Adenine is one of the four nitrogen-containing base pairs found in DNA, the others being Cytosine (C), Guanine (G) and Thymine (T). It is one of the purines (the other being guanine). Both cytosine and thymine are pyrimidines. Adenine has a molecular weight of ~135 g/mol. In DNA it provides stability to the double helix by forming two hydrogen bonds with thymine, which is adenine's complementary base pair. However in RNA it forms hydrogen bonds with uracil instead of thymine. Purines are 6-membered rings attatched to a 5-membered ring with nitrogens at positions 1, 3, 7 and 9 on the rings.