Guanine

Guanine is a purine nucleobase in DNA and RNA that pairs with cytosine through three hydrogen bonds. Its chemical formula is C₅H₅N₅O.

Purine: A nitrogen-containing two-ring structure that forms the core of adenine and guanine. Guanine belongs to this structural family, which distinguishes it from single-ring pyrimidine bases.
Watson–Crick base pairing: The specific hydrogen-bond pairing of adenine with thymine or uracil and guanine with cytosine. Guanine's standard partner and three hydrogen bonds exemplify this pairing scheme.
Guanine nucleotide: A nucleotide containing guanine, ribose or deoxyribose, and phosphate groups. These compounds supply guanine units for nucleic-acid synthesis and cellular reactions.
Adenine: A purine nucleobase that pairs with thymine in DNA and uracil in RNA. Adenine shares guanine's two-ring scaffold but has a different partner and hydrogen-bond pattern.
Nucleobase: A nitrogen-containing molecule that forms part of nucleotides in DNA and RNA. Guanine is one of the bases that encodes information in nucleic acids.
Hydrogen bond: An attractive interaction involving a hydrogen atom bonded to an electronegative atom and another electronegative atom. Three hydrogen bonds connect guanine to cytosine in canonical base pairs.
Guanosine triphosphate: A guanine nucleotide with three phosphate groups that powers cellular processes and signaling. Guanine's ribose-containing nucleotide form becomes a widely used cellular energy and signaling molecule.
Thymine: A pyrimidine nucleobase used in DNA that pairs with adenine. Thymine illustrates the contrasting DNA pair rather than guanine's cytosine pair.
Cytosine: A pyrimidine nucleobase in DNA and RNA that pairs with guanine. Its complementary pairing with guanine helps maintain accurate nucleic-acid structure.
Guanine tautomerism: The interconversion of guanine forms that differ in the placement of hydrogen atoms and double bonds. Rare guanine tautomers can alter its pairing behavior and contribute to replication errors.

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