A nucleotide is the basic building block of DNA and RNA. Each nucleotide consists of three components: a nitrogenous base (adenine, thymine, cytosine, or guanine in DNA; adenine, uracil, cytosine, or guanine in RNA), a five-carbon sugar (deoxyribose in DNA and ribose in RNA), and a phosphate group. Nucleotides link together to form the long chains of DNA and RNA, encoding genetic information.