Guanine

Ball-and-stick Stick Space-filling

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16 atoms, 17 bonds.

IUPAC name: 2-amino-1,7-dihydropurin-6-one
Molar mass: 151.129(17) g/mol
Atoms: 16
SMILES: C1=NC2=C(N1)C(=O)NC(=N2)N
InChIKey: UYTPUPDQBNUYGX-UHFFFAOYSA-N
PubChem CID: 135398634

Made of

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

Two fused rings of carbon and nitrogen, carrying an amino group and a double-bonded oxygen, make up guanine. The National Human Genome Research Institute (NHGRI) lists it as one of the four nucleotide bases of DNA, beside adenine, cytosine and thymine. ChEBI, a database of biological chemicals, classes it as a 2-aminopurine carrying a 6-oxo group: a purine frame bearing an amino group, NH₂, and a double-bonded oxygen. Its IUPAC (International Union of Pure and Applied Chemistry) name is 2-amino-1,7-dihydropurin-6-one.

Five carbon, five hydrogen and five nitrogen atoms with one oxygen atom give it a molar mass of 151.13 g/mol. The Hazardous Substances Data Bank (HSDB) reports that it forms needles or plates but is usually amorphous, with no ordered crystal structure. It does not melt in the ordinary way. Above 360 °C it decomposes, and part of it sublimes, passing straight from solid to vapour.

Structure and bonding

The viewer holds 16 atoms and 17 bonds in two fused rings, a hexagon and a pentagon sharing one carbon–carbon edge: the purine frame. With Labels on, the single O appears on the hexagon, double-bonded to its carbon. Next round the ring, past a nitrogen carrying one hydrogen, a carbon holds the amino nitrogen with its two hydrogens. Turned edge-on, the model lies flat: in PubChem’s computed conformer every atom sits within 0.002 Å of one plane. Space-filling turns the molecule into a thin, flat slab.

Ball-and-stick and Stick show each ring bond as fixed single or double. Hydrogen sits on two ring nitrogens: N1, beside the C=O, and N7 in the pentagon. That arrangement is the 1,7-dihydro form of the IUPAC name, and guanine has others. HSDB reports several desmotropic forms, versions of guanine that differ in where hydrogen atoms sit. The US Environmental Protection Agency (EPA) lists a 1,9-dihydro form in its chemical inventory.

The model shows guanine on its own. In DNA each guanine is part of a nucleotide, bonded to a sugar that also carries a phosphate group, and neither of those is drawn here.

Where it turns up

Haz-Map, a US occupational health database citing the Merck Index, describes guanine as a component of nucleic acids found throughout nature. ChEBI lists it as a human metabolite, a substance made or used in the body’s chemistry. It also records it as a metabolite of mice, of the yeast Saccharomyces cerevisiae, of Escherichia coli and of algae. The LOTUS natural-products database records it in Glycine max and in Fritillaria thunbergii, among other organisms.

It also occurs as a mineral. The RRUFF Project, a database of mineral data, lists a mineral named guanine, with the formula C₅H₃(NH₂)N₄O, under the International Mineralogical Association (IMA) number IMA1973-056.

In animal studies reported by HSDB, rats given guanine by mouth passed more of two nitrogen compounds, urea and ammonia, in their urine. On the laboratory side, chemists published preparations of guanine in 1897 and 1900, and in 1944 a version labelled with the isotope nitrogen-15, HSDB records.

Why it matters

In the double helix, a guanine on one strand faces a cytosine on the other, so every G is matched by a C across the strands, in NHGRI’s account. In Chem1’s account, hydrogen bonds link a nitrogen of one nucleotide to a nitrogen or oxygen opposite. Only the A–T and C–G pairs can hydrogen-bond efficiently in that arrangement, so those two pairs make up the alphabet that carries genetic information. G–C pairs also bind more tightly than A–T pairs, NHGRI notes, so long runs of G and C give a stronger helix than runs of A and T.

Outside the cell, guanine is a colour additive. HSDB reports that it is permanently listed under the US Federal Food, Drug, and Cosmetic Act for externally applied drugs and cosmetics, including those used around the eye. NORMAN, a network of environmental laboratories, classes it as a cosmetic colourant and opacifier, an ingredient that makes a product less see-through. The Consumer Product Information Database names 23 personal-care products containing it, and HSDB lists biochemical research among its uses.

