Mitochondria

The mitochondria are normal energy- producing structures within 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.

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Plural of mitochondrion.

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mi·to·chon·dria (mi″to-konґdre-ə) sing. mitochonґdrion [mito- + chondri- + -ia] small spherical to rod-shaped cytoplasmic organelles, consisting of inner and outer bilayer membranes with a space between them. The inner membrane is infolded to form a series of projections (cristae), and the space between the cristae is filled by the mitochondrial matrix, which contains DNA, RNA, ribosomes, and granules. Mitochondria generate energy (in the form adenosine triphosphate [ATP] synthesis) by the oxidation of nutrients, and they contain the enzymes of the tricarboxylic acid (Krebs) cycle and for fatty acid oxidation and oxidative phosphorylation. In response to toxic insults they release enzymes that cause apoptosis. Mitochondria can replicate independently and code for the synthesis of some of their proteins; inheritance of mitochondrial DNA is maternal, and mitochondrial DNA defects cause a variety of diseases. See illustration and Plates 11 and 12. mitochondrial adj

Transmission electron micrograph of a mitochondrion.