MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A research team is investigating a novel antibiotic that targets bacterial protein synthesis. They discover that this antibiotic specifically binds to the 50S ribosomal subunit of prokaryotic cells, preventing the formation of peptide bonds. This action directly inhibits which enzymatic activity?
- APeptidyl transferase
- BRNA polymerase
- CAminoacyl-tRNA synthetase
- DDNA gyrase
Show answer & explanationAnswer & explanation
Correct answer: A. Peptidyl transferase
The formation of peptide bonds during protein synthesis is catalyzed by the peptidyl transferase activity, which is an intrinsic ribosomal enzymatic function located in the 50S subunit of prokaryotic ribosomes.
Why the other options are wrong
- B. RNA polymerase synthesizes RNA from a DNA template (transcription), not protein synthesis.
- C. Aminoacyl-tRNA synthetase charges tRNAs with their cognate amino acids, a step prior to ribosomal action.
- D. DNA gyrase is involved in DNA replication and transcription by relieving supercoiling, not protein synthesis.
Peptidyl Transferase Activity
Peptidyl transferase is the enzymatic activity of the ribosome (a ribozyme) responsible for catalyzing the formation of peptide bonds between amino acids during protein synthesis.
- Located in the large ribosomal subunit (50S in prokaryotes, 60S in eukaryotes).
- Forms the peptide bond between the growing polypeptide chain and the incoming amino acid.
- It is a ribozyme, meaning the RNA component of the ribosome has the catalytic activity.
Memory trick: Ribosomes are the 'PEPTIDE' factories.