A nucleic acid is made up of a chain of nucleotides. Each nucleotide consists of a sugar backbone, at least one phosphate group, and a nitrogenous base. AMP has a backbone of the five-carbon sugar ribose, a single phosphate group, and adenine. Adenine is a purine, meaning it has two rings in its structure. The other type of nitrogenous base, the pyrimidines, have a single ring in their structures.