Adenine

Adenine is a purine with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate (ATP) and the cofactors nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD), and protein synthesis, as a chemical component of DNA and RNA.

Structure
It forms several tautomers, compounds that can be rapidly interconverted and are often considered equivalent.

Biosynthesis
The Purine metabolism involves the formation of Adenine and Guanine. Both adenine and guanine are derived from the nucleoside inosine monophosphate (IMP), which is synthesised on a pre-existing ribose through a complex pathway using atoms from the amino acids glycine, glutamine, and aspartic acid, as well as formate ions transferred from the coenzyme tetrahydrofolate.

Function
Adenine is one of the two purine nucleobases used in forming nucleotides of the nucleic acids. In DNA, adenine binds to thymine via two hydrogen bonds to assist in stabilizing the nucleic acid structures. In RNA, which is used in the cytoplasm for protein synthesis, adenine binds to uracil.

Adenine forms adenosine, a nucleoside, when attached to ribose, and deoxyadenosine when attached to deoxyribose. It forms adenosine triphosphate (ATP), a nucleotide, when three phosphate groups are added to adenosine. Adenosine triphosphate is used in cellular metabolism as one of the basic methods of transferring chemical energy between chemical reactions.

History
In older literature, adenine was sometimes called Vitamin B 4 . It is no longer considered a true vitamin nor part of the Vitamin B complex. However, two B vitamins, niacin and riboflavin, bind with adenine to form the essential cofactors nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD) respectively.

Some think that, at the origin of life on Earth, the first adenine was formed by the polymerization of five hydrogen cyanide (HCN) molecules. However, this has been criticized by some chemists.