<prompt> Which of the followig antitubercular drug acts by inhibiting bacterial DNA dependent RNA polymerase?ChloramphenicolErythromycinTetracyclinesRifampicin  <response>: Ans. D. Rifampicin. Ref. KDT 6thpg. 741, 745.KDT 6thpg. 741...Rifampicin inhibits DNA dependent RNA synthesis. Probably the basis of selective toxicity is that mammalian RNA polymerase does not avidly bind rifampin. ANTIBIOTICMECHANISM OF ACTIONAminoglycosides Inhibit protein synthesis by binding to a portion of the bacterial ribosome. Most of them are bacteriocidal i.e., cause bacterial cell death.Bacitracin Inhibits cell wall production by blocking the step in the process recycling of the membrane lipid carrier which is needed to add on new cell wall subunits.Beta-lactam antibiotics A name for the group of antibiotics which contain a specific chemical structure i.e., a beta-lactam ring. This includes penicillins, cephalosporins, carbapenems and monobactams.Cephalosporins Similar to penicillins in their mode of action but they treat a broader range of bacterial infections. They have structural similarities to penicillins and many people with allergies to penicillins also have allergic reactions to cephalosporins.Chloramphenicol Inhibits protein synthesis by binding to a subunit of bacterial ribosomes 50S.Glycopeptides e.g., vancomycin Interferes with cell wall development by blocking the attachment of new cell wall subunits muramyl pentapeptides.Macrolides e.g., erythromycin and Lincosamides e.g., clindamycin inhibiting bacterial protein synthesis. It combines with 50S ribosome subunits and interferes with translocation.Penicillins Inhibits formation of the bacterial cell wall by blocking cross-linking of the cell wall structure. The cell wall is a needed protective casing for the bacterial cell.Quinolones Blocks DNA synthesis by inhibiting one of the enzymes DNA gyrase needed in this process.Rifampin Inhibits RNA synthesis by inhibiting one of the enzymes DNA-dependent RNA polymerase needed in this process. RNA is needed to make proteins.Tetracyclines Inhibit protein synthesis by binding to the subunit of the bacterial ribosome 30S subunit.Trimethoprim and Sulfonamides Blocks cell metabolism by inhibiting enzymes which are needed in the biosynthesis of folic acid which is a necessary cell compound. 