Reactive oxygen species
The metabolism that occurs in every cell and is associated with the basic requirements of physiology inevitably leads to the production of reactive intermediates, many of which are capable of reacting with DNA or free dNTPs, which could subsequently be incorporated during synthesis. One particular group of such molecules are called reactive oxygen species (ROS). The essential feature of ROS is the presence of an unpaired electron on an oxygen atom in the molecule, which enables the ROS to react with DNA and lead to either strand breakage or the generation of modified bases such as 8-oxoguanine. The occurrence of a strand break is potentially lethal to a cell. Specific DNA repair pathways exist to remove 8-oxoguanosine triphosphate from the cellular dNTP pool and to remove 8-oxoguanine bases from DNA strands.