Normal oxidative damage to mitochondrial and nuclear DNA is extensive.

TLDR

Oxidative DNA damage arises from reactive oxygen species generated by radiation or aerobic metabolism, and the oxidized base 8‑hydroxydeoxyguanosine (8‑OHdG) has been measured in rat liver DNA. High 8‑OHdG levels in mtDNA may result from intense oxygen metabolism, poor DNA repair, and lack of histones. 8‑OHdG occurs at 1 per 130,000 bases in nuclear DNA and 1 per 8,000 bases in mtDNA, rises with prooxidant treatment, and may explain mtDNA’s high mutation rate.

Abstract

Oxidative damage to DNA can be caused by excited oxygen species, which are produced by radiation or are by-products of aerobic metabolism. The oxidized base, 8-hydroxydeoxyguanosine (oh8dG), 1 of approximately 20 known radiation damage products, has been assayed in the DNA of rat liver. oh8dG is present at a level of 1 per 130,000 bases in nuclear DNA and 1 per 8000 bases in mtDNA. Mitochondria treated with various prooxidants have an increased level of oh8dG. The high level of oh8dG in mtDNA may be caused by the immense oxygen metabolism, relatively inefficient DNA repair, and the absence of histones in mitochondria. It may be responsible for the observed high mutation rate of mtDNA.