Lysine and tryptophan are

Options

A. proteins
B. non-essential amino acids
C. essential amino acids
D. aromatic amino acids.

Answer

To solve the question "Lysine and tryptophan are," we need to identify the correct classification of these two amino acids from the given options: proteins, non-essential amino acids, essential amino acids, and aromatic amino acids.

### Step-by-Step Solution:

1. **Understanding Amino Acids**:
- Amino acids are the building blocks of proteins. They play a crucial role in various biological processes.

2. **Categories of Amino Acids**:
- Amino acids can be classified into two main categories:
- **Essential Amino Acids**: These are amino acids that cannot be synthesized by the body and must be obtained from the diet.
- **Non-Essential Amino Acids**: These can be synthesized by the body and do not need to be obtained from dietary sources.

3. **Identifying Lysine and Tryptophan**:
- **Lysine**: This is an essential amino acid. It is crucial for protein synthesis and must be obtained through food.
- **Tryptophan**: This is also an essential amino acid. It is important for the production of serotonin and must also be obtained from the diet.

4. **Evaluating the Options**:
- **Proteins**: This option is incorrect because lysine and tryptophan are not proteins; they are amino acids.
- **Non-Essential Amino Acids**: This option is incorrect because both lysine and tryptophan are essential amino acids, not non-essential.
- **Essential Amino Acids**: This option is correct as both lysine and tryptophan fall into this category.
- **Aromatic Amino Acids**: This option is incorrect because while tryptophan is an aromatic amino acid, lysine is not.

5. **Conclusion**:
- The correct answer is **essential amino acids**.

### Final Answer:
Lysine and tryptophan are **essential amino acids**.