Of the twenty amino acids that make up proteins, six of them have hydrocarbon R-groups . The simplest of the amino acids, glycine, has just a hydrogen atom in the position of the R-group.

Of the twenty amino acids that make up proteins, seven of them have neutral R-groups :

Of the twenty amino acids that make up proteins, six of them have acid or base R-groups . Compare with the simplest of the amino acids, glycine, which has only H as an R-group.