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Mitochondria

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Mitochondria

Mitochondria are responsible for energy production. They are also the responsible location for which respiration takes place. Mitochondria contain enzymes that help convert food material into adenosine triphosphate (ATP), which can be used directly by the cell as an energy source. Mitochondria tend to be concentrated near cellular structures that require large inputs of energy, such as the flagellum. The role of the mitochondria is very important in respiration.

In the presence of oxygen, pyruvate or fatty acids, can be further oxidized in the mitochondria. Each mitochondrion is enclosed by two membranes separated by an intermembrane space. The intermembrane space extends into the folds of the inner membrane called cristae which dramatically increase the surface area of the inner membrane. Cristae extend into a dense material called the matrix, an area which contains RNA, DNA, proteins, ribosomes and range of solutes. This is similar to the contents of the chloroplast stroma and like the chloroplast, the mitochondrion is a semi-autonomous organelles containing the machinery for the production of some of its own proteins. The main function of the mitochondrion is the oxidation of the pyruvate derived from glycolysis and related processes to produce the ATP required to perform cