What are mitochondria?

Q: What are mitochondria? Is that where we get our energy?

Q: Are mitochondria present in all plants and animals? What is the current theory on how mitochondria evolved? Are they all the same?
Someone, Texas, USA

A: "Biology Department, UNM" a young woman answers the phone.

I ask to speak with an expert on mitochondria (my-toe-KON-dree-a). She pauses.

"What's mitochondria?" I hear her say to a friend.

Mitochondria are tiny sacs—so small you need an electron microscope to see them—elongated, like a sausage. Many bop around in each heart, pancreas, or kidney cell. Few live in a skin cell. All living cells, however, have mitochondria (except bacteria and cyanobacteria, formerly called blue-green algae).

Mitochondria power life. Their job is to burn food and produce power packets (called ATP molecules, whose initials stand for Adenosine Tri Phosphate).

The young woman comes back on the phone and refers me to Don Natvig, a molecular biologist and professor at the University of New Mexico. Unfortunately, he's in a tearing hurry, gives me quick answers, and promises more when I call back at 3.

Back I go to surfing the web. How did mitochondria evolve? A mouse click gives the answer.

Earth formed 4.5 billion years ago. Life began a billion years later as one-celled bacteria so primitive they had no nucleus. Bigger cells with nuclei evolved about 2 billion years after that.

Around then, or in another 700 million years, mitochondria developed. Current theory says a big cell engulfed a little one or a little one infected a big one.

The big cell refrained from digesting or destroying the little fellow. Both profited. The big guy gained extra power packets and the little guy found food and a stable home. The mutual symbiotic relationship persisted and now is so strong that each cannot survive without the other.

It is 3 o'clock and time to call Don, the molecular biologist. I ask my question: do mitochondria differ between plants and animals?

"Yeees," he draws out the answer. "But their function is the same in both. They make ATP (power packets). The difference is like that between a Chevy and a Ford." Not much.

He produces examples. "Plant and animal mitochondria have slightly different genes and differ a bit in how they process them."

Mitochondria have their own genes, separate from the genes inside each cell's nucleus. What's more, mitochondrial genes come only from the mother, not both parents. In fact, the FBI tracks maternal relatives using mitochondrial DNA.

Further Surfing:

On line biology, M. J. Farabee: How a cell is organized

(Answered Sep. 27, 2002; updated on Aug. 28, 2007)