What is the role of second messenger in the mechanism of protein hormone action?

Explanation

### Step-by-Step Solution:

1. **Understanding Protein Hormones**:
- Protein hormones are large molecules that cannot easily cross the cell membrane. They bind to specific receptors on the surface of target cells.

2. **Role of Receptors**:
- When a protein hormone binds to its receptor on the cell membrane, it triggers a series of events inside the cell. This binding does not directly cause a response but initiates a signaling cascade.

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