Which statement best describes an agonist?

Which statement best describes an agonist?

• A. Binds to receptor but does not activate
• B. Activates a receptor by binding to that receptor
• C. Does not interact with receptors
• D. Binds to receptor and blocks its action

Answer: (B)

An agonist produces a response by turning on the receptor it binds to. When a molecule fits a receptor and changes its shape to initiate signaling, it activates the receptor and generates downstream effects, such as opening ion channels or triggering second-messenger pathways. This is what gives a physiological effect, like morphine activating mu receptors to produce analgesia. In contrast, binding without activation sits in the receptor and blocks signaling (antagonist), binding and blocking its action is likewise antagonistic, and a molecule that doesn’t interact with receptors has no effect. Therefore, the best description is that an agonist activates a receptor by binding to it.

An agonist produces a response by turning on the receptor it binds to. When a molecule fits a receptor and changes its shape to initiate signaling, it activates the receptor and generates downstream effects, such as opening ion channels or triggering second-messenger pathways. This is what gives a physiological effect, like morphine activating mu receptors to produce analgesia. In contrast, binding without activation sits in the receptor and blocks signaling (antagonist), binding and blocking its action is likewise antagonistic, and a molecule that doesn’t interact with receptors has no effect. Therefore, the best description is that an agonist activates a receptor by binding to it.