Mitochondria
From EvoWiki
Mitrochondria (s: Mitochondrion) are cell organelles found in most eukaryotic cells. Known as the "power houses" of the cell, mitochondria convert energy stores into "energy currency". Mitochondria are usually seen as rods, spheres, cylenders, threads or occasionally branched structures. Size varies, but on average is approximately 5 microns in length, and 0.5 microns wide.
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Function
Mitochondria are responsible for aerobic respiration. They use the energy stored in glucose and fatty acid molecules to turn adenosine monophosphate and adenosine diphosphate into adenosine triphosphate - a small molecule that can be easily and quickly broken down to release energy. ATP controls calcium levels in the cell. The mitochondria are only the site of tricarboxylic acid cycle ("Krebs cycle", which takes place in the mtrix) and oxidative phosphrylation (which takes part in the outer chamber and on the inner membrane). For more see: Respiration.
Structure
Mitochondria are bounded by a double membrane. The outer membrane is slightly granular, and of similar composition to eukaryotic cell membranes (plasmalemma). The inner membrane is invaginated with many infoldings called cristae, which partially compartmentalise the mitochondria and increase the surface area. The inner membrane attached stalked particles (approx. 10 nm diam) containing ATP synthetase (enzymes which add a phosphate to ADP), and form part of the oxidative phosphrylation pathway. The inner chamber, called the matrix, is semi-solid and contains respiritory enzymes, ribosomes and DNA (both of these are mitochondria specific and are more similar in structure to prokaryotic (bacterial) rather than eukaryotic ribosomes and DNA), and crystals of calcium and magnesium ions. The outer chamber, an 8nm gap between the membranes
Endosymbiotic theory
A number of features, such as mitochondrial DNA suggest that mitochondria are evolved from ancient purple bacteria which lived symbiotically with proto-eukaryotic cells. It is generally believed that before this event proto-eukaryotic cells got all their energy from glycolysis, though the evidence (many genes for aerobic respiration being present into the nucleus) could be interpreted as suggesting that the proto-eukaryotic cells were capable of aerobic repiration, but comparatively inneficiently.
See also
References, links & furthur reading
- Wikipedia: Mitochondria
- Becker, Kleinsmith & Hardin, 2000, The World Of The Cell, Benjamin Cummings; ISBN: 0805345477
- Harker, D.W., 2003, Cell Biology 1, UWE in house publication.
