Which statement correctly describes intracellular receptors?

Which statement correctly describes intracellular receptors?

• A. Located on the cell surface and respond to hydrophilic ligands
• B. Located in the mitochondria
• C. Located inside the cell; ligand must be lipid soluble to cross the cell membrane
• D. They respond to all ligands equally

Answer: (C)

Intracellular receptors are located inside the cell, typically in the cytoplasm or nucleus, and they are activated by ligands that can cross the cell membrane. For this to happen, the ligand must be lipid-soluble (or very small) so it can diffuse through the lipid bilayer. Once the ligand binds, the receptor often acts as a transcription factor, changing gene expression to elicit a response. This is the reason lipid-soluble hormones like steroids and thyroid hormone fit this mechanism. Signals that stay outside the cell and are hydrophilic bind to receptors on the cell surface because they cannot cross the membrane. While there are receptors associated with mitochondria, the defining feature of intracellular receptors is their intracellular localization, not a mitochondrial site. Intracellular receptors are also not equipped to respond to all ligands equally; specificity relies on compatibility between the ligand and the receptor’s binding site.

Intracellular receptors are located inside the cell, typically in the cytoplasm or nucleus, and they are activated by ligands that can cross the cell membrane. For this to happen, the ligand must be lipid-soluble (or very small) so it can diffuse through the lipid bilayer. Once the ligand binds, the receptor often acts as a transcription factor, changing gene expression to elicit a response. This is the reason lipid-soluble hormones like steroids and thyroid hormone fit this mechanism.

Signals that stay outside the cell and are hydrophilic bind to receptors on the cell surface because they cannot cross the membrane. While there are receptors associated with mitochondria, the defining feature of intracellular receptors is their intracellular localization, not a mitochondrial site. Intracellular receptors are also not equipped to respond to all ligands equally; specificity relies on compatibility between the ligand and the receptor’s binding site.