Guanine is one of the five main
nucleobaseNucleobases are the parts of DNA and RNA that may be involved in pairing . The main ones are cytosine, guanine, adenine , thymine and uracil , abbreviated as C, G, A, T, and U, respectively. They are usually simply called bases in genetics...
s found in the
nucleic acidA nucleic acid is a macromolecule composed of chains of monomeric nucleotides. In biochemistry these molecules carry genetic information or form structures within cells. The most common nucleic acids are deoxyribonucleic acid and ribonucleic acid . Nucleic acids are universal in living things, as...
s
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
and
RNARibonucleic acid is a biologically important type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate...
, the others being
adenineAdenine is a nucleobase with a variety of roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate and the cofactors nicotinamide adenine dinucleotide and flavin adenine dinucleotide , and protein synthesis, as a chemical component of DNA...
,
cytosineCytosine is one of the four main bases found in DNA and RNA. It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...
,
thymineThymine is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine always pairs with adenine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. As the name suggests, thymine may be...
, and
uracilUracil is a common and naturally occurring pyrimidine derivative. Originally discovered in 1900, it was isolated by hydrolysis of yeast nuclein that was found in bovine thymus and spleen, herring sperm, and wheat germ...
. In
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
, guanine is paired with cytosine. With the formula C
5H
5N
5O, guanine is a derivative of
purineA purine is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. Purines, including substituted purines and their tautomers, are the most widely distributed kind of nitrogen-containing heterocycle in nature....
, consisting of a fused pyrimidine-imidazole ring system with conjugated double bonds. Being unsaturated, the bicyclic molecule is planar. The guanine
nucleosideNucleosides are glycosylamines consisting of a nucleobase bound to a ribose or deoxyribose sugar. Examples of these include cytidine, uridine, adenosine, guanosine, thymidine and inosine....
is called
guanosineGuanosine is a nucleoside comprising guanine attached to a ribose ring via a β-N
9-glycosidic bond.Guanosine can be phosphorylated to become GMP , cGMP , GDP and GTP .When guanine is attached to a deoxyribose ring, it is known as a...
.
Basic principles
Guanine, along with adenine and cytosine, is present in both DNA and RNA, whereas thymine is usually seen only in DNA, and uracil only in RNA. Guanine has two
tautomerTautomers are isomers of organic compounds that readily interconvert by a chemical reaction called tautomerization. It is common that this reaction results in the formal migration of a hydrogen atom or proton, accompanied by a switch of a single bond and adjacent double bond. In solutions in which...
ic forms,
the major keto form (see figures) and rare enol formIn organic chemistry, keto-enol tautomerism refers to a chemical equilibrium between a keto form and an enol. The enol and keto forms are said to be tautomers of each other...
.
It binds to cytosine through three
hydrogen bondA hydrogen bond is the attractive interaction of a hydrogen atom with an electronegative atom, like nitrogen, oxygen or fluorine . The hydrogen must be covalently bonded to another electronegative atom to create the bond...
s. In cytosine, the amino group acts as the hydrogen donor and the C-2 carbonyl and the N-3 amine as the hydrogen-bond acceptors. Guanine has a group at C-6 that acts as the hydrogen acceptor, while the group at N-1 and the amino group at C-2 act as the hydrogen donors.
The first isolation of guanine was reported in 1844 from the excreta of sea birds, known as guano, which was used as a source of fertilizer. About fifty years later, Fischer determined the structure and also showed that uric acid can be converted to guanine. Facial treatments using the droppings, or guano, from Japanese nightingales is currently in favor in New York, reportedly because the guanine in the droppings produces a clear, "bright" skin tone that some people find desirable to attain.
Guanine can be hydrolyzed with strong acid to
glycineGlycine is an organic compound with the formula NH2CH2COOH. With only a hydrogen atom as its side chain, glycine is the smallest of the 20 amino acids commonly found in proteins....
,
ammoniaAmmonia is a compound of nitrogen and hydrogen with the formula NH
3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers...
,
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
, and
carbon monoxideCarbon monoxide is a colorless, odorless and tasteless gas, yet very toxic to humans. It consists of one carbon atom and one oxygen atom, connected by a covalent double bond and a dative covalent bond...
