Discussion

Match the antibiotics in Group I with their mechanism of action in Group II

Group I	Group II
P. Tetracyclines	1. Inhibits bacterial protein synthesis by blocking peptidyl transfer
Q. Chloramphenicol	2. Inhibits bacterial protein synthesis by blocking the A-site on the ribosome
R. Cycloheximide	3. Misreads the genetic code and inhibits initiation of protein synthesis
S. Streptomycin	4. Inhibits protein synthesis by blocking peptidyl transferase on 80S ribosome

Answer: B

The correct match is P-2, Q-1, R-4, S-3.

Tetracyclines bind the 30S subunit and block aminoacyl-tRNA from entering the A site (P-2).
Chloramphenicol binds the 50S subunit and inhibits peptidyl transferase, so peptide bonds cannot form (Q-1).
Cycloheximide acts on eukaryotic 80S ribosomes, blocking translocation at the peptidyl transferase centre, and does not affect bacteria (R-4).
Streptomycin binds the 30S subunit, causes misreading of the code and interferes with initiation (S-3).

Option A swaps cycloheximide and streptomycin, and C and D misplace tetracycline, which acts at the A site.

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