Final answer:
Penicillin kills bacteria by inhibiting the enzyme transpeptidase necessary for cell wall synthesis, leading to the bacterial cell bursting. Semisynthetic derivatives like methicillin provide resistance to penicillinase, an enzyme that some bacteria produce to neutralize penicillin. Despite its efficacy, some individuals are allergic to penicillin.
Step-by-step explanation:
Penicillin, a member of the ß-lactam class of antibiotics, is effective in treating bacterial infections by interfering with the synthesis of the bacteria's cell wall. This process involves the inhibition of a bacterial enzyme called transpeptidase, which normally catalyzes the final step in cell-wall biosynthesis. Because penicillin disrupts this crucial step, the bacteria cannot properly form their cell wall, resulting in the cell taking up too much water and eventually bursting. This mode of action is specific to bacteria because, unlike bacterial cells which have cell walls, human cells only have cell membranes and are thus spared from the effects of penicillin. Semisynthetic derivatives of penicillin have been developed to overcome bacterial resistance that arises through the production of penicillinase, an enzyme that deactivates the antibiotic. Newer penicillins, like methicillin, have modified R groups which protect the ß-lactam ring from penicillinase, thereby extending their effectiveness against resistant strains of bacteria. It is important to note that some individuals may be allergic to penicillin, and therefore alternative antibiotics must be used when treating these individuals. Advancements in the field continue as scientists strive to stay ahead in the arms race against antibiotic-resistant bacteria.