In purines, N is at position _____in its two rinigs.

Options

A. 1,3,7,9
B. 1,5
C. 7,9
D. 1&9

Answer

To answer the question regarding the position of nitrogen (N) in purines, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Purines**:
- Purines are a type of nitrogenous base that consist of two fused rings. The two main purines found in nucleic acids are adenine and guanine.

2. **Identify the Numbering of Atoms**:
- The purine structure has a specific numbering system for its atoms. The numbering starts from one of the nitrogen atoms and continues around the rings.

3. **Numbering of the Rings**:
- The first ring is numbered in an anti-clockwise direction, and the second ring is numbered in a clockwise direction. The positions are as follows:
- For the first ring: 1, 2, 3, 4, 5, 6
- For the second ring: 7, 8, 9

4. **Locate the Nitrogen Atoms**:
- In the purine structure:
- Nitrogen is found at position 1 (N1) in the first ring.
- Nitrogen is also found at position 7 (N7) in the second ring.
- Additionally, in guanine, there is another nitrogen at position 9 (N9) in the second ring.

5. **Conclusion**:
- Therefore, in purines, nitrogen (N) is located at positions 1 and 7 (and also at 9 in guanine).

### Final Answer:
In purines, N is at positions **1 and 7** (and also at 9 in guanine).

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