Nucleotides: Structure, Components, and Role in DNA & RNA

A nucleotide is an organic molecule that is the basic building block of nucleic acids. Nucleotides are composed of three parts: a sugar group, a phosphate group, and a nitrogenous base. The sugar group is either ribose or deoxyribose, the phosphate group is a phosphoric acid residue, and the nitrogenous base is one of four types: adenine, thymine, guanine, or cytosine. Nucleotides are linked together by covalent bonds to form polynucleotides, which are polymers that make up the genetic material of all living organisms.