Which are examples of intracellular receptors?

• A. Thyroid hormone receptors
• B. Surface receptor tyrosine kinases
• C. G protein-coupled receptors
• D. Ion channel receptors

Answer: (A)

Intracellular receptors are able to respond to ligands that cross the cell membrane and then directly regulate gene expression, usually by acting as transcription factors in the nucleus. Thyroid hormone receptors fit this idea perfectly—they reside inside the cell (in the nucleus) and bind thyroid hormones, which then modulate transcription of target genes. In contrast, surface receptor tyrosine kinases, G protein-coupled receptors, and ion channel receptors are all embedded in the cell membrane and signal from the surface through kinases, G proteins, or ion flux rather than by directly controlling gene transcription. So the thyroid hormone receptor is the example of an intracellular receptor.