Editing Mutagenesis (section)

=== Spontaneous hydrolysis ===
DNA is not entirely stable in aqueous solution, and [[depurination]] of the DNA can occur. Under physiological conditions the [[glycosidic bond]] may be hydrolyzed spontaneously and 10,000 [[purine]] sites in DNA are estimated to be depurinated each day in a cell.<ref name="loeb">{{Cite journal 
| last1 = Loeb | first1 = L. A. 
| title = Endogenous carcinogenesis: Molecular oncology into the twenty-first century--presidential address 
| journal = Cancer Research 
| url = http://cancerres.aacrjournals.org/content/49/20/5489.full.pdf
| volume = 49 
| issue = 20 
| pages = 5489–5496 
| year = 1989 
| pmid = 2676144
}}</ref> Numerous DNA repair pathways exist for DNA; however, if the apurinic site is not repaired, misincorporation of nucleotides may occur during replication. Adenine is preferentially incorporated by DNA polymerases in an [[apurinic site]].

Cytidine may also become [[Deamination|deaminated]] to uridine at one five-hundredth of the rate of depurination and can result in G to A transition. Eukaryotic cells also contain [[5-methylcytosine]], thought to be involved in the control of gene transcription, which can become deaminated into thymine.