Difference Between Adenine and Guanine

Main Difference – Adenine vs Guanine

Adenine and guanine are two types of nitrogenous bases in nucleic acids. DNA and RNA are the nucleic acids found inside the cell. Nucleic acids are made up of three major components: a pentose sugar, nitrogenous base, and a phosphate group. Five types of nitrogenous bases can be found in nucleic acids. They are adenine, guanine, cytosine, thymine and uracil. Both adenine and guanine are purines. Cytosine, thymine, and uracil are pyrimidines. The main difference between adenine and guanine is that adenine contains an amine group on C-6, and an additional double bond between N-1 and C-6 in its pyrimidine ring whereas guanine contains an amine group on C-2 and a carbonyl group on C-6 in its pyrimidine ring.  

This article explains, 

1. What is Adenine
– Definition, Structure, Characteristics
2. What is Guanine
– Definition, Structure, Characteristics
3. What is the difference between Adenine and Guanine

Difference Between Adenine and Guanine - Comparison Summary

What is Adenine

Adenine is one of the two purines found in nucleic acids. It is attached to the 1′ carbon of the pentose sugar, ribose in RNA and deoxyribose in DNA, in its ninth atom, which is a nitrogen, forming a glycosidic bond. The functional group present in adenine is an amine group. In DNA, the pyrimidine base, thymine forms a complementary base pair with adenine. In RNA, uracil, which is also a pyrimidine base, forms a complementary base pair with adenine. Usually, adenine forms two hydrogen bonds with its complementary nucleotide, either thymine or uracil. The complementary base pairing occurs via hydrogen bonding between the two nitrogenous bases, assisting the stability of the nucleic acid structure. Adenine is shown in figure 1.

Difference Between Adenine and Guanine

Figure 1: Adenine

Adenine is synthesized in the liver. It is derived from inosine monophosphate (IMP). The synthesis of adenine requires folic acid. Adenosine triphosphate (ATP) is the mostly occurring chemical energy sources, which energizes the cellular processes. ATP contains two high energy phosphates. The cofactors, nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD) along with ATP are involved in the cellular respiration as carriers of energy from one reaction to the other. 

What is Guanine

Guanine is the other purine, which occurs in nucleic acids. It is also attached to the 1’carbon of the two types of pentose sugars via a glycosidic bond. Two functional groups are present in Guanine: an amine group on C-2 and a carbonyl group on C-6. In both DNA and RNA, guanine complementary base pairs with the pyrimidine, cytosine. Three hydrogen bonds are formed between guanine and cytosine.

Difference Between Adenine and Guanine - 3

Figure 2: Guanine

Guanine is also synthesized via IMP during the de novo synthesis of purine bases. Like ATP, guanine serves as an energy source in protein synthesis as well as gluconeogenesis. GTP plays a vital role in signal transduction as a second messenger. Guanine tautomerization is the interchanging of guanine between the keto and enol functionality through intermolecular proton transfer. Guanine tautomerization is shown in figure 3.

Main Difference - Adenine vs Guanine

Figure 3: Guanine tautomerization

Difference Between Adenine and Guanine

Complementary Base Pairing

Adenine: Adenine forms complementary base pairs with thymine in DNA and uracil in RNA.

Guanine: Guanine forms complementary base pairs with cytosine in both DNA and RNA.

Functional Groups

Adenine: Adenine contains an amine group on C-6 in its pyrimidine ring.

Guanine: Guanine contains an amine group on C-2 and a carbonyl group on C-6 in its pyrimidine ring.  


Adenine: Molecular formula of adenine is C5H5N5 .

Guanine: Molecular formula of guanine is C5H5N5O.

Molecular Mass

Adenine: Molecular mass of adenine is 135.13 g/mol.

Guanine: Molecular mass of guanine is 151.13 g/mol.

Solubility in Water

Adenine: Solubility in water is 0.103 g/100 mL.

Guanine: Guanine is insoluble in water.

Other Functions

Adenine: ATP, NAD, and FAD serve as energy carriers.

Guanine: GTP serves as a second messenger.


Adenine and guanine are purines made up of two rings of nitrogen and carbon atoms. The two rings are formed by a six-membered pyrimidine ring fusing with a five-membered imidazole ring.   The two rings are fused together, forming a single, flat structure. Both adenine and guanine are formed from the same precursor, IMP. IMP is synthesized from sugars and amino acids in a series of steps in the de novo synthesis. Melting points of both adenine and guanine are the same, which is 360 °C. They differ from the functional groups, which are attached to the purine core of each molecule.

1. Fort, Ray. “Structure and properties of purines and pyrimidines.” Purines and Pyrimidines. N.p., n.d. Web. 14 May 2017. </
2. “Structural Biochemistry/Nucleic Acid/Nitrogenous Bases/Purines/Adenine.” Wikibooks, open books for an open world. N.p., n.d. Web. 14 May 2017. </
3. “Structural Biochemistry/Nucleic Acid/Nitrogenous Bases/Purines/Guanine.” Wikibooks, open books for an open world. N.p., n.d. Web. 14 May 2017. </

Image Courtesy:
1. “Adenine numbered” By Adeaminase – Own work via
2. “Guanine” by chronoxphya via
3. “Guanine” By Mrbean427 – guanine tautaumerization  via

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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