Essential amino acid is

Options

A. PhenyL alanine
B. Glycine
C. Aspartic acid
D. Serine

Answer

To determine which of the given amino acids is an essential amino acid, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Essential Amino Acids**:
Essential amino acids are those that cannot be synthesized by the body and must be obtained through diet. In contrast, non-essential amino acids can be produced by the body.

2. **Analyze the Given Options**:
The options provided are:
- A) Phenylalanine
- B) D-Glycine
- C) Aspartic Acid
- D) D-Serine

3. **Identify Each Amino Acid**:
- **Phenylalanine**: This is an essential amino acid. It must be obtained from food sources.
- **D-Glycine**: Glycine is a non-essential amino acid, as the body can produce it.
- **Aspartic Acid**: This is also a non-essential amino acid, as it can be synthesized by the body.
- **D-Serine**: Similar to glycine and aspartic acid, serine is a non-essential amino acid.

4. **Conclusion**:
Since phenylalanine is the only amino acid in the list that is classified as essential, the correct answer is:
- **Option A: Phenylalanine**.

### Final Answer:
The essential amino acid is **Phenylalanine** (Option A).

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