nucleobases

Nucleobases are nitrogen-containing heterocyclic aromatic molecules that encode genetic information in nucleic acids. The five canonical bases used in biology are the purines adenine and guanine, and the pyrimidines cytosine, thymine, and uracil. Thymine is characteristic of DNA, whereas uracil is found in RNA in place of thymine.

Across DNA and RNA, bases form specific hydrogen-bonded pairs: adenine pairs with thymine in DNA (two hydrogen bonds) or with uracil in RNA, and guanine pairs with cytosine (three hydrogen bonds). These pairings, along with base-stacking interactions, stabilize the double helix and govern the structure of RNA folds.

A nucleobase is linked to a sugar to form a nucleoside; attachment to deoxyribose yields a deoxynucleoside, and attachment to ribose yields a ribonucleoside. Phosphates attached to the sugar produce nucleotides, the monomers of DNA and RNA.

Nucleobases are produced by cellular metabolism through de novo synthesis and salvage pathways. In DNA and RNA, many bases also occur as modified forms with roles in regulation and stability, such as 5-methylcytosine in DNA and pseudouridine in RNA.

Chemical tautomers of bases can lead to mispairing and mutations; deamination and other processes can alter bases if not repaired, affecting genetic information. The distinct properties of the bases, including hydrogen-bonding patterns and methylation status, underpin genetic coding, replication fidelity, and gene regulation.