And the final group is a side chain group we also call the R group. Now, the reason we call it an R group is because the R group actually differs from one amino acid to another. And we'll discuss exactly what that means in just a moment. So this is what an alpha amino acid is. It contains the center carbon, that is an alpha carbon, that is, it is attached to this carbon of this carbonyl group, as shown in the following diagram. Now, alphamino acids usually contain a Chiral carbon and the only exception is Glycine, because in Glycine, this R group is a simple H atom.