This is the only part of a dna/rna nucleotide that changes. it is found along with the 5-carbon sugar and the phosphate group.

The appropriate response is Nitrogenous Base. It is just a nitrogen containing atom that has an indistinguishable concoction properties from a base. They are especially vital since they make up the building pieces of DNA and RNA: adenine, guanine, cytosine, thymine and uracil.