Question

The antibiotic not associated with inhibition of protein synthesis is

• A. Chloromycetin
• B. Tetracycline
• C. Puromycin
• D. Penicillin

Answer 1

The correct option is D Penicillin

Puromycin is a fungal antibiotic which is made by the mold Streptomyces alboniger. It has the structural analogy with 3' end of an aminoacyl-tRNA which binds to A site of the ribosome. Thus, the antibiotic binds to the ribosomal A site. Peptide bond formation produces peptidyl-puromycin and dissociates from the ribosome which in turn prematurely terminates polypeptide synthesis. Tetracyclines block the A site on the ribosome, thereby preventing the binding of aminoacyl-tRNAs and finally inhibit protein synthesis. Chloromycetin blocks peptidyl transfer and thereby inhibits protein synthesis. Bacterial cell walls have a heteropolymer of alternating N-acetylglucosamine and N-acetylmuramic acid residues which are cross-linked by short peptides. The peptide cross-links make a strong sheath that shields the entire cell and prevents cellular swelling and lysis due to the osmotic entry of water. Penicillin kills bacteria by inhibiting synthesis of the cross-links and making cell wall too weak to resist osmotic lysis. The correct answer is D.