Which of the following correctly describes intracellular receptor characteristics?

• A. They are located in the cytosol only and do not translocate to the nucleus.
• B. They are membrane-bound receptors that do not cross the membrane.
• C. They bind ligands that are water-soluble.
• D. Some intracellular receptors are found in the nucleus or translocated to the nucleus after ligand binding; their ligands are lipid soluble to cross the plasma membrane (steroid hormones).

Answer: (D)

Intracellular receptors reside inside the cell, either in the cytosol or already in the nucleus, and they require lipid-soluble ligands that can cross the plasma membrane. When such a ligand binds, the receptor often moves into the nucleus (if it started in the cytosol) and acts as a transcription factor to regulate gene expression. Some intracellular receptors are already in the nucleus and respond without moving, but in all cases the signal ultimately changes which genes are turned on or off. This class includes steroid hormones like cortisol, aldosterone, estrogens, and androgens, whose lipid-soluble nature lets them access these receptors. Because the effect is to alter gene transcription, the response is typically slower than signaling via membrane-bound receptors. The other descriptions aren’t correct because water-soluble ligands can’t cross the membrane to reach intracellular receptors, and membrane-bound receptors function at the cell surface rather than inside the cell.