MCAT® ExamBiological and Biochemical Foundations of Living SystemsEasy
A research team is investigating a novel antibiotic. They observe that this antibiotic specifically targets bacterial ribosomes, preventing the formation of peptide bonds between amino acids during protein synthesis. Which enzymatic activity is directly inhibited by this antibiotic?
- AAminoacyl-tRNA synthetase activity
- BPeptidyl transferase activity
- CRNA polymerase activity
- DDNA ligase activity
Show answer & explanationAnswer & explanation
Correct answer: B. Peptidyl transferase activity
The formation of peptide bonds during protein synthesis (translation) is catalyzed by peptidyl transferase, an enzymatic activity intrinsic to the large ribosomal subunit. Inhibiting this activity would directly prevent peptide bond formation.
Why the other options are wrong
- A. Aminoacyl-tRNA synthetase is responsible for attaching the correct amino acid to its corresponding tRNA, which occurs before peptide bond formation.
- C. RNA polymerase is involved in transcription (DNA to RNA), not translation (protein synthesis).
- D. DNA ligase is involved in DNA replication and repair, not protein synthesis.
Peptidyl Transferase
The enzymatic activity, residing in the ribosomal large subunit, responsible for catalyzing the formation of peptide bonds between incoming amino acids during protein synthesis (translation).
- Catalyzes peptide bond formation.
- Part of the large ribosomal subunit.
- Is a ribozyme (RNA molecule with catalytic activity).
- Essential for polypeptide chain elongation.
Memory trick: Peptidyl Transferase: Makes the Peptides, Transfers the chain!