14 February 2011

Mitochondria Are Real

I first became interested in mitochondria because of Charles Wallace Murry. He is an exceptionally smart 6-year-old—a child genius. He is extremely sick, dying of a progressive disease that leaves him weak and short of breath. Specifically, his mitochondria are sick.

And he is entirely made up.

Charles Wallace is the creation of Madeleine L’Engle. His disease is the main topic of her book The Wind in the Door. The story goes off with his sister on an outrageous escapade to save him. It is wild and over the top and unbelievable. I thought it was entirely fantasy.

But mitochondria are real.

It is difficult to believe that L’Engle didn’t make up mitochondria as well. There are hundreds to thousands of mitochondria in every living cell in your body. They have their own DNA, separate from your DNA. They replicate independently.

Mitochondria are membrane-bound organelles and have a double membrane, just like the nucleus of your cells, where your DNA is housed and replicated. However, the inner membrane of the mitochondria is heavily folded, greatly increasing the surface area of the membrane, and this is where sugars from food you eat is combined with oxygen to form ATP, the energy molecules used by your cells to move, contract, divide.

You probably got most of your mitochondria from your mother. There is some evidence that small amounts of mitochondria could get into the fertilized egg through the sperm, but generally speaking they are maternally inherited. So much so, in fact, that geneticists have traced entire lines of mitochondria back to 7 original ancestors, called the 7 Daughters of Eve. Sometime far back in evolution, an ancestor mitochondria became engulfed by a eukaryotic cell (like your cells) and an evolutionary cascade began that eventually resulted in humans.

There are hundreds or thousands of mitochondria in each of your living cells. Mitochondria produce all of the energy you use in your body. Without your mitochondria, you’d be in a pickle.

That’s why mitochondrial diseases are bad news.

Mitochondrial diseases like Charles Wallace’s may be caused by mutations in the mitochondrial DNA, or they could be inherited in the mitochondrial DNA. Mitochondria may also dysfunction due to drugs or infections. However, mitochondrial diseases are not very common. Maybe 1 in 1,000 children born each year in the US develops a mitochondrial disease. Anything going wrong with mitochondria usually results in an energy shortage, which most heavily affects tissues that are big energy consumers—muscle and brain tissue—resulting in effects such as dementia and muscle weakness, although there is a wide variety of possible effects throughout different organs.

Basically, each of your living cells contains hundreds or thousands of double-membraned organelles that have their own DNA and turn your food into energy. Can you blame me for thinking that was science fiction?

Unfortunately, the cure Charles Wallace’s sister Meg and her companions eventually find for his mitochondria’s sickness is fiction. There is no cure for mitochondrial diseases.