In a segment of DNA molecule there occurs 200 molecules of adenine nitrogen bases and 200 molecules of cytosine nitrogen bases. What will be the total number of purine nitrogen bases in this segment ?

Options

A. 800
B. 400
C. 100
D. 200

Answer

To solve the problem, we need to identify the types of nitrogen bases present in the DNA segment and then calculate the total number of purine bases.

### Step-by-Step Solution:

1. **Identify the Nitrogen Bases**:
In DNA, there are four types of nitrogen bases: adenine (A), thymine (T), cytosine (C), and guanine (G). Among these, adenine and guanine are classified as purines, while thymine and cytosine are classified as pyrimidines.

2. **Count the Purine Bases**:
From the information given in the question, we know that there are:
- 200 molecules of adenine (A)
- 200 molecules of cytosine (C)

Since cytosine is a pyrimidine, we do not count it as a purine. Therefore, the only purine base present in the segment is adenine.

3. **Calculate the Total Number of Purines**:
The total number of purine nitrogen bases in the segment is equal to the number of adenine molecules, as there are no guanine molecules mentioned in the question.

Total purine bases = Number of adenine (A) + Number of guanine (G)
Since guanine is not mentioned, we can assume it to be 0.

Total purine bases = 200 (A) + 0 (G) = 200

4. **Final Answer**:
The total number of purine nitrogen bases in this segment of DNA is **200**.