Mitochondria: unravelling the secrets of life and death

Abstract

The endosymbiont theory states that 1.5 billion years ago a primitive anaerobic cell ingested a neighbouring bacterium. A successful alliance was to develop that would dramatically change the nature of life on this planet. The ingested prey was no ordinary bacterium. It was able to respire, utilising the oxygen that was becoming more abundant in the earth's atmosphere to oxidise its food. The host cell was able to utilise the large amounts of energy produced during respiration to develop more complex regulatory mechanisms, eventually becoming the eukaryotic cell from which all multicellular plants and animals evolved. The aerobic bacterium and its descendants were destined to become mitochondria, the combustion engines of the eukaryotic cell. But these organelles are not just the life force of the cell; they are also its executioners. Mitochondria appear to sense a variety of cellular signals and stresses, and orchestrate the release of factors that trigger the host's suicide pathways. In June and July, two papers have appeared in the journal Nature that investigate these life and death pathways of mitochondria.^1,2 They provide an opportunity to outline and compare the status of these two fundamental aspects of mitochondrial research.