Adenine /ˈædᵻnᵻn/ (A, Ade) is a nucleobase (a purine derivative). Its derivatives have a variety of roles in biochemistry includingcellular respiration, in the form of both the energy-rich adenosine triphosphate (ATP) and the cofactors nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD). It also has functions in protein synthesis and as a chemical component ofDNA and RNA. The shape of adenine is complementary to either thymine in DNA or uracil in RNA.
The image right shows pure adenine, as an independent molecule. When connected into DNA, a covalent bond is formed betweendeoxyribose sugar and the bottom left nitrogen, so removing the hydrogen. The remaining structure is called an adenine residue, as part of a larger molecule. Adenosine is adenine reacted with ribose as used in RNA and ATP; deoxyadenosine adenine attached todeoxyribose, as is used to form DNA.