Nucleotides are the basic building blocks of nucleic acids (both DNA & RNA) Structurally, nucleotides have 3 components. v A nucleotide consists of a sugar molecule (either ribose in RNA or deoxyribose in DNA) attached to a phosphate group and a nitrogen-containing base. The bases used in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T). In RNA, the base uracil (U) takes the place of thymine. v The molecule without the phosphate group is called a nucleoside.