What describes the receptor's role in pharmacodynamics?

• A. Binds to ligands but does not initiate signaling
• B. Initiates signaling only after gene transcription
• C. Binds ligands with specificity to initiate downstream events
• D. Degrades ligands immediately after binding

Answer: (C)

Receptors translate drug binding into a cellular response by binding ligands with specificity and initiating downstream signaling. The defining role is not just to hold the drug, but to undergo changes that activate signaling pathways—whether rapid second-messenger cascades, ion channel modulation, or longer-term effects like altered gene transcription. That makes the description of binding ligands with specificity to initiate downstream events the best answer. It wouldn’t be accurate to say receptors merely bind without signaling, since the primary function is to generate a cellular response from that binding. And degradation of ligands is not a typical receptor function; that task lies with other proteins such as enzymes or transporters.