In .Z. DNA, pitch of each turn of helix is

Options

A. 34 Å
B. 340 nm
C. 250 nm
D. 45 Å

Answer

To solve the question regarding the pitch of each turn of the helix in Z-DNA, we will follow these steps:

### Step-by-Step Solution:

1. **Understand Z-DNA Structure**:
- Z-DNA is one of the three forms of DNA, alongside A-DNA and B-DNA. It has a unique left-handed helical structure, which distinguishes it from the right-handed helices of A and B-DNA.

2. **Identify the Pitch of Helix**:
- The pitch of a DNA helix refers to the distance between one complete turn of the helix. For Z-DNA, this measurement is critical to understanding its structural properties.

3. **Refer to Known Values**:
- The pitch of Z-DNA is a well-documented value in molecular biology. It is known that the pitch of Z-DNA is approximately 45 Ångstroms (Å).

4. **Select the Correct Option**:
- Given the options provided in the question (34 Å, 340 nanometers, 250 nanometers, and 45 Å), we can conclude that the correct answer is 45 Ångstroms.

5. **Final Answer**:
- Therefore, the pitch of each turn of the helix in Z-DNA is **45 Ångstroms**.