Which term best describes a ligand produced outside the body but that binds to a receptor?

Which term best describes a ligand produced outside the body but that binds to a receptor?

• A. Endogenous ligand
• B. Allosteric ligand
• C. Inverse agonist
• D. Exogenous ligand

Answer: (D)

Origin of the ligand is being tested: a molecule that binds a receptor can come from inside the body or from outside. When a molecule originates outside the body and still binds the receptor, it’s called an exogenous ligand. This distinguishes it from an endogenous ligand, which is produced within the body, such as natural hormones or neurotransmitters. The other terms refer to different ideas: an allosteric ligand binds at a site other than the primary active site and modulates activity, not origin; an inverse agonist describes the effect on receptor activity rather than where the ligand comes from. So the correct term specifically captures that external, non-body-produced source.

Origin of the ligand is being tested: a molecule that binds a receptor can come from inside the body or from outside. When a molecule originates outside the body and still binds the receptor, it’s called an exogenous ligand. This distinguishes it from an endogenous ligand, which is produced within the body, such as natural hormones or neurotransmitters. The other terms refer to different ideas: an allosteric ligand binds at a site other than the primary active site and modulates activity, not origin; an inverse agonist describes the effect on receptor activity rather than where the ligand comes from. So the correct term specifically captures that external, non-body-produced source.