Examples of actions not mediated by receptors include

Examples of actions not mediated by receptors include

• A. Neutralization of gastric acid by a base
• B. Activation of a receptor by a ligand
• C. Inhibition of receptor signaling by a competitive antagonist
• D. Internal signaling cascades triggered by G-proteins

Answer: (A)

Chemical actions that do not involve receptor proteins are simple chemical processes that occur in solution rather than through receptor binding and signaling. Neutralization of gastric acid by a base is such a process: the base directly reacts with the acid in the stomach to form salt and water, without any receptor binding, no receptor activation, and no intracellular signaling. In contrast, the other scenarios rely on receptors. Activating a receptor by a ligand requires the ligand to bind to the receptor and induce a conformational change. Blocking receptor signaling with a competitive antagonist directly interferes with that binding or activation. Internal signaling cascades initiated by G-proteins start only after receptor activation and involve intracellular transduction steps.

Chemical actions that do not involve receptor proteins are simple chemical processes that occur in solution rather than through receptor binding and signaling. Neutralization of gastric acid by a base is such a process: the base directly reacts with the acid in the stomach to form salt and water, without any receptor binding, no receptor activation, and no intracellular signaling.

In contrast, the other scenarios rely on receptors. Activating a receptor by a ligand requires the ligand to bind to the receptor and induce a conformational change. Blocking receptor signaling with a competitive antagonist directly interferes with that binding or activation. Internal signaling cascades initiated by G-proteins start only after receptor activation and involve intracellular transduction steps.