To determine which of the given options is an amino acid, we need to understand the basic structure of an amino acid. Here’s a step-by-step breakdown of the solution:
### Step 1: Understand the Structure of Amino Acids
Amino acids have a general structure that includes:
- An amino group (-NH2)
- A carboxyl group (-COOH)
- A hydrogen atom (H)
- An alpha carbon (Cα) that is bonded to a side chain (R group)
### Step 2: Analyze the Given Options
We need to examine each option provided in the question to see if it fits the structure of an amino acid.
1. **Option 1**: Check for the presence of an amino group, carboxyl group, alpha carbon, and side chain.
- **Evaluation**: This option does not have an alpha carbon, making it incorrect.
2. **Option 2**: Again, check for the amino group, carboxyl group, alpha carbon, and side chain.
- **Evaluation**: This option also lacks the correct structure, particularly the placement of the amino group, making it incorrect.
3. **Option 3**: Analyze this option for the necessary components.
- **Evaluation**: Similar to the previous options, this one does not have the alpha carbon, making it incorrect.
4. **Option 4**: Check if this option has all the necessary components.
- **Evaluation**: This option has the amino group, carboxyl group, alpha carbon, and a side chain (R group). This structure matches that of proline, which is a neutral amino acid.
### Step 3: Identify the Correct Answer
Based on the analysis, the correct answer is the fourth option, which is proline, as it contains all the necessary components of an amino acid.
### Final Answer:
The correct answer is **proline**.
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