An antagonist is characterized by which statement?

An antagonist is characterized by which statement?

• A. Binds to receptor without activating
• B. Activates receptor to produce a response
• C. Increases receptor sensitivity
• D. Blocks receptor by downregulating receptor numbers

Answer: (A)

An antagonist binds to a receptor but does not activate it, so it blocks the receptor from signaling in response to an agonist. This lack of intrinsic activity means the molecule itself doesn’t produce a cellular response, it simply prevents activation by other ligands. In contrast, an agonist binds and activates the receptor to produce a response. The idea of increasing receptor sensitivity describes something that enhances response, not block it. Downregulating receptor numbers describes a change in receptor density over time, which is a separate adaptive process and not the defining action of an antagonist. So the defining feature is binding without activation, which prevents receptor signaling.

An antagonist binds to a receptor but does not activate it, so it blocks the receptor from signaling in response to an agonist. This lack of intrinsic activity means the molecule itself doesn’t produce a cellular response, it simply prevents activation by other ligands. In contrast, an agonist binds and activates the receptor to produce a response. The idea of increasing receptor sensitivity describes something that enhances response, not block it. Downregulating receptor numbers describes a change in receptor density over time, which is a separate adaptive process and not the defining action of an antagonist. So the defining feature is binding without activation, which prevents receptor signaling.