Binding of a ligand to its receptor can be shown in a graph. Ligands can also attach to other binding sites than the receptor (e.g. other proteins). This is called non-specificor aspecific binding.
An increasing concentration of ligand [L] is plotted against the bound ligand. The total binding (pink line) is not equal to the ligand-receptor complex [LR] (black line), but is the sum of the specific ([LR]) and non-specific binding (green line). Actually, the specific binding is usually calculated by subtracting the non-specific binding from the total binding.
The curve of the specific binding approaches a maximum, when all receptors are occupied (saturated). The non-specific binding is binding of the ligand to molecules other than the receptor.
The receptors below represent the situation at 3 different ligand concentrations. Specific binding of ligand to the receptor (black) increases with increasing ligand concentration. The same is true for unspecific binding of the ligand (green). At a very low ligand concentration (1) the degree of specific and unspecific binding is almost the same. At high ligand concentration (3), the receptors are saturated and specific binding is maximal, whereas unspecific binding still increases.