If a ligand is lipid-soluble, where is the receptor most likely located?

If a ligand is lipid-soluble, where is the receptor most likely located?

• A. On the cell surface.
• B. In the mitochondria.
• C. Intracellular or nuclear locations.
• D. In the endoplasmic reticulum.

Answer: (C)

Lipid-soluble ligands can cross the cell membrane, so their receptors are typically inside the cell—either in the cytosol or in the nucleus. Once the ligand binds, the receptor often acts as or modulates a transcription factor, changing gene expression. This leads to slower onset but longer-lasting effects because the cell must synthesize new proteins to mediate the response. Classic examples include steroid hormones and thyroid hormone. In contrast, ligands that can’t cross the membrane easily bind to receptors on the cell surface and trigger rapid signaling cascades through second messengers. Receptors in mitochondria or the endoplasmic reticulum aren’t the primary sites for the action of lipid-soluble ligands. Therefore, the receptor is most likely intracellular or nuclear.

Lipid-soluble ligands can cross the cell membrane, so their receptors are typically inside the cell—either in the cytosol or in the nucleus. Once the ligand binds, the receptor often acts as or modulates a transcription factor, changing gene expression. This leads to slower onset but longer-lasting effects because the cell must synthesize new proteins to mediate the response. Classic examples include steroid hormones and thyroid hormone.

In contrast, ligands that can’t cross the membrane easily bind to receptors on the cell surface and trigger rapid signaling cascades through second messengers. Receptors in mitochondria or the endoplasmic reticulum aren’t the primary sites for the action of lipid-soluble ligands. Therefore, the receptor is most likely intracellular or nuclear.