Which statement describes how binding affinity relates to receptor occupancy?

• A. Binding affinity determines color of the drug
• B. Binding affinity determines the concentration needed to achieve significant receptor occupancy
• C. Binding affinity determines packaging
• D. Binding affinity determines taste

Answer: (B)

Binding affinity describes how tightly a drug binds to its receptor, and receptor occupancy is how many receptors are actually bound by the drug at a given concentration. The key link is the law of mass action: the fraction of receptors occupied depends on the drug concentration relative to the dissociation constant (KD). A high-affinity drug (low KD) achieves significant occupancy at a lower concentration, while a low-affinity drug (high KD) requires a higher concentration to reach the same occupancy. So binding affinity directly sets the concentration needed to achieve meaningful receptor occupancy, which is why this statement is the best choice. The other properties—color, packaging, and taste—do not describe occupancy or how tightly the drug binds to receptors.