What describes an agonist?

What describes an agonist?

• A. A molecule that binds to a receptor, producing a physiological or pharmacological response; mimics the effects of the endogenous compound
• B. A molecule that binds to a receptor and decreases the effect of an agonist
• C. A molecule that binds to a receptor but does not produce any response
• D. A molecule that inhibits receptor synthesis

Answer: (A)

An agonist is a molecule that binds to a receptor and activates it, triggering a cellular response. It often mimics the endogenous signaling molecule, so the effect resembles the body’s natural signal. That’s why choosing a description that emphasizes binding plus activation and a resulting response is the best fit. The other ideas describe different roles: a molecule that binds and reduces the effect of an agonist acts as an antagonist, blocking receptor activation. A molecule that binds but produces no response is a ligand with no efficacy (a non-efficacious or neutral ligand, often acting as an antagonist). A molecule that inhibits receptor synthesis changes how many receptors are available, not the immediate activation of a receptor, so it isn’t an agonist.

An agonist is a molecule that binds to a receptor and activates it, triggering a cellular response. It often mimics the endogenous signaling molecule, so the effect resembles the body’s natural signal. That’s why choosing a description that emphasizes binding plus activation and a resulting response is the best fit.

The other ideas describe different roles: a molecule that binds and reduces the effect of an agonist acts as an antagonist, blocking receptor activation. A molecule that binds but produces no response is a ligand with no efficacy (a non-efficacious or neutral ligand, often acting as an antagonist). A molecule that inhibits receptor synthesis changes how many receptors are available, not the immediate activation of a receptor, so it isn’t an agonist.