Nucleic acids are targets for several important drugs, including various anti microbial and anticancer agents. There are two types of nucleic acid – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). One binding region consists of three nucleic acid bases, which are complementary to a specific triplet of nucleic acid bases on messenger RNA (mRNA), while the other binding region recognizes a specific amino acid. The tricyclic system is the correct size to be inserted and can interact with the nucleic acid bases by van der Waals interactions. Reaction of an alkyl halide with a nucleophilic group on DNA results in a nucleophilic substitution reaction where the nucleophile displaces the halide and forms a covalent bond with the drug. The rationale is that the synthetic oligonucleotide should bind to the complimentary segment of mRNA by base pairing. Ribosomal RNA is the target for some important antibacterial agents such as streptomycin, the tetracyclines, chloramphenicol and erythromycin.