The story of Thalidomide and its effects on birth defects is a good story about the chirality of molecules and their significance. The same molecule on 2d paper suddenly becomes a teratogen when the racemic mixture is given (50/50 mix of the “right hand” and “left hand” versions.) When a simple molecule like this drug with only a single chiral center at the base of so many issues, imagine a protein with hundreds or thousands of chital centers and the potential effects (or lack of effect at all) with simple changes.
I'd just like to recommend against using thalidomide as an example of chiral effects. Rather unusually, thalidomide has a nitrogen atom as its chiral center. As such, it rapidly racemizes (interconverts) at physiological pH. This makes the claim of stereospecific teratogenicity a bit puzzling as it shouldn't be possible to resolve by administering enantiopure thalidomide.
The mechanistic story of thalidomide is a bit complicated. Ultimately the mouse and rat models used couldn't possibly predict teratogencitiy as these models have an amino acid mutation (valine -> isoleucine) that prevents binding of thalidomide to Cereblon, the protein that mediates thalidomide's teratogencitiy [0]. Amazingly, although this story is oft-repeated, its origins are unclear. This is likely the origin of the myth [1], but knowing what we know now these results should be impossible.
