Mitochondria originated millions of years ago, likely when a eukaryotic cell incorporated a bacterium. Thus, mitochondrial DNA strands are 200,000× smaller than those from a cell’s nucleus. Depending on cell type, thousands of mitochondria can reside within the walls of one human cell. The scientific community long has considered these organelles to be cellular “energy factories.” But their centrality to human health and disease only now has come to light. In a breakthrough study published in Cell (1), biologists collaborated…