MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A patient with a severe bacterial infection is prescribed a new antibiotic that specifically targets the 50S ribosomal subunit. Which of the following processes would be directly inhibited in the bacterial cells by this antibiotic?
- ADNA replication
- BTranscription
- CCell wall synthesis
- DProtein synthesis
Show answer & explanationAnswer & explanation
Correct answer: D. Protein synthesis
Ribosomes, composed of ribosomal RNA (rRNA) and proteins, are the cellular machinery responsible for protein synthesis (translation). In bacteria, ribosomes consist of a 30S and a 50S subunit that combine to form a 70S ribosome. An antibiotic targeting the 50S subunit would directly interfere with the assembly or function of the bacterial ribosome, thereby inhibiting protein synthesis.
Why the other options are wrong
- A. DNA replication involves DNA polymerases and other enzymes that act on DNA, not directly on ribosomal subunits.
- B. Transcription is the process of synthesizing RNA from a DNA template, carried out by RNA polymerase, not ribosomes.
- C. Cell wall synthesis involves enzymes that build peptidoglycan layers, which is a different pathway from ribosome function.
Bacterial Ribosomes
Prokaryotic ribosomes (70S) composed of a 30S and a 50S subunit, responsible for protein synthesis. They are a common target for antibiotics due to their structural differences from eukaryotic ribosomes.
- 70S ribosome (prokaryotic).
- Subunits: 30S and 50S.
- Site of protein synthesis (translation).
- Structurally distinct from eukaryotic (80S) ribosomes.
Memory trick: Ribosomes: 'P'rotein 'P'roduction 'P'lant!