential Amino Acids**:
- The essential amino acids include:
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Valine

3. **Evaluate Each Option**:
- **Serine**: Classified as a non-essential amino acid. It can be synthesized by the body.
- **Glycine**: Classified as a semi-essential amino acid. It is generally considered non-essential as the body can produce it.
- **Phenylalanine**: Classified as an essential amino acid. It must be obtained through the diet.
- **Aspartic Acid**: Classified as a non-essential amino acid. It can be synthesized by the body.

4. **Identify the Correct Answer**:
- Among the options provided, **phenylalanine** is the only essential amino acid required for metabolism.

### Conclusion:
The correct answer is **phenylalanine**.

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