Adenine

Ball-and-stick Stick Space-filling

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15 atoms, 16 bonds.

IUPAC name: 7H-purin-6-amine
Molar mass: 135.130(16) g/mol
Atoms: 15
SMILES: C1=NC2=NC=NC(=C2N1)N
InChIKey: GFFGJBXGBJISGV-UHFFFAOYSA-N
PubChem CID: 190

Made of

Structural formula of adenine. Each unlabelled corner is a carbon atom, and the two hydrogens on carbon are not drawn. It shows which atoms are joined to which, not the shape. The model above shows the shape.

Adenine is the A of DNA and RNA, and a part of ATP (adenosine triphosphate). It is a purine, two fused rings of carbon and nitrogen, with an amino group (NH₂) on carbon 6. ChEBI, a database of small molecules of biological interest, classes it as the parent compound of the 6-aminopurines. Five carbon, five nitrogen and five hydrogen atoms make it up, and a mole weighs 135.13 g. Its IUPAC (International Union of Pure and Applied Chemistry) name, 7H-purin-6-amine, fixes which ring nitrogen carries a hydrogen in the model.

The NCI Thesaurus, the US National Cancer Institute’s reference vocabulary, calls adenine the precursor of adenosine and deoxyadenosine. The National Human Genome Research Institute (NHGRI) defines a nucleotide as a base bearing nitrogen, a sugar and a phosphate group joined together. Its sugar is ribose in RNA and deoxyribose in DNA. MeSH, the US National Library of Medicine’s subject vocabulary, describes adenine as a fundamental unit of the adenine nucleotides.

Structure and bonding

Adenine’s two rings share one edge. A six-membered ring of four carbons and two nitrogens is fused along a carbon–carbon bond to a five-membered ring of three carbons and two nitrogens. With Labels on, the amino group shows as an N with two H atoms on a carbon of the larger ring. A single H sits on the smaller ring’s nitrogen next to the shared carbon, the 7H of the name. The US Environmental Protection Agency’s Toxic Substances Control Act (TSCA) inventory lists adenine as 9H-purin-6-amine instead, and Australia’s industrial chemicals inventory as 1H-purin-6-amine.

Turned edge-on, the model collapses to a line: PubChem’s computed 3D model puts all 15 atoms in one plane. The Stick view draws three C=N double bonds and one C=C double bond, fixed in place between single bonds. Yet the six-membered ring’s C–N bonds measure about 1.35 Å (a ten-billionth of a metre) in the model whether drawn single or double.

Chem1 describes the π bonds of a conjugated ring like benzene, one of alternating single and double bonds, as delocalised: spread over the ring, not held between two atoms. In the Space-filling view the spheres merge into one flat plate.

Where it turns up

Adenine turns up wherever there is DNA or RNA. NHGRI counts it among the four bases of DNA, with cytosine, guanine and thymine. RNA uses the same set except that uracil takes thymine’s place. One copy of the human genome runs to about 3 billion base pairs across 23 chromosomes, and every A–T pair among them holds one adenine.

The free base is a metabolite as well, a substance made or used in an organism’s chemistry. ChEBI records it in humans, mice, the yeast Saccharomyces cerevisiae, the bacterium Escherichia coli and Daphnia magna. The LOTUS database of natural products reports it in Streptomyces piomogenus and Bridelia balansae, among other organisms. Bound into ATP, adenine is present in all living cells, according to the NCI Thesaurus entry for that nucleotide. As a commercial chemical, adenine is registered under REACH, the European Union’s chemicals registration law, and listed as active on the TSCA inventory.

Why it matters

In DNA adenine pairs with thymine and in RNA with uracil, according to NHGRI. The two strands of the helix are held together by hydrogen bonds, which Chem1 treats as the most important case of dipole–dipole attraction. That is the pull of one polar molecule’s positive end on another’s negative end. Each links a nitrogen on one chain to a nitrogen or oxygen on the base opposite, and the A–T pair is usually drawn with two of them.

Efficient hydrogen bonding across the helix is possible only for A with T and C with G, Chem1 explains, so these two pairs form the alphabet that carries genetic information. The bases face each other inside the helix, with the backbones outside. Base pairing is not the only support: water molecules hydrogen-bonded to the helix’s outer surface also help hold it steady, in Chem1’s account.

ATP carries adenine into metabolism. The NCI Thesaurus links adenosine triphosphate to energy production for metabolic processes and to RNA synthesis. ATP also acts as a neurotransmitter, according to MeSH and the NCI Thesaurus.

Properties

Properties of adenine Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 190.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₅H₅N₅
Molar mass	135.130(16) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	5
Hydrogen atoms	5
Nitrogen atoms	5
Bonds	16
Single bonds	12
Double bonds	4
PubChem molecular weight	135.13 g/mol	g/mol	PubChem

Safety

As a purified chemical, adenine is classified as toxic if swallowed. In 96.8% of 349 reports from 10 notifications to the European Chemicals Agency (ECHA), companies classified it as toxic if swallowed, and the aggregated label carries the signal word Danger. The classification concerns the purified substance, not the adenine bound into the nucleic acids of living things. The PubChem Laboratory Chemical Safety Summary for adenine is the authoritative sheet.

Questions

What does adenine pair with in DNA and RNA?

In DNA adenine pairs with thymine, and in RNA its partner is uracil, according to the NHGRI genetics glossary. The glossary adds that the adenine–thymine pair is usually represented with two hydrogen bonds. Since one base fixes the other, NHGRI notes, a DNA sequence can be reported for one strand only; the partner strand follows from it.

What is the difference between adenine and guanine?

Both are purines, built from two fused rings of carbon and nitrogen, but guanine has one more atom. Adenine is C₅H₅N₅ and guanine C₅H₅N₅O. Adenine carries its amino group on carbon 6, while guanine's IUPAC name, 2-amino-1,7-dihydropurin-6-one, puts the amino group on carbon 2 and an oxygen on carbon 6. In DNA, adenine pairs with thymine and guanine with cytosine.

Is adenine the same thing as adenosine or ATP?

No. Adenine is the base on its own, and the NCI Thesaurus calls it the precursor of the nucleosides adenosine and deoxyadenosine. ATP, adenosine triphosphate, goes further: MeSH describes it as an adenine nucleotide whose sugar carries three phosphate groups. So adenine is one piece of ATP, joined there to ribose and the phosphate chain, while the free base has no phosphate at all.

Which organisms contain adenine?

Every organism that stores its genes in DNA or RNA. NHGRI counts adenine among the four bases of DNA and of RNA, where uracil replaces thymine. The free base also occurs on its own: ChEBI records it as a metabolite of the bacterium Escherichia coli, among other organisms.

Made of the same elements

C₃H₆N₆ Melamine 15 atoms, 15 bonds.
C₅H₉N₃ Histamine 17 atoms, 17 bonds.
C₄H₁₁N₅ Metformin 20 atoms, 19 bonds.
(CH₃)₃N Trimethylamine 13 atoms, 12 single bonds.
C₁₀H₁₄N₂ Nicotine 26 atoms, 27 bonds.