Exogenous ligand is defined as what?

Exogenous ligand is defined as what?

• A. Drug; any substance not produced by the body that selectively binds to a receptor
• B. Substance produced within the body that binds to a receptor
• C. Substance not produced by the body that non-selectively binds to receptors
• D. A ligand that only binds to enzymes

Answer: (A)

Exogenous ligands are substances that come from outside the body and can interact with receptors to produce a response. The best answer captures this external origin and the receptor-target action, using the common example of a drug. So a substance not produced by the body that binds to a receptor is an exogenous ligand, and drugs are classic examples of them. The other ideas miss the essential point: endogenous ligands are made inside the body and bind receptors; exogenous ligands don’t have to be non-selective—many are selective for specific receptors; and binding to enzymes isn’t the defining feature of an exogenous ligand.

Exogenous ligands are substances that come from outside the body and can interact with receptors to produce a response. The best answer captures this external origin and the receptor-target action, using the common example of a drug. So a substance not produced by the body that binds to a receptor is an exogenous ligand, and drugs are classic examples of them.

The other ideas miss the essential point: endogenous ligands are made inside the body and bind receptors; exogenous ligands don’t have to be non-selective—many are selective for specific receptors; and binding to enzymes isn’t the defining feature of an exogenous ligand.