On an average, hwo many purine `N_(2)` bases are present in single coil of DNA

Options

A. Four
B. Five
C. Ten
D. Uncertain

Answer

To solve the question of how many purine nitrogenous bases are present in a single coil of DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of DNA**:
- DNA is composed of nucleotides, which consist of a nitrogenous base, a deoxyribose sugar, and a phosphate group.
- The nitrogenous bases are categorized into two types: purines and pyrimidines.

2. **Identify the Types of Bases**:
- Purines include adenine (A) and guanine (G).
- Pyrimidines include cytosine (C) and thymine (T).

3. **Base Pairing in DNA**:
- In the double helix structure of DNA, purines pair with pyrimidines. Specifically, adenine pairs with thymine, and guanine pairs with cytosine.

4. **Determine the Number of Base Pairs in a Single Coil**:
- It is known that there are approximately 10.5 base pairs in one complete turn (or coil) of the DNA helix.

5. **Calculate the Number of Purines**:
- Since each base pair consists of one purine and one pyrimidine, in 10.5 base pairs, there will be approximately 10.5 purines.
- However, since we are looking for an average whole number, we can round this down to 10 purines.

6. **Conclusion**:
- Therefore, on average, there are about 10 purine nitrogenous bases present in a single coil of DNA.

### Final Answer:
The average number of purine nitrogenous bases in a single coil of DNA is **10**.

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