World View: Life, Science, and the Ramblings of a Mad Man

Mitochondria, Real Midi-clorians

People who have seen Star Wars know what midi-clorians are: the microscopic life forms that exist in every cell and give Jedi and Sith the ability to use the "Force." They are, in a way, like our own mitochondria (the singular of mitochondria, by the way, is mitochondrion). This is how the real "Force" works:

Like the midi-clorians in Star Wars, mitochondria live in all multicellular and even some unicellular organisms. They also give us the ability to undergo cellular respiration. This gives us a major boost in power (well, energy, but I guess they're the same thing). Humans use ATP (adenosine triphosphate) as the main "energy currency." ATP stores energy in a form that most energy-requiring processes in the body are able to use: everything including growth, repair, reproduction, movement—anything you can think of that takes up energy probably uses ATP. When cells undergo anaerobic respiration (the making of ATP without access to oxygen) they are able to produce 2 ATP molecules per glucose molecule, compared to the 38 ATP molecules that they are able to produce when they can use their mitochondria and undergo aerobic respiration. This huge difference in energy production is the reason all multicellular organisms need mitochondria.

So, they're important, but what are they? Well, mitochondria are organelles (little "organs" inside each of our cells which perform specific functions; most, if not all organelles are bound by cellular membranes—phosopholipid bilayers). Mitochondria, unlike most other organelles, actually have two membranes. The external membrane is involved in breaking down adrenaline and several other processes. The inner membrane is the one responsible for the conversion of ADP to ATP. Mitochondria also have a plasmid, a small, circular chromosome with several genes. Plasmids were known to biologists, before the mitochondria, as bacterial gene carriers. If you've ever heard of mitochondrial DNA or mtDNA, that's what was being referred to. These genes all produce specific proteins that are needed by the mitochondria (for more info on transcription /translation—the processes of turning DNA into proteins—see my first article on DNA or check out the wikipedia articles on them). Embedded in the membranes are specific proteins which are involved in the production of ATP or in detoxification (mitochondria, on top of creating ATP from ADP and breaking down adrenaline, also turn toxins into less toxic materials).

If you think it's strange that mitochondria have their own cell membranes, their own chromosomes, their own ribosomes, etc., you're not the only one. When scientists realized this, they began to hypothesize that (many, many, many—estimated at 10,000,000,000 years ago) mitochondria were bacteria that were able to undergo aerobic respiration and that through a symbiotic relationship, became a part of other cells. Through natural selection, some of these evolved into the multicellular organisms we are so used to seeing and dealing with today. This is now known as the endosymbiotic theory.

Mitochondria are able to use energy to convert ADT (adenosine diphosphate—a lower energy molecule than ATP) into ATP by a series of membrane-bound proteins. They take NADH and FADH2 (high-energy molecules which are not very easily used by cells) and release the end hydrogen, using the hydrogen’s electron to create a proton gradient (a high concentration of protons (hydrogen atoms without their electron) in the inner membrane. Membrane pumps keep the proton gradient up, while ATP synthase (also known as the F0F1 particle) uses the gradient by allowing protons through and using the energy (like a dam uses the energy of "high concentrations" of water) to turn ADP into ATP. NAD and FADH are given off as byproducts, which are reused in the cell for Glycolysis (breaking of glucose into two pyruvic acid molecule).

Now you know much more about mitochondria than you ever wanted to know—and if I'm wrong in saying that, then leave me a message and I'll get back to you with more information, or look them up yourself. They're actually pretty cool little buggers. See you guys next week, and hope you enjoyed this little intro to how the real "Force" works.