mitochondria

"One two three four!"

Mitochondria are organelles found in eukaryotes which are responsible for the oxidation of energy-rich substances. They are oval and have a diameter of approximately 1.5 micrometers and width of 2 to 8 micrometers.

Mitochondria have their own DNA and are thought to have evolved when an early eukaryote engulfed some primitive bacteria, but instead of digesting them, harnessed them to produce energy. Human children inherit their mothers' mitochondria, and thus mitochondrial DNA has been useful in tracing human lineages.

Compare chloroplast.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. Used with permission. For further information see the BioTech homenode.

It is envisaged that the modern eukaryotic animal cell arose from the emergence of a nucleated cell dependent on glycolytic fermentation for its ATP supply and separately from the emergence of a nucleated bacterial cell, possessing a respiratory chain and therefore a more efficient method of producig ATP. Early in the evolutionary timescale, the nucleated cell either absorbed or was invaded by the bacterial cell. Initially, a stable endo-symbiotic relationship was established which conferred advantages over the free living nucleated cells or anucleated cells. Such an arrangement is seen even today in the giant amoeba Pelomyxa palustris, which lacks mitochondria but contains respiring endosymbiotic bacteria. During the evolution of eukaryotic cells the nuclear genome has absorbed most of the genome of the anucleated organism. The plant cell is probably a descendant of this cell, which some time early on in evolution, absorbed a second prokaryotic cell capable of carrying photophosphorylation.