Final answer:
Erythromycin inhibits protein synthesis by binding to the 50 S ribosomal subunits of microorganisms, preventing the assembly of amino acids into proteins.
Step-by-step explanation:
Erythromycin inhibits protein synthesis by binding to the 50 S ribosomal subunits in microorganisms. This binding prevents the ribosome from assembling the amino acids into a growing protein chain, ultimately inhibiting the synthesis of proteins necessary for the microorganism's survival. However, it's important to note that humans do not have 50 S ribosomal subunits, so erythromycin is not effective against human cells.