Mitochondrial Genomics and Targeted Toxicities

Mitochondria are essential subcellular organelles, generating >90% of the cellular ATP needed to meet the functional needs of the organism. Mitochondria harbor an essential, high copy number, 16,569 base pair, circular DNA genome that encodes 13 gene products required for well-coupled electron transport and oxidative phosphorylation. Damage to this genome, either from environmental exposures, heritable mutations, or endogenous oxidative stress, can compromise cellular respiration, and give rise to mitochondrial toxicity and mitochondrial disease. In this article we review the structure and composition of the mitochondrial genome in the context of susceptibility to exposure-related mtDNA damage along with processes that maintain the integrity and stability of mtGenome. We then describe examples of exposures that cause genotoxic damage and mutations in mtDNA. The mechanism of mtDNA replication is reviewed as the origins of mitochondrial mutagenesis. The primary pathways of mtDNA repair are also described which, together with the high degree of genetic redundancy, accounts for thresholds of exposure-related mitochondrial toxicities, bioenergetic deficits, and metabolic disease.