The base pairs per turn of the helix in A-DNA is

Options

A. 10
B. 12
C. 11
D. 8

Answer

To determine the number of base pairs per turn of the helix in A-DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of A-DNA**:
- A-DNA is one of the forms of DNA, which is more compact than B-DNA. It is typically found in dehydrated conditions and is characterized by its right-handed helical structure.

2. **Compare A-DNA with B-DNA**:
- B-DNA is the most common form of DNA found in living organisms, including humans. It has a specific structure that allows for 10 base pairs per turn of the helix.
- A-DNA, on the other hand, is shorter and more compact than B-DNA, which affects the number of base pairs per turn.

3. **Determine the Base Pairs per Turn**:
- In A-DNA, the base pairs are more tightly packed due to the compact nature of the helix. This results in a higher number of base pairs per turn compared to B-DNA.
- Specifically, A-DNA has approximately **11 base pairs per turn**.

4. **Conclusion**:
- Based on the structural characteristics and comparison with B-DNA, we conclude that the number of base pairs per turn in A-DNA is **11**.

### Final Answer:
The base pairs per turn of the helix in A-DNA is **11**.