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: Understanding the Concept:
Tetracycline is a broad-spectrum antibiotic commonly used as a selective agent in molecular cloning. Its effectiveness relies on a specific mechanism of action that targets a vital process in bacteria, typically protein synthesis.
Step 2: Detailed Explanation:
Let's analyze the mechanism of action of tetracycline and other antibiotics mentioned in the options:


(A) Inhibiting cell wall formation; inactivated by \(\beta\)-lactamase: This describes the mechanism of \(\beta\)-lactam antibiotics like penicillin and ampicillin, not tetracycline.

(B) Binding to the 30S ribosomal subunit and inhibits the binding of aminoacyl-tRNAs in bacteria: This is the correct mechanism for tetracycline. It binds reversibly to the 30S subunit of the bacterial ribosome, which physically blocks the A-site. This prevents charged tRNA molecules (aminoacyl-tRNAs) from binding, thereby halting the elongation step of protein synthesis.

(C) Blocking protein initiation complex formation and causes misreading during translation: This describes the action of aminoglycoside antibiotics like streptomycin.

(D) Binding to 50S ribosomal subunit and inhibits protein synthesis: This describes the action of macrolide antibiotics (like erythromycin) and chloramphenicol, which target the larger 50S ribosomal subunit.

Step 3: Final Answer:
Tetracycline acts by binding to the 30S ribosomal subunit and preventing the attachment of aminoacyl-tRNA.