Frequency of DNA Damage
The frequency of a particular type of damage is the number of molecules of the damage (adduct) occurring in a defined amount of DNA. This is a measure of the damage and is highly correlated with the resulting genotoxicity.
As mentioned earlier, it is impossible to avoid all DNA damage. Even DNA samples from healthy individuals show significant levels of oxidized bases and other damage products. Many measurements have been done on levels of DNA damage under various settings with DNA from both humans and experimental animals. The question is often raised as to what level of DNA damage is a problem, particularly in regulatory settings. A precise answer cannot be given, in that the biological outcome is dependent not only on the frequency of DNA damage but also on (i) the chemical nature of the lesion, (ii) the site of the DNA base to which it is attached, (iii) the gene and position at which it is found, (iv) its rate of repair, and (v) phenomena such as the DNA...