**3.5 DNA strand breaks**

 These injuries are divided based on the breaking of one or both strands. Single strand breaks (SSBs) can be generated by normal cellular procedures that went wrong, such as erroneous or abortive activity of DNA topoisomerase I (Top1), which presents mitochondrial localization, and when it fails may produce proteinlinked DNA breaks [23], also SSBs are produced by ineffective base excision repair (BER), or by oxidative stress [24]. One lesion related to SSBs is the formation of a covalently linked AMP to a 5′ phosphate, product of an unsuccessful DNA ligase activity [25]. On the other hand, double strand breaks (DSBs) are the most harmful, since they can provoke global cellular responses that involve many aspects of cell metabolism [26]. These lesions may occur by endogenous agents like reactive oxygen species (ROS), errors in DNA metabolism by topoisomerases, and nucleases or detention of replisome. On the other hand, lesion can be caused by exogenous insults such as ionizing radiation and chemotherapeutic drugs [1].
