Pitch of `alpha`-helix of a polypeptide is

Options

A. 7.0 Å
B. 5.4 Å
C. 3.4 Å
D. 34 Å

Answer

To determine the pitch of an alpha-helix in a polypeptide, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Alpha-Helix**:
- The alpha-helix is a common secondary structure in proteins characterized by a right-handed spiral configuration.

2. **Identify Key Parameters**:
- The alpha-helix has specific parameters that define its structure:
- It typically has **3.6 amino acids per turn**.
- Each amino acid contributes to the rise of the helix.

3. **Calculate the Rise per Residue**:
- The rise per residue in an alpha-helix is approximately **1.5 angstroms**.

4. **Calculate the Total Rise for One Turn**:
- Since there are 3.6 residues per turn, the total rise (or pitch) for one complete turn of the helix can be calculated as:
\[ \text{Pitch} = \text{Number of residues per turn} \times \text{Rise per residue} \]
\[ \text{Pitch} = 3.6 \times 1.5 \, \text{angstroms} = 5.4 \, \text{angstroms} \]

5. **Conclusion**:
- Therefore, the pitch of the alpha-helix of a polypeptide is **5.4 angstroms**.

### Final Answer:
The pitch of an alpha-helix of a polypeptide is **5.4 angstroms**.

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