Q.19 Match the following
Group I                                                                 Group II
P) Streptomycin                                             1) Inhibits beta–subunit of RNA polymerase
Q) Cycloheximide                                          2) Inhibits peptidyl transferase activity of 50S subunit
R) Rifamycin                                                  3) Inhibits peptidyl transferase activity of 60S subunit
S) Chloramphenicol                                      4) Inhibits binding of formyl methionine tRNA to ribosome

The correct matching for this CSIR NET-style question pairs antibiotics in Group I with their precise molecular targets in Group II. Streptomycin (P) matches 4, Cycloheximide (Q) matches 3, Rifamycin (R) matches 1, and Chloramphenicol (S) matches 2.​

Matching Solution

P-4, Q-3, R-1, S-2

This pairing reflects established mechanisms from biochemical studies. Each antibiotic disrupts protein synthesis or transcription at specific sites, key for exams like CSIR NET Life Sciences.​

Streptomycin Details

Streptomycin binds irreversibly to the 16S rRNA of the bacterial 30S ribosomal subunit. This interferes with formyl-methionine tRNA binding to the initiation complex, preventing translation start and causing codon misreading. Primarily used against aerobic Gram-negative bacteria and tuberculosis, its action halts protein synthesis in prokaryotes.​

Cycloheximide Details

Cycloheximide targets eukaryotic 80S ribosomes by inhibiting peptidyl transferase on the 60S subunit. It blocks translocation during elongation, arresting ribosomes in the pre-translocation state without affecting prokaryotes. Common in research to halt fungal or eukaryotic protein synthesis.​

Rifamycin Details

Rifamycin binds the beta-subunit of bacterial RNA polymerase, blocking RNA chain elongation after 2-3 nucleotides. This transcription inhibitor spares eukaryotic polymerases, making it vital for tuberculosis treatment. Derivatives like rifampicin define its clinical specificity.​

Chloramphenicol Details

Chloramphenicol binds the 50S ribosomal subunit’s peptidyl transferase center, inhibiting peptide bond formation. It prevents aminoacyl-tRNA accommodation in the A-site, acting bacteriostatically on prokaryotes. Avoided clinically due to side effects like aplastic anemia.​

Exam Relevance

These mechanisms test integration of molecular biology and microbiology for CSIR NET. Bacterial 70S ribosomes (30S/50S) differ from eukaryotic 80S (40S/60S), enabling selective inhibition. Practice such matchings strengthens conceptual recall.​