Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): Tetracyclines inhibit protein synthesis and exhibit broad spectrum bactericidal effect.
Reason (R): Tetracyclines bind to 30 S subunit and inhibit the binding of aminoacyl-tRNA to A-site.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

A classic exam trap is confusing bacteriostatic and bactericidal drugs:
Bacteriostatic: Tetracyclines, Macrolides, Sulfonamides, Chloramphenicol.
Bactericidal: Penicillins, Cephalosporins, Aminoglycosides, Fluoroquinolones.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Tetracyclines are widely used antibiotics in veterinary medicine.
We must evaluate their primary spectrum classification (bacteriostatic vs. bactericidal) and molecular mechanism of action.
Detailed Explanation:
- Assertion (A) Evaluation: While tetracyclines are indeed broad-spectrum antibiotics, they are classified as bacteriostatic agents, not bactericidal.
They inhibit bacterial cell growth and replication but do not directly kill the bacteria; clearance of the infection depends on the host's immune system. Thus, Assertion (A) is false.
- Reason (R) Evaluation: Tetracyclines exert their effect by entering bacterial cells and reversibly binding to the 30S ribosomal subunit.
This binding blocks the access of the aminoacyl-tRNA to the ribosomal acceptor (A) site, preventing the addition of new amino acids to the growing peptide chain and inhibiting protein synthesis. Thus, Reason (R) is true.
Therefore, Assertion (A) is false but Reason (R) is true.

Step 2: Final Answer:
The correct option is (D).