The above image is an individual mitochondria (click image to enlarge). Mitochondria are the cell's power plant, their energy source, and help regulate many cellular functions in our bodies, including individual cell death. Most every cell has fetaures inside which are designated "organelles," and which run various functions of the cell. Mitochondria are one of these organelles, but not your run-of-the-mill kind.
There are mitochondria in every single living cell of every single animal, plant, fungus, and protists (algae and lichens) in existence on the planet Earth today. It has been this way for over a BILLION years. In 1905 a Russian botanist, Konstantin Mereschkowski, postulated a theory that sounded so far-fetched, so bizarre, as to be almost unbelievable. His idea is that mitochondria are the end result of an invasion, billions of years ago, by one-celled organisms INTO other one-celled organisms. The mitochondria became symbiates, co-existing inside the original cells it invaded. This idea has come to be called Endosymbiotic Theory.
Research into this idea blew people's minds! It seems to be correct and explains some very strange features and characteristics of mitochondria. Here are a few.
- Mitochondria contain their own DNA, which is different from the DNA in the cell nucleus. Not only is it different DNA, but it is a different kind of DNA, smaller and circular (not the double-helix), which more strongly resembles the DNA found in modern-day bacteria.
- The Mitochondria are surrounded by 2 or more membranes, the interior one being very different from the membranes of the surrounding cell, more like the composition of membranes from cells lacking nuclei, which are the most primitive cells we know of.
- Much of the interior structure of Mitochondria closely resembles that of cyanobacteria, a very primitive form of life which exists in the harshest of environments, from deep ocean trenches of insane pressure, to underground hot zones inhospitable to any life. Cyanobacteria survive through chemical reactions, getting their energy from chemicals in their environments, as opposed to the photosynthesis of plants or the digestion of animals.
All in all, it is a fairly accepted view now among the biologists of the world that Mitochondria are ancient invaders. Because the Mitochondria itself has a different DNA genome than the cell's nucleus, scientists are now able to use mitochondrial DNA to trace back species and individual human lines. It is amazing shit. Are we all just vehicles for our Mitochondria? It would seem so.
Here is a simplified drawing of a Mitochondria's parts.