Which of the following is not an essential amino acid?

Options

A. Lysine
B. Glysine
C. Phenylalanine
D. Valine

Answer

To determine which of the following is not an essential amino acid, we need to identify the essential amino acids and compare them with the options provided.

### 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. There are 9 essential amino acids that humans need to consume.

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

3. **Analyze the Options**:
The options given are:
1. Lysine
2. Glycine
3. Phenylalanine
4. Valine

4. **Identify Which Ones are Essential**:
- **Lysine**: Essential
- **Glycine**: Not essential (it can be synthesized by the body)
- **Phenylalanine**: Essential
- **Valine**: Essential

5. **Conclusion**:
Among the options provided, Glycine is the only amino acid that is not essential. Therefore, the answer to the question is **Glycine**.

### Final Answer:
**Glycine** is not an essential amino acid.

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