Answer
The two enantiomers of dopa have very different shapes, even if they have the same number of atoms of each element involved and have the same ones connected to one another. The great difference in activity shows that the key thing in determining biological activity is shape, not merely the number or arrangement of atoms.
Work Step by Step
The image in the textbook next to the question makes the shape difference very clear, so this must be the reason for the difference in activity.
