Question

Which of the following statements are True?
A. Tetracycline inhibits protein synthesis through interference with the binding of aminoacyl-tR to 30S subunit of ribosome
B. Chloramphenicol inhibits protein synthesis by combining with the 50S subunit of ribosome
C. Erythromycin inhibits protein synthesis by binding on the 30S subunit of ribosome
D. Streptomycin inhibits protein synthesis by combining with 30S subunit of ribosome

• A. A and C Only
• B. A and D Only
• C. A, B and D Only
• D. C and D Only

Hint:

Remember ribosome targets:
30S Inhibitors: Tetracycline, Aminoglycosides (Streptomycin) [Mnemonic: AT 30].
50S Inhibitors: Chloramphenicol, Erythromycin, Lincosamides [Mnemonic: CLEan at 50].

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify the correct statements regarding the specific ribosomal subunit target sites and mechanisms of action of major antibacterial translation inhibitors.

Step 2: Key Formula or Approach:
Antibiotics target prokaryotic 70S ribosomes (30S and 50S subunits):
• 30S Subunit Inhibitors: Tetracycline, Aminoglycosides (Streptomycin, Kamycin).

• 50S Subunit Inhibitors: Chloramphenicol, Macrolides (Erythromycin), Lincosamides.

Step 3: Detailed Explation:

• Statement A (True): Tetracyclines reversibly bind to the 30S ribosomal subunit, sterically blocking incoming aminoacyl-tR from accessing the A-site.

• Statement B (True): Chloramphenicol binds to the 50S ribosomal subunit and inhibits peptidyl transferase activity, preventing peptide bond formation.

• Statement C (False): Erythromycin (a macrolide) binds to the 50S subunit (not 30S) near the peptidyl transferase center, blocking ribosome translocation along mR. Thus, C is incorrect.

• Statement D (True): Streptomycin (an aminoglycoside) binds to the 30S ribosomal subunit (specifically 16S rR), causing misreading of genetic code and inhibiting translation initiation.

Step 4: Fil Answer:
Statements A, B, and D are true, making Option (C) correct.