Drug or radiation effects on DNA that interfere with normal function, including conformational distortions and covalent gene mutations.

Drug-, radiation-induced, or spontaneous injuries to DNA that introduce deviations from its normal double-helical conformation. These changes include structural distortions that interfere with replication and transcription, as well as point mutations that disrupt base pairs and exert damaging effects on future generations through changes in DNA sequence. If the damage is minor, it can often be repaired (DNA repair); extensive damage can induce apoptosis.

Injuries to DNA that introduce deviations from its normal, intact structure and which may, if left unrepaired, result in a MUTATION or a block of DNA REPLICATION. These deviations may be caused by physical or chemical agents and occur by natural or unnatural, introduced circumstances. They include the introduction of illegitimate bases during replication or by deamination or other modification of bases; the loss of a base from the DNA backbone leaving an abasic site; single-strand breaks; double strand breaks; and intrastrand (PYRIMIDINE DIMERS) or interstrand crosslinking. Damage can often be repaired (DNA REPAIR). If the damage is extensive, it can induce APOPTOSIS.