Editing Mutagen (section)

==Difference between mutagens and DNA damaging agents==

A [[DNA damage (naturally occurring)|DNA damaging agent]] is an agent that causes a change in the structure of DNA that is not itself replicated when the [[DNA replication|DNA is replicated]].<ref name = Bernstein1991>Bernstein, C.; Bernstein, H. (1991). Aging, Sex, and DNA Repair. pgs. 15-16. San Diego: Academic Press. {{ISBN|978-0-12-092860-6}}</ref>  Examples of DNA damage include a chemical addition or disruption of a [[nucleotide]] base in DNA (generating an abnormal nucleotide or nucleotide fragment), or a break in one or both strands in DNA.  When duplex DNA containing a damaged base is replicated, an incorrect base may be inserted in the newly synthesized strand opposite the damaged base in the complementary template strand, and this can become a [[mutation]] in the next round of replication.  Also a DNA double-strand break may be repaired by an inaccurate process leading to an altered base pair, a mutation.  However, mutations and DNA damages differ in a fundamental way: mutations can, in principle, be replicated when DNA replicates, whereas DNA damages are not necessarily replicated.  Thus DNA damaging agents often cause mutations as a secondary consequence, but not all DNA damages lead to mutation and not all mutations arise from a DNA damage.<ref name = Bernstein1991/>  The term genotoxic means toxic (damaging) to DNA.