Which ligand has a higher binding affinity based on the affinity curve?

The correct choice indicates that Ligand 1 has a higher binding affinity compared to Ligand 2. This conclusion is derived from examining the affinity curve, which is a graphical representation demonstrating how different concentrations of ligands influence the binding to a target, such as a protein or receptor.

In such curves, the binding affinity is typically reflected in the shape and position of the curve. A ligand with a higher affinity will shift the curve to the left, meaning that it can achieve half-maximal binding at a lower concentration compared to a ligand with lower affinity, which would show a curve shifted to the right. Thus, evaluating the curve shows that Ligand 1 binds more effectively at lower concentrations, indicating a stronger interaction with the target.

In contrast, if Ligand 2 were to have higher or equal affinity, the curve corresponding to it would either overlap with or lie to the left of Ligand 1’s curve. If both ligands were ineffective, the curves would show minimal binding, which would not apply in this case since we are assessing their relative affinities. Hence, the observations of the affinity curve clearly support the identification of Ligand 1 as having the higher binding affinity.