Question

Which of the following signal molecules does not interact with cell surface receptors?

• A. Insulin
• B. Gastrin
• C. Glucagon
• D. Testosterone

Hint:

Steroid hormones, like testosterone, enter cells and act on intracellular receptors, while peptide hormones like insulin and glucagon interact with receptors on the cell surface.

Answer 1

The Correct Option is D

Testosterone is a steroid hormone that is lipophilic (fat-soluble). Because of its lipophilic nature, testosterone can easily pass through the cell membrane and bind to intracellular receptors within the cytoplasm or nucleus. These intracellular receptors then initiate gene transcription and affect cellular processes.

(1) Testosterone:
- Unlike water-soluble signal molecules such as insulin, gastrin, and glucagon, which bind to cell surface receptors, testosterone binds to intracellular receptors to exert its effects on gene expression.

(2) Why Other Options Are Incorrect:
- Insulin (Option 1) is a peptide hormone that binds to receptors on the cell surface and triggers a signaling cascade inside the cell.
- Gastrin (Option 2) is a peptide hormone that interacts with receptors on the surface of target cells in the stomach to stimulate gastric acid secretion.
- Glucagon (Option 3) is another peptide hormone that binds to cell surface receptors, particularly in the liver, to regulate blood glucose levels.

Conclusion: Testosterone does not interact with cell surface receptors but instead interacts with intracellular receptors, making it the correct answer.