nitrogen
It was known that DNA is composed of nucleotides , each of which contains a nitrogen-containing base, a five-carbon sugar deoxyribose , and a phosphate group. In these nucleotides, there is one of the four possible bases: adenine A , guanine G , cytosine C , or thymine T Figure below . Adenine and guanine are purine bases, and cytosine and thymine are pyrimidine bases.