Nitrogenous bases are organic molecules that play a crucial role in the structure of DNA and RNA. They are classified into two categories: purines and pyrimidines. The purines include adenine and guanine, while the pyrimidines consist of cytosine, thymine, and uracil. These bases pair specifically—adenine with thymine (or uracil in RNA) and guanine with cytosine—forming the rungs of the DNA ladder or the structure of RNA. In addition to their role in genetic material, nitrogenous bases are involved in various biochemical processes. They are essential for the synthesis of nucleotides, which are the building blocks of nucleic acids. The sequence of nitrogenous bases in DNA and RNA encodes genetic information, guiding the synthesis of proteins and influencing cellular functions.