. Guanine is first deaminated to
xanthineXanthine , , is a purine base found in most human body tissues and fluids and in other organisms. A number of mild stimulants are derived from xanthine, including caffeine and theobromine....
. Guanine oxidizes more readily than adenine, the other purine-derivative base in DNA. Its high melting point of 350°C reflects the intermolecular hydrogen bonding between the oxo and amino groups in the molecules in the crystal. Because of this intermolecular bonding, guanine is relatively insoluble in water, but it is soluble in dilute acids and bases.
Syntheses
Trace amounts of guanine form by the polymerization of ammonium cyanide (NH
4CN). Two experiments conducted by Levy et al. showed that heating 10 mol·L
−1 NH
4CN at 80 °C for 24 hours gave a yield of 0.0007%, while using 0.1 mol·L
−1 NH
4CN frozen at -20 °C for 25 years gave a 0.0035% yield. These results indicate guanine could arise in frozen regions of the primitive earth. In 1984, Yuasa reported a 0.00017% yield of guanine after the electrical discharge of NH
3, CH
4, C
2H
6, and 50 mL of water, followed by a subsequent acid hydrolysis. However, it is unknown whether the presence of guanine was not simply a resultant contaminant of the reaction.
- 5NH3 + CH4 + 2C2H6 + H2O → C5H8N5O (guanine) + (25/2)H2
A Fischer-Tropsch synthesis can also be used to form guanine, along with adenine, uracil, and thymine. Heating an equimolar gas mixture of CO, H
2, and NH
3 to 700 °C for 15 to 24 minutes, followed by quick cooling and then sustainted reheating to 100 to 200 °C for 16 to 44 hours with an alumina catalyst, yielded guanine and uracil:
- 5CO + (1/2)H2 + 5NH3 → C5H8N5O (guanine) + 4H2O
Another possible abiotic route was explored by quenching a 90% N
2–10%CO–H
2O gas mixture high-temperature plasma
Traube's synthesis involves heating 2,4,5-triamino-1,6-dihydro-6-oxypyrimidine (as the sulfate) with formic acid for several hours.
Other uses
In 1656 in Paris, François Jaquin (a rosary maker) extracted from scales of some fishes the so-called pearl essence, crystalline guanine forming
G-quadruplexNucleic acid sequences which are rich in guanine are capable of forming four-stranded structures called G-quadruplexes . These consist of a square arrangement of guanines , stabilized by Hoogsteen hydrogen bonding. They are further stabilized by the existence of a monovalent cation in the center...
es. In the cosmetics industry, crystalline guanine is used as an additive to various products (e.g.,
shampooShampoo is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and other contaminant particles that gradually build up in hair...
s), where it provides a pearly
iridescentIridescence is generally known as the property of certain surfaces which appear to change colour as the angle of view changes. Iridescence may be seen commonly in soap bubbles, butterfly wings and sea shells.- Description :...
effect. It is also used in metallic paints and simulated pearls and plastics. It provides shimmering luster to eye shadow and
nail polishNail polish is a lacquer applied to toenails or fingernails for appearance, but also as nail protection. Polishing afterward without adding another chemical layer is called nail buffing.-History:...
. Guanine crystals are rhombic platelets composed of multiple transparent layers, but they have a high index of refraction that partially reflects and transmits light from layer to layer, thus producing a pearly luster. It can be applied by spray, painting, or dipping. It may irritate the eyes. Its alternatives are
micaThe mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic with a tendency towards pseudo-hexagonal crystals and are similar in chemical composition...
, faux pearl (from ground shells), and
aluminiumAluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances....
and
bronzeBronze is a metal alloy consisting primarily of copper, usually with tin as the main additive, but sometimes with other elements such as phosphorus, manganese, aluminium, or silicon. It was particularly significant in antiquity, giving its name to the Bronze Age...
particles.
The spiders and scorpions convert ammonia, as a product of protein metabolism in the cells, to guanine as it can be excreted with minimal water loss.
In nature, the
OarfishOarfish are large, greatly elongated, pelagic Lampriform comprising the small family Regalecidae. Found in all temperate to tropical oceans yet rarely seen, the oarfish family contains four species in two genera...
is covered with skin made of guanine.
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