Final answer:
The β-lactam ring is a four-member cyclic amide found in penicillin and related antibiotics. It is fused to a five-member or six-member ring, depending on the specific antibiotic.
Step-by-step explanation:
The β-lactam ring is a common feature in the structure of penicillin and related antibiotics. It is a four-member cyclic amide, also known as a lactam ring. The ring is fused to a five-member or six-member ring, depending on the specific antibiotic. The structure of the β-lactam ring can be seen in Figure 1.1.8, where it is highlighted in magenta.