What is the mechanism of action for steroid hormones?

• A. They bind to cell surface receptors.
• B. They pass through cell membranes and bind to intracellular receptors.
• C. They stimulate the release of other hormones.
• D. They directly alter DNA transcription.

Answer: (B)

Steroid hormones have a unique mechanism of action characterized by their ability to pass through the lipid bilayer of cell membranes due to their hydrophobic nature. Once inside the cell, they typically bind to specific intracellular receptors located in the cytoplasm or the nucleus.

This binding initiates a cascade of events that often includes the receptor-hormone complex moving into the nucleus, where it can interact with DNA. This interaction can lead to the regulation of gene expression, influencing the transcription of specific genes that control various physiological processes.

The capacity to directly affect gene transcription is a hallmark of steroid hormones, making them fundamentally different from hormones that rely on cell surface receptors, which generally initiate a process involving signal transduction pathways rather than directly influencing DNA.

In summary, the mechanism of action for steroid hormones involves their passage through cell membranes, formation of a receptor complex, and eventual alteration of transcription in the nucleus, which is why the correct answer focuses on their binding to intracellular receptors.