Why is the beta-lactam ring essential to the activity of beta-lactam antibiotics?

• A. Because it acts as a rigid hydrophobic anchor that inserts into the cytoplasmic membrane and blocks nutrient transport channels essential for cell viability.
• B. It chelates divalent metal cofactors in autolytic enzymes causing those enzymes to hyperactivate and digest cell wall components independent of PBPs.
• C. It mimics the D-Ala-D-Ala substrate of PBPs, enabling covalent binding and inhibition of the cross-linking enzymes; cleavage of this ring by beta-lactamase abolishes activity.
• D. Because it is the principal determinant of oral bioavailability by protecting the molecule from first-pass hepatic metabolism, explaining why versions without it are rapidly cleared.

Answer: (C)