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A mitochondrion (mitochondria are the plural) is an organelle, the key function of which is to generate ATP (adenosine triphosphate) by oxidative phosphorylation via the mitochondrial respiratory chain, providing a key energy source for the eukaryote cell. They also have an important role in cell signalling, particularily during apoptosis. Mitochondrion can divide and mitochondria can fuse. This capacity is important in maintaining effective mitochondrion.

Info bulb.pngMitochondria have, and express, their own DNA because their evolution is from aerobic bacteria, which became endosymbionts in eukaryotic cells. The bacterium was able to further oxidise partially oxidised nutrients in the host cell, and produced an excess of ATP. A similar process accounts for chloroplasts in plant cells.

Mitochondrial DNA is inherited entirely from the mother (apart from in a few isolated examples of academic interest). Spermatozoa have only 22 to 28 mitochondria, while an ovum has thousands, and actively destroys paternal mitochondria during fertilisation. Bryan Sykes argues in his book, Adam's Curse, that this mechanism is required to prevent mitochondria competing for dominance in the cell. This maternal inheritance can help indicate the line of descent, back to "Mitochondrial Eve".

Metabolic Pathways in Mitochondria

Disease due to Mitochondria

The mtDNA results in some specific classic mitochondrial genetic diseases transmitted through the maternal line, but there is even more potential for pathology than this and you should see mitochondrial diseases.