X' is physiologically and biologically active from of DNA . The pitch of its helix is `34Å` with a distance between two adjacent base pair of about `3.4Å` It shows right-handed coiling. Identify 'X'

Options

A. B - DNA
B. A - DNA
C. Z - DNA
D. C - DNA

Answer

To solve the question regarding the identification of 'X', which is described as a physiologically and biologically active form of DNA with specific characteristics, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Characteristics of 'X':**
- The question states that 'X' has a pitch of its helix equal to 34 Å (Angstroms).
- The distance between two adjacent base pairs is given as 3.4 Å.
- It is specified that 'X' shows right-handed coiling.

2. **Calculating the Number of Base Pairs:**
- The pitch of the helix (34 Å) is the distance for one complete turn of the helix.
- The distance between adjacent base pairs is 3.4 Å.
- To find the number of base pairs in one complete turn of the helix, we can use the formula:
\[ \text{Number of base pairs} = \frac{\text{Pitch}}{\text{Distance between base pairs}} = \frac{34 \, \text{Å}}{3.4 \, \text{Å}} = 10 \]
- This calculation shows that there are 10 base pairs per turn in the helix.

3. **Identifying the Type of DNA:**
- The characteristics of DNA types are as follows:
- **A-DNA:** Has about 11 base pairs per turn and is not typically right-handed.
- **B-DNA:** Has about 10 base pairs per turn, is right-handed, and is the most common form of DNA in physiological conditions.
- **Z-DNA:** Has about 12 base pairs per turn and has a zigzag structure, also right-handed but less common.
- **cDNA:** Generally has fewer base pairs and is not a standard form of DNA.
- Given that 'X' has 10 base pairs per turn and is right-handed, it matches the characteristics of B-DNA.

4. **Conclusion:**
- Based on the calculations and the characteristics of the different forms of DNA, we can conclude that 'X' is **B-DNA**.

### Final Answer:
**X is B-DNA.**