Question

Tetracycline is usually mixed with the culturing medium as selective agents in selecting transformants in gene cloning technique. It acts by:

• A. Inhibiting cell wall formation; inactivated by \(\beta\)-lactamase
• B. Binding to the 30S ribosomal subunit and inhibits the binding of aminoacyl-tRNAs in bacteria
• C. Blocking protein initiation complex formation and causes misreading during translation
• D. Binding to 50S ribosomal subunit and inhibits protein synthesis.

Hint:

For antibiotics used in cloning, remember: Ampicillin/Penicillin \(\rightarrow\) Cell Wall. Tetracycline \(\rightarrow\) 30S ribosome (blocks tRNA binding). Chloramphenicol/Erythromycin \(\rightarrow\) 50S ribosome.

Answer 1

The Correct Option is B

Step 1: Introduction:
Tetracycline, a broad-spectrum antibiotic, is frequently used as a selective marker in molecular cloning. Its efficacy stems from inhibiting a key bacterial process, specifically protein synthesis.
Step 2: Mechanism of Action:
The following analyzes the mechanisms of action for tetracycline and other antibiotics:


(A) Inhibiting cell wall formation; inactivated by \(\beta\)-lactamase: This is characteristic of \(\beta\)-lactam antibiotics such as penicillin and ampicillin, not tetracycline.

(B) Binding to the 30S ribosomal subunit and inhibits the binding of aminoacyl-tRNAs in bacteria: This accurately describes tetracycline's mechanism. It reversibly binds to the bacterial 30S ribosomal subunit, blocking the A-site and preventing aminoacyl-tRNA binding, thus halting protein synthesis elongation.

(C) Blocking protein initiation complex formation and causes misreading during translation: This is the mechanism of aminoglycosides like streptomycin.

(D) Binding to 50S ribosomal subunit and inhibits protein synthesis: This is the mechanism of macrolides (e.g., erythromycin) and chloramphenicol, which target the 50S ribosomal subunit.

Step 3: Conclusion:
Tetracycline functions by binding to the 30S ribosomal subunit, thereby preventing aminoacyl-tRNA attachment.