Nucleic acids are polymers of individual nucleotide monomers. Each nucleotide is composed of three parts: a 5-carbon sugar, a phosphate group, and a nitrogenous base. Only two 5-carbon sugars are found in nature: ribose and deoxyribose. Deoxyribose is a ribose derivative in which an oxygen atom is missing from one carbon; the carbon was deoxygenated.