DNA DAMAGE DNA damage, due to environmental factors and normal metabolic processes inside the cell, occurs at a rate of 1,000 to 1,000,000 molecular lesions per cell per day. While this constitutes only 0.000165% of the human genome’s approximately 6 billion bases (3 billion base pairs), if left unrepaired can cause mutations in critical genes (such as tumor suppressor genes) can impede a cell’s ability to carry out its function and appreciably increase the likelihood of tumor formation and disease states such as cancer. The vast majority of DNA damage affects the primary structure of the double helix; that is, the bases themselves are chemically modified. These modifications can, in turn, disrupt the molecules’ regular helical structure by introducing non-native chemical bonds or bulky adducts that do not fit in the standard double helix. Unlike proteins and RNA, DNA usually lacks tertiary structure and therefore damage or disturbance does not occur at that level. DNA is, however,...
