Final answer:
The side chain of the beta-lactam molecule in antibiotics determines the spectrum of antibiotic coverage by modifying the properties of the antibiotic and allowing it to target specific types of bacteria.
Step-by-step explanation:
The side chain of the beta-lactam molecule in antibiotics determines the spectrum of antibiotic coverage. The side chain, represented by the variable R group, can be modified chemically to enhance certain properties of the antibiotic, such as absorption, stability, and resistance to enzymatic degradation by beta-lactamases. Different R groups can allow the antibiotic to target a broader range of bacteria, including both gram-positive and gram-negative bacteria, or to specifically target certain types of bacteria.