Most of us learned back in grade school that mitochondria are the power plants of our cells. These tiny organelles, some as small as half a micrometer, give our cells the energy needed to carry out basic functions. Our teachers probably spent just as much time covering mitochondria as they did covering the endoplasmic reticulum (our cell’s factory) and the Golgi apparatus (our cell’s FedEx). But forget those things. The fact that our school’s never offered a full semester-long course covering just the mitochondria is an insult to the field of biology. After all, these tiny intercellular generators are responsible for an enormous portion of our current understanding of taxonomy and biodiversity, play a major role in conservation and species management, and paved the way for the evolution of complex life on earth.
Much of our current taxonomic system relies heavily on the use and analysis of mitochondrial DNA (mtDNA). Since most sexually-reproducing organisms inherit their mitochondria maternally, it’s much easier to get a clear understanding of matrilineal phylogenies by examining the DNA sequence of mitochondrial genes. MtDNA is also highly conserved, exhibits relatively slow mutation rates, and degrades slowly compared to some forms of nuclear DNA (nDNA). Thus, researchers are able to utilize mtDNA to reconstruct ancient phylogenies and understand interspecies and intraspecies evolutionary relationships. If mitochondrial DNA did not exist, taxonomists (and scientists in general) would be working with a much poorer understanding of evolutionary relationships. We would also very likely be drastically underestimating global biodiversity. Since effective management of both endangered and invasive species relies heavily on an accurate understanding of these species’ or populations’ reproductive barriers, genetic diversity, and effective population sizes, we would be improperly managing both species that need our protection and species that need to be controlled. Without mtDNA, taxonomists and evolutionary biologists would be trying to illuminate the underground caverns of biodiversity with just a few matches.
But let’s be honest; mtDNA is just sort of a nice side effective of the existence of mitochondria. No one can really argue that the sole benefit of these organelles is the information they give us regarding evolutionary relationships. No, the real benefit of mitochondria is their ability to produce large amounts of energy, in the form of ATP, for our cells. Without mitochondria, eukaryotic cells would rely heavily on anaerobic fermentation, rather than the aerobic respiration allowed by mitochondria, for energy production. This process is about 13 times more inefficient than aerobic respiration, meaning eukaryotes would not have the ability to replicate, repair, and translate DNA at the scale many currently do. Cellular functions would decline if not break down, metabolic processes would go off the rails, and life as we know it would essentially cease to exist. And if you think that’s hyperbole, consider the fact that many researchers believe the only reason life was able to make the leap from tiny, basic cells to the tapestry of diverse, complex multi-cellular organisms we have today is because of mitochondria. About 1.5 billion years ago, an ancient cell (possibly a type of Archaea) engulfed an ancient bacteria and gave rise to the very first eukaryote. This host cell provided a favorable environment for the bacteria to grow and reproduce, and in return these “mitochondria” provided the host cell with an enormous amount of cellular energy through aerobic respiration. This new form of energy production allowed early eukaryotes to grow and create the vast diversity of plants, animals, and fungi that exist today. Without mitochondria, life on this planet would exist only as tiny, simple cells incapable of complex functions or physical growth. No mitochondria, no humans, no corgi puppies, no shark week, no Neil deGrasse Tyson, no three-toed sloths, no Lin Manuel Miranda. Life without mitochondria, however you slice it, would be a dull and boring affair.
May 26, 2016