Properties

Properties of guanine Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 135398634.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₅H₅N₅O
Molar mass	151.129(17) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	5
Hydrogen atoms	5
Nitrogen atoms	5
Oxygen atoms	1
Bonds	17
Single bonds	13
Double bonds	4
PubChem molecular weight	151.13 g/mol	g/mol	PubChem

Safety

Pure guanine powder is an irritant. Company notifications to the European Chemicals Agency (ECHA) classify it with the signal word Warning, as causing skin irritation and serious eye irritation and possibly irritating the airways. The PubChem Laboratory Chemical Safety Summary for guanine gives the full hazard information for anyone handling the solid.

Questions

What does the 3D model of guanine show?

It shows two rings fused along one edge, a six-membered ring and a five-membered ring, holding 16 atoms and 17 bonds. In PubChem's computed model every atom lies in a single plane. A double-bonded oxygen and an amino group, NH₂, hang from the larger ring. Only one hydrogen arrangement is drawn, while HSDB reports several desmotropic forms of guanine, differing in where hydrogen atoms sit.

What does guanine pair with in DNA?

Guanine pairs with cytosine. A guanine on one strand of the double helix faces a cytosine on the other, and hydrogen bonds hold the two together, according to the NHGRI glossary. In Chem1's description, the paired bases sit inside the helix, facing each other, while the sugar and phosphate backbones run along the outside.

Does guanine dissolve in water?

Barely. HSDB calls it almost insoluble in water, yet it dissolves freely in dilute acids and in aqueous potassium hydroxide, a strong base. Guanine combines with many acids, bases and metals, and HSDB records it on sale as a hydrochloride or a hemisulfate salt. The white solid is stable at room temperature, and on heating it decomposes rather than boiling.

Is guanine in RNA as well as DNA?

Yes. In the NHGRI glossary, RNA uses adenine, cytosine and guanine just as DNA does, with uracil taking the place of thymine. In both, guanine is carried inside a nucleotide, the building block of nucleic acids: a sugar bonded both to a phosphate group and to a base containing nitrogen. The sugar is ribose in RNA and deoxyribose in DNA, and in a written DNA sequence the letter G stands for guanine.

Made of the same elements

C₄H₅N₃O Cytosine 13 atoms, 13 bonds.
C₅H₄N₄O₃ Uric acid 16 atoms, 17 bonds.
C₅H₆N₂O₂ Thymine 15 atoms, 15 bonds.
C₄H₄N₂O₂ Uracil 12 atoms, 12 bonds.
C₂H₅NO₂ Glycine 10 atoms, 9 bonds.
CO(NH₂)₂ Urea 8 atoms, 7 bonds.
C₃H₇NO₂ Alanine 13 atoms, 12 bonds.
C₈H₁₀N₄O₂ Caffeine 24 atoms, 25 bonds.

All 25 compounds made of carbon, hydrogen, nitrogen and oxygen

C₅H₉NO₄ Glutamic acid 19 atoms, 18 bonds.
C₈H₉NO₂ Acetaminophen 20 atoms, 20 bonds.
C₈H₁₁NO₂ Dopamine 22 atoms, 22 bonds.
C₆H₁₃NO₂ Isoleucine 22 atoms, 21 bonds.
C₆H₁₃NO₂ Leucine 22 atoms, 21 bonds.
C₉H₁₁NO₂ Phenylalanine 23 atoms, 23 bonds.
C₁₀H₁₂N₂O Serotonin 25 atoms, 26 bonds.
C₉H₁₁NO₃ Tyrosine 24 atoms, 24 bonds.
C₁₁H₁₂N₂O₂ Tryptophan 27 atoms, 28 bonds.
C₉H₁₃NO₃ Epinephrine 26 atoms, 26 bonds.
C₁₂H₁₇NO DEET 31 atoms, 31 bonds.
C₁₃H₁₆N₂O₂ Melatonin 33 atoms, 34 bonds.
C₁₄H₁₈N₂O₅ Aspartame 39 atoms, 39 bonds.
C₁₄H₂₂N₂O Lidocaine 39 atoms, 39 bonds.
C₁₃H₂₁NO₃ Albuterol 38 atoms, 38 bonds.
C₁₇H₂₁NO Diphenhydramine 40 atoms, 41 bonds.
C₂₀H₂₄N₂O₂ Quinine 48 atoms, 51 bonds.