Which statement describes the relationship between binding affinity and receptor occupancy at a given concentration?

Which statement describes the relationship between binding affinity and receptor occupancy at a given concentration?

• A. Lower binding affinity generally leads to greater occupancy
• B. Higher binding affinity generally leads to greater occupancy and a larger response at a given concentration
• C. Binding affinity only affects onset, not occupancy
• D. Binding affinity determines solubility

Answer: (B)

Binding affinity is how tightly a ligand binds to its receptor. At a fixed ligand concentration, the fraction of receptors that are occupied increases with stronger binding (higher affinity, or lower Kd). When a ligand binds more tightly, more receptors are occupied at the same concentration, which usually leads to a larger downstream response because more receptors are engaged to trigger signaling. The reason this is the best statement is that it directly links higher affinity to greater occupancy at the same concentration, and notes the expected bigger response that comes with more receptors being activated. The other ideas don’t fit: lower affinity would not yield greater occupancy at the same concentration; affinity affects occupancy as well as onset, not just onset; and affinity does not determine solubility.

Binding affinity is how tightly a ligand binds to its receptor. At a fixed ligand concentration, the fraction of receptors that are occupied increases with stronger binding (higher affinity, or lower Kd). When a ligand binds more tightly, more receptors are occupied at the same concentration, which usually leads to a larger downstream response because more receptors are engaged to trigger signaling. The reason this is the best statement is that it directly links higher affinity to greater occupancy at the same concentration, and notes the expected bigger response that comes with more receptors being activated. The other ideas don’t fit: lower affinity would not yield greater occupancy at the same concentration; affinity affects occupancy as well as onset, not just onset; and affinity does not determine solubility.