what happens if change is unrepaired

Deamination is the removal of an amine group from a molecule. Enzymes that catalyse this reaction are called deaminases. Spontaneous deamination is the hydrolysis reaction of cytosine into uracil, releasing ammonia in the process.In DNA, this spontaneous deamination is corrected for by the removal of uracil (product of cytosine deamination and not part of DNA) by uracil-DNA glycosylase, generating an abasic (AP) site. The resulting abasic site is then recognised by enzymes (AP endonucleases) that break a phosphodiester bond in the DNA, permitting the repair of the resulting lesion by replacement with another cytosine.Spontaneous deamination of 5-methylcytosine results in thymine and ammonia. This is the most common single nucleotide mutation.