Which of the following is not a salient feature of B-DNA ?

Options

A. One full turn of helical strand involves 10 base pairs
B. Pitch of helix would be 34 Å
C. Diameter of double helix would be 20 Å
D. DNA with left handed coiling

Answer

To determine which of the following is not a salient feature of B-DNA, we need to analyze the characteristics of B-DNA as described by Watson and Crick in their model.

### Step-by-Step Solution:

1. **Understanding B-DNA Structure**:
- B-DNA is the most common form of DNA in cells. It is a right-handed double helix.

2. **Key Features of B-DNA**:
- **Helical Structure**: B-DNA has a right-handed helical structure.
- **Base Pairs**: Each complete turn of the helix contains 10 base pairs.
- **Pitch of Helix**: The pitch of the helix (the distance for one complete turn) is approximately 34 angstroms (3.4 nm).
- **Diameter**: The diameter of the B-DNA double helix is about 20 angstroms (2 nm).
- **Distance Between Base Pairs**: The distance between adjacent base pairs is approximately 0.34 nm (3.4 angstroms).
- **Angular Distance**: Each base pair contributes an angular distance of about 36 degrees to the helical structure.

3. **Identifying the Incorrect Feature**:
- The question asks for a feature that is not characteristic of B-DNA. If an option states that B-DNA has a left-handed coil, this would be incorrect, as B-DNA is a right-handed helix.

4. **Conclusion**:
- The salient feature that is not present in B-DNA is the left-handed coil. Therefore, if one of the options indicates that B-DNA has a left-handed coil, that would be the correct answer to the question.

### Final Answer:
The feature that is not a salient feature of B-DNA is that it has a left-handed coil.

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