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

Options

A. four
B. five
C. ten
D. Uncertain

Answer

To determine the average number of purine nitrogen bases present in a single coil of DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of DNA**:
- DNA is a long polymer made up of repeating units called nucleotides. Each nucleotide consists of a nitrogenous base, a deoxyribose sugar, and a phosphate group.

2. **Identify the Types of Nitrogenous Bases**:
- The nitrogenous bases in DNA are categorized into two types: purines and pyrimidines. The purines are adenine (A) and guanine (G), while the pyrimidines are cytosine (C) and thymine (T).

3. **Recognize the Pairing of Bases**:
- 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 Coil**:
- A single coil of DNA contains approximately 10.5 base pairs. This is a crucial piece of information because it helps us understand how many bases are present in a single coil.

5. **Calculate the Average Number of Purine Bases**:
- Since there are 10.5 base pairs in a single coil of DNA, and each pair consists of one purine and one pyrimidine, we can conclude that there will be approximately 10 purine bases (since we round down from 10.5).

6. **Final Answer**:
- Therefore, on average, there are **10 purine nitrogen bases** present in a single coil of DNA.

### Summary:
On an average, the number of purine nitrogen bases present in a single coil of DNA is **10**.