This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Antibiotics, Subject name: Pharmacology
The most impoant mechanism by which tetracycline antibiotics exe antimicrobial action 
Select and explain. 
A. They interfere with DNA mediated RNA synthesis in bacteria, B. They bind to 50S ribosomes and interfere with translocation of the growing peptide chain in the bacteria, C. They bind to 30S ribosomes and inhibit bacterial protein synthesis, D. They chelate Ca2+ ions and alter permeability of bacterial cell membrane
C: They bind to 30S ribosomes and inhibit bacterial protein synthesis
Answer: C: They bind to 30S ribosomes and inhibit bacterial protein synthesis 
Explanation: TETRACYCLINES Mechanism of action:- The tetracyclines are primarily bacteriostatic; inhibit protein synthesis by binding to 30S ribosomes in susceptible organism. Subsequent to such binding, attachment of aminoacyl-t-RNA to the acceptor (A) site of mRNA-ribosome complex is interferred as a result, the peptide chain fails to grow. The sensitive organisms have an energy dependent active transpo process which concentrates tetracyclines intracellularly. In gram-negative bacteria tetracyclines diffuse through porin channels as well. Ref:- kd tripathi; pg num:-733