Mitochondria are small rod-like structures, or organelles, located within cells. They serve as ‘power plants’ that produce the energy cells need to function, by processing fats and sugars from food and combining them with oxygen to create energy-storage molecules called adenosine triphosphate (ATP). This process is known as oxidative phosphorylation or cellular respiration. When needed, ATP is broken down to release this stored energy.

Mitochondria have their own supply of DNA (mtDNA) that is distinct from the normal DNA in the cell’s nucleus. As the mitochondria copy their DNA, errors are often made. As these dysfunctional mutations accumulate, the mitochondria become less able to generate energy efficiently.