What occurs when erythromycin binds to the large subunit of the bacterial ribosome?

• A. It promotes the transfer of tRNA from the E site to the P site.
• B. It blocks the transfer of tRNA from the A site to the P site.
• C. It allows tRNA to move freely between all sites.
• D. It prevents tRNA binding at the E site.

Answer: (B)

When erythromycin binds to the large subunit of the bacterial ribosome, it specifically interferes with the process of translation. This antibiotic works by inhibiting the bacterial ribosome's ability to translocate tRNA between the aminoacyl (A), peptidyl (P), and exit (E) sites.

The correct answer reflects how erythromycin effectively blocks the transfer of tRNA from the A site to the P site. This action disrupts the synthesis of proteins by preventing the formation of peptide bonds between amino acids, thereby stalling the translation process. The antibiotic binds to the ribosomal RNA in the large subunit, which inhibits the necessary conformational changes required for tRNA movement.

As a result, ribosomal function is compromised, halting protein production that is crucial for bacterial growth and survival. This mechanism is why erythromycin is used to combat bacterial infections.