Definition of Mitochondrion

Mitochondrion: Singular of mitochondria. The mitochondria are normal structures called organelles in cells. They are located in the cell's cytoplasm outside the nucleus.

The mitochondria are responsible for energy production. They consist of two sets of membranes, a smooth continuous outer coat and an inner membrane arranged in tubules or in folds that form plate- like double membranes (cristae). The mitochondria are in fact the principal energy source of the cell (thanks to the cytochrome enzymes of terminal electron transport and the enzymes of the citric acid cycle, fatty acid oxidation, and oxidative phosphorylation). The mitochondria convert nutrients into energy as well as doing many other specialized tasks.

Each mitochondrion has a chromosome that is made of DNA but is otherwise quite different from the better known chromosomes in the nucleus. The mitochondrial chromosome is much smaller. It is round (whereas the chromosomes in the nucleus are shaped like rods). And there are many copies of the mitochondrial chromosome in every cell (whereas there is normally only one set of chromosomes in the nucleus).

No matter whether we are male or female, we inherit our mitochondrial chromosome from our mother. In other words, the mitochondrial chromosome is transmitted in a matrilinear manner. We have Eve to thank for our mitochondrial chromosome.