Which of the following is secondary messenger :

Options

A. ATP
B. Cyclic AMP
C. GTP
D. ATP and AMP

Answer

To determine which of the following options is a secondary messenger, we can analyze each option provided:

1. **ATP (Adenosine Triphosphate)**: This is primarily known as the energy currency of the cell. It is not classified as a secondary messenger.

2. **Cyclic AMP (cAMP)**: This is a well-known secondary messenger involved in various signaling pathways within cells. It is generated from ATP by the action of the enzyme adenylate cyclase when a hormone binds to its receptor.

3. **GTP (Guanosine Triphosphate)**: Similar to ATP, GTP is also primarily known as an energy molecule and is involved in protein synthesis and signal transduction but is not classified as a secondary messenger.

4. **AMP (Adenosine Monophosphate)**: While AMP can play roles in cellular signaling, it is not typically classified as a secondary messenger in the same way that cAMP is.

Based on this analysis, the only option that fits the definition of a secondary messenger is **Cyclic AMP (cAMP)**.

### Final Answer:
**Cyclic AMP (cAMP)** is the secondary messenger.