Which of the following structures represents the peptide chain?

Options

A. `-underset|oversetoversetH|N-undersetOunderset(||)C-underset|overset|C-underset|overset|C-underset|overset|C-oversetHoverset|N-underset|overset|C-underset|overset|C-underset|overset|C-`
B. `-oversetHoverset|N-underset|overset|C-undersetunderset(O)(||)C-oversetoverset(H)|N-underset|overset|C-oversetoversetO(||)C-`
C. `-oversetoverset(H)|N-underset|overset|C-underset|overset|C-oversetoversetO(||)C-undersetundersetH|N-underset|overset|C-underset|overset|C-oversetoversetH|N-undersetundersetO(||)C-underset|overset|C-underset|overset|C`
D. `-oversetoversetH|N-undersetunderset(O)(||)C-undersetunderset(H)(|)N-underset|overset|C-NH-oversetoversetO(||)C-NH-`

Answer

To determine which structure represents a peptide chain, we need to understand the characteristics of a peptide bond and the structure of amino acids.

### Step-by-Step Solution:

1. **Understand the Structure of Amino Acids**:
- Amino acids are the building blocks of proteins. Each amino acid has a basic amino group (–NH2), an acidic carboxyl group (–COOH), and a variable side chain (R group).
- The general structure of an amino acid can be represented as:
```
H2N–C(R)–COOH
```

2. **Define a Peptide Bond**:
- A peptide bond is formed when the carboxyl group of one amino acid reacts with the amino group of another, releasing a molecule of water (H2O).
- The reaction can be summarized as follows:
```
Amino Acid 1 + Amino Acid 2 → Peptide + H2O
```

3. **Identify the Peptide Chain Structure**:
- A peptide chain consists of multiple amino acids linked by peptide bonds. It will have:
- An N-terminal (the end with the free amino group).
- A C-terminal (the end with the free carboxyl group).
- At least one peptide bond between two amino acids.

4. **Analyze the Given Options**:
- Check each option for the presence of:
- An N-terminal.
- A C-terminal.
- At least one peptide bond.
- Evaluate each structure one by one.

5. **Select the Correct Option**:
- After analyzing all options:
- **Option A**: Lacks a C-terminal and does not have a peptide bond.
- **Option B**: Contains both N-terminal and C-terminal, along with a peptide bond. This is the correct option.
- **Option C**: Lacks a C-terminal.
- **Option D**: Lacks a C-terminal.

### Conclusion:
The correct answer is **Option B**, as it contains both the N-terminal and C-terminal along with a peptide bond.

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