The deoxyribose in its sugar–phosphate backbone makes chains of DNA chemically much more stable than chains of RNA, so that DNA can grow to greater lengths without breakage.

The other differences between RNA and DNA—the double-helical structure of DNA and the use of thymine rather than uracil—further enhance DNA stability by making the molecule easier to repair.

A damaged nucleotide on one strand of the double helix can be repaired by using the other strand as a template. Furthermore, deamination, one of the most common detrimental chemical changes occurring in polynucleotides, is easier to detect and repair in DNA than in RN

This is because the product of the deamination of cytosine is, by chance, uracil, which already exists in RNA, so that such damage would be impossible for repair enzymes to detect in an RNA molecule. However, in DNA, which has thymine rather than uracil, any uracil produced by the accidental deamination of cytosine is easily detected and repaired.