The following group/linkage is absent in Adenine but present in Guanine

Options

A. `-C-=N`
B. `-NH_(2)`
C. `gt C=O`
D. `-C_NH_(2)`

Answer

To determine the group or linkage that is absent in adenine but present in guanine, we need to analyze the structures of both molecules.

### Step-by-Step Solution:

1. **Draw the Structure of Adenine:**
- Adenine is a purine base with the following structure:
- It contains five nitrogen atoms and five carbon atoms.
- The structure can be represented as:
```
N
\
C
/ \
N C
| |
C---N
|
N
```
- In this structure, adenine has an amino group (-NH2) attached to one of the carbon atoms.

2. **Draw the Structure of Guanine:**
- Guanine is also a purine base, but it has a different structure:
- It contains the same number of nitrogen and carbon atoms as adenine but has an additional carbonyl group (C=O).
- The structure can be represented as:
```
O
||
C
/ \
N C
| |
C---N
|
N
```
- In guanine, there is an amino group (-NH2) and a carbonyl group (C=O) present.

3. **Identify the Differences:**
- By comparing the two structures, we can observe that:
- Both adenine and guanine have an amino group (-NH2).
- Guanine has an additional carbonyl group (C=O) that is not present in adenine.

4. **Conclusion:**
- The group that is absent in adenine but present in guanine is the carbonyl group (C=O).

### Final Answer:
The group/linkage that is absent in adenine but present in guanine is the **carbonyl group (C=O)**.