Which is an essential amino acid

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding Essential Amino Acids**: Essential amino acids are those that cannot be synthesized by the human body and must be obtained through diet. This is crucial because our body relies on these amino acids for various functions, including protein synthesis.

2. **Identifying the Options**: The question provides several options to choose from. In this case, the options are serine, aspartic acid, glycine, and phenylalanine.

3. **Evaluating Each Option**:
- **Serine**: This amino acid is produced by the body, so it is not an essential amino acid.
- **Aspartic Acid**: This is also produced by the body, and while it can be consumed through diet (like citrus fruits), it is not classified as essential.
- **Glycine**: Similar to serine and aspartic acid, glycine is produced by the body and is not essential.
- **Phenylalanine**: This amino acid is not produced by the body and must be obtained from food sources. It is classified as an essential amino acid.

4. **Conclusion**: Among the options provided, phenylalanine is the only essential amino acid because it cannot be synthesized by the body and must be consumed through diet.

**Final Answer**: Phenylalanine is an essential amino acid.

---