Mitochondrial DNA (mtDNA)

Mitochondrial DNA (mtDNA) is the small, circular genome inside your mitochondria. It is about 16,569 base pairs, present in many copies per cell. It encodes 13 essential parts of the energy-making complexes, plus 22 transfer RNAs and 2 ribosomal RNAs needed to build them on-site. It is more fragile than your nuclear DNA, for three reasons. It is packaged without protective histones. It sits right next to the electron transport chain, a major source of ROS. And it relies on a smaller, less-redundant set of repair enzymes. So mtDNA picks up mutations and deletions with age, especially in non-dividing tissues like muscle and brain. What does that do? It ranges from contributing to mitochondrial dysfunction (once mutated copies cross a threshold, called heteroplasmy) to triggering the cGAS-STING immune alarm (when mtDNA leaks into the cell during stress).

Last reviewed: June 22, 2026

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