So penicillin consists of three important components. Component number one is the five membered ring we call thiozolidine. So thiozolidine consists of this five member ring here. Now, we also have a fourmember ring here that's called the Betalactum. And it's the instability and the high energy of the beta lactamb that actually gives that penicillin a reactive nature and allows it to actually react in the first place. In fact, it's this red carbon in the betalactam ring that allows it to react as we'll see towards the end of the lecture.