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Diagram of a mitchondrion. Graphic: <a href="http://en.wikipedia.org/wiki/File:Mitochondrion_mini.svg">Kelvinsong</a>, released to the public domain
Diagram of a mitchondrion. Graphic: Kelvinsong, released to the public domain

Natural Selections: Mitochondria

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Dr. Curt Stager and Martha Foley explore the role of mitocondria--components that burn food molecules and produce energy--in cells.

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Martha Foley: What are mitochondria and why are they so important?

Dr. Curt Stager: It's not really a household word you usually run across…

MF: No, but you hear it once in a while; you hear it in relation to free radicals or little "engines."

CS: It's a component of all of our cells; basically all animals, all plants. If you look at them under a microscope, they look like blobs or strings--usually the illustrations in a book make them look like a bean--and you can have dozens or even hundreds of them in every one of your cells. And in fact they actually have variable shapes; they're more like baggies, or something like that, and sometimes they divide or even criss-cross and fuse with each other.

But it's basically a little component of your cell that burns your food. When you eat a meal the food is broken down into molecules in your digestive tract, and then it soaks into your bloodstream and oozes out to all the cells in your body. Those food molecules are taken up and brought into the inside of the cell where those mitochondria are waiting. They soak them up and literally burn the food molecules up one by one with oxygen that came from your lungs--which is why you breathe.

MF: And it produces energy.

CS: And then, in our case, there are two options with what to do with the energy inside these mitochondria. You can store it in a battery kind of a form by taking the energy and sticking a molecular bond onto a chemical. In our case it's called ATP, and it's like a little battery cell that gets charged by literally an electric motor inside the mitochondria running on oxygen and food that can be stored for anything your cells need to do: pumping stuff, moving, growing, dividing or whatever. So it's like money in the bank for your cells.

The other option is, you can decouple those little molecular machines, those little electric rotors, almost like putting the clutch in in a car and having it spin without doing any other work, and that makes heat. So they're not just a power station for making battery power for our cells, they're also a heat generator.

MF: So we’re warm-blooded because of mitochondria?

CS: If we didn't have mitochondria we would not be warm-blooded, although other animals have it, too. Fish have mitochondria, too, but it's just that their mitochondria don't have that ability to decouple from making that chemical energy, and just spin and make heat energy.

MF: So, they're really tiny, and they're in all of our cells, and they're sort of the source of the cell's energy.

CS: They're pretty much where the great stuff is happening. I mean, we focus a lot on genetics and the nucleus where all the genes are, but the mitochondria are really interesting. In fact, they have their own genes, too--their own circular DNA strands that don't resemble the DNA in your nucleus very much.

MF: What do they resemble?

CS: They're actually just like bacteria, which is not surprising, considering we're pretty sure now they used to be bacteria that lived independently. Bacteria have circular DNA, too. They have a double cell wall, just like mitochondria do., and a lot of bacteria can burn up food molecules with the help of oxygen.

MF: So, are all mitochondria basically the same? Duplicates of each other from you to me?

CS: Actually, the quality you could say of the mitochondria seems to vary from person to person. We inherit them from our moms basically (which is a whole other story), but there are going to be genetic differences between people with how well their mitochondria work. So if you're the kind of person with tons of energy all the time, maybe you have a super-efficient, high-energy design of mitochondria in your cells. That's a field of medical research now; maybe certain forms of lethargy could be related to defective mitochondria.

MF: I want some of that good kind of mitochondria.

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