Which of the following has an aromatic ring ?

Options

A. Alanine
B. Lycine
C. Tyrosine
D. Glycine

Explanation

To determine which of the given amino acids has an aromatic ring, we need to analyze the structures of each amino acid provided in the question: alanine, lysine, tyrosine, and glycine.

### Step-by-Step Solution:

1. **Identify the Structures of the Amino Acids:**
- **Alanine (Ala)**: The structure of alanine consists of a central carbon atom bonded to an amino group (NH2), a carboxyl group (COOH), a hydrogen atom (H), and a methyl group (CH3). It does not contain an aromatic ring.
- **Lysine (Lys)**: The structure of lysine includes a central carbon atom bonded to an amino group (NH2), a carboxyl group (COOH), a hydrogen atom (H), and a long aliphatic chain with two additional amino groups. It also does not contain an aromatic ring.
- **Tyrosine (Tyr)**: The structure of tyrosine includes a central carbon atom bonded to an amino group (NH2), a carboxyl group (COOH), a hydrogen atom (H), and a phenolic side chain (which includes a benzene ring). This side chain is what gives tyrosine its aromatic character.
- **Glycine (Gly)**: The structure of glycine consists of a central carbon atom bonded to an amino group (NH2), a carboxyl group (COOH), and a hydrogen atom (H). Glycine does not have an aromatic ring.

2. **Analyze for Aromaticity:**
- An aromatic ring is characterized by a cyclic structure with alternating double bonds and is typically planar, allowing for delocalization of pi electrons. Among the amino acids analyzed, only tyrosine has a phenolic side chain that contains a benzene ring, which is aromatic.

3. **Conclusion:**
- Among alanine, lysine, tyrosine, and glycine, **tyrosine** is the only amino acid that contains an aromatic ring.

### Final Answer:
**Tyrosine (Tyr)** has an aromatic ring.