This transmission electron microscope image reveals mitochondria in a thin section of mammalian lung tissue.
Image courtesy of the Dartmouth Electron Microscope Facility Dartmouth College
Just as a car's combustion engine converts gasoline into motion, tiny engines nestled inside your cells are converting food and oxygen into a form of energy that your body can use. These cellular powerhouses are known as mitochondria (the singular is "mitochondrion"). They are found in most plant and animal cells, but not in bacteria.
Mitochondria are very efficient energy producers in the presence of oxygen. Although cells have other means of producing energy if oxygen is unavailable, no other process is as efficient as the mitochondrion's method.
Mitochondria are made up of over 1,000 proteins, but only about a dozen of these are encoded in the single, circular piece of DNA that resides in the mitochondria (known as mitochondrial DNA or mtDNA for short). The rest of the proteins that make up the mitochondria are actually encoded in the nuclear genome - the genetic material that sits inside the cell's nucleus.
Mitochondrial DNA is passed from parent to child in a rather unique way. In humans, 23 chromosomes reside in the cellular nucleus. During reproduction both parents pass along genetic information encoded in these chromosomes to an offspring. But the single circle of mitochondrial DNA tends to come from the mother only. This means that the mitochondrial genome undergoes less genetic shuffling, allowing researchers to trace an individual's ancestry through the maternal line using mitochondrial DNA.
It might surprise you to know that mitochondrial DNA has much in common with bacterial DNA, in terms of its overall size and structure. This may be because mitochondria are the descendents of an ancient, free-living bacterium. Scientists hypothesize that billions of years ago, a cell engulfed one of these tiny organisms. Instead of being digested and destroyed, the way most foreign bodies are, it survived and received food and nourishment from its host cell. And in return, the host received energy. This mutually beneficial relationship gave rise to modern mitochondria.
Because of the critical role that mitochondria play in breaking down nutrients and efficiently converting these raw materials into energy packets, any flaws in the mitochondria can have a serious impact on human health. A range of diseases - including neurological disorders, diabetes, Parkinson's, and many others - may be tied to defects in the mitochondrion.
Want to learn more?
You can find out how Broad scientists and collaborators developed a catalog of all of the proteins that make up mitochondria by reading the news story, "Parts list for a powerhouse." Broad scientists involved in the Metabolism Program are studying the mitochondria to find genes that underlie rare inherited syndromes or may be tied to common diseases like diabetes. To find out more about the interplay between the nuclear genome and mitochondria, you can check out the news story, "A deep look into the mitochondrial ‘proteome.'"