And finally, the final component of penicillin is this r group. So it's the r group, it's the variable r group that basically gives that penicillin its unique structure. So penicillin is actually a group of many related molecules that all contain the thiozolidine ring, the Betalactum ring, as well as that unique variable r group. Now, how exactly did we discover the fact that penicillin actually acts indirectly on the peptidoglycan cell wall? Well, in the late 1950s, scientists carried out the following experiment. They basically took bacterial cells, they placed them into a hypertonic environment, and then they added penicillin.