This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti Microbial, Subject name: Pharmacology
Tetracycline inhibits protein synthesis by- 
Select and explain. 
A. Inhibiting initiation and causing misreading of mRNA, B. Binding to 30 S subunit and inhibits binding of aminoacyltRNA, C. Inhibiting peptidyitransferase activity, D. Inhibiting translocation
B: Binding to 30 S subunit and inhibits binding of aminoacyltRNA
Answer: B: Binding to 30 S subunit and inhibits binding of aminoacyltRNA 
Explanation: Ans. is 'b' i.e., Binding to 30 S subunit and inhibits binding of ami noacyl tRNA Tetracyclineso Tetracyclines are classified into three groups -# Group 1 - Tetracycline, oxytetracycline, chlortetracycline.# Group II - Lymecycline, Demeclocycline.# Group III - Minocycline, Doxycycline.o Tetracyclines are bacteriostatic and broad spectrum antibiotics.o Tetracycline interact with small ribosomal subunits, blacking access of aminoacyl- tRNA to the nuRNA-ribos- ome complex.o Oral absorption of tetracyclines is impaired by food except doxycycline and minocycline which are absorbed completely irrespective of food.o Most tetracyclines are primarily excreted in urine by glomerular filtration; dose has to be reduced in renal failure; doxycycline is an exception - doxycycline can be used in renal failure.o Tetracyclines can cross placenta and secreted in milk - contraindicated during pregnancy and lactation.