The Co-Evolution of Mitochondria

The attached article is a brief history of mitochondria –– the “energy factories” that we have in each cell (except mature red blood cells). Oncwe upon a time, more than a billion years ago, (either a random event? or divine intervention? resulted in) the swallowing-up of a small bacterium by a larger archaebacterium, more than a billion years ago, which resulted, not in death, but in one of the most successful partnerships on Earth. As you sit there, each of your cells (apart from your red blood cells) contains hundreds or thousands of the descendants of that bacterium –– still earning their keep as part of that endosymbiotic deal struck in some ancient tidal pool. However, a billion years of intimacy has blurred the distinction between these partners and shaped them irrevocably.

The host cell provides protection and food to mitochondria, and supplies all but a handful of the hundreds of proteins needed to run its affairs (this handful is encoded by a tiny rudimentary mitochondrial genome (mtDNA), a mere vestige of its bacterial forebear). The deal cuts both ways, though: because as a quid pro quo, the cell delegates a number of rather grubby tasks to these tiny organelles. The most obvious of these is that mitochondria make most of the cell’s energy currency, in the form of ATP. But they also help store and regulate calcium, synthesize and degrade specific chemicals, and take part in the cell’s decision to commit suicide (“programmed cell death”).

Like many factories, mitochondria are dangerous places with unpleasant chemicals, and handling the cell’s dirty work takes its toll on these organelles, threatening their integrity and that of their pared-down genomes. This makes the quality control of mitochondria in the face f such damage a crucial issue in evolution, disease, and aging. Therefore, after more than one billion years of living together, we have subjugated a free-living bacterium, turning it into a domesticated organelle. Humans would not nearly be the same –– without them..!!


PLoS Biol March 2o17; 15: e2002338

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