The site of action of insulin is

Options

A. mitochondria
B. nucleus
C. plasma membrane
D. DNA

Answer

**Step-by-Step Solution:**

1. **Understanding Insulin's Role**: Insulin is a hormone produced by the pancreas that plays a crucial role in regulating blood glucose levels. It facilitates the uptake of glucose by cells, particularly in the liver and muscles.

2. **Identifying the Target Cells**: The primary target cells for insulin action are liver cells (hepatocytes) and muscle cells (myocytes). These cells have specific receptors for insulin on their surfaces.

3. **Insulin Receptors**: Insulin binds to insulin receptors located on the plasma membrane of these target cells. The binding of insulin to its receptor triggers a series of cellular responses.

4. **Glucose Transport Mechanism**: When insulin binds to its receptor, it activates a glucose transporter (GLUT) within the cell. This transporter moves to the plasma membrane and forms a channel through which glucose can enter the cell.

5. **Conclusion**: The site of action of insulin is the plasma membrane of the target cells (liver and muscle cells) where it binds to insulin receptors, facilitating glucose uptake.

**Final Answer**: The site of action of insulin is the plasma membrane of target cells.

---