Walsh & Hoyt: Mitochondrial Genetics

Mitochondria are the only cellular organelles, aside from the nucleus, containing DNA. The mtDNA is a 16,569 base pair circle of double-stranded DNA. The majority of the 67 or so mitochondrial proteins are encoded by the nuclear genome, translated on cytoplasmic ribosomes, and transported into mitochondria. Mitochondrial DNA encodes 13 mitochondrial proteins as well as the two ribosomal RNAs (rRNAs) and 22 transfer RNAs (tRNAs) required to translate these proteins. Oxidative phosphorylation is carried out by the four multiprotein complexes of the respiratory chain and adenosine triphosphate (ATP) synthetase (complex V). The mtDNA encodes seven subunits of complex I(NADH-ubiquinone reductase), one subunit of complex III (ubiquinol-cytochrome c reductase), three subunits of complex IV (cytochrome c oxidase), and two subunits of ATP synthetase. Because the protein subunits of complex II (succinate dehydrogenase-ubiquinone reductase) are encoded exclusively by the nuclear genome, complex II activity is not impaired by mutations of the mitochondrial genome.