What is the primary difference between agonists and antagonists in GPCR signaling?

• A. Agonists mimic the effect of natural ligands, while antagonists block the effect.
• B. Agonists block the effect of natural ligands, while antagonists mimic the effect.
• C. Both agonists and antagonists mimic the effect of natural ligands.
• D. Both agonists and antagonists block the effect of natural ligands.

Answer: (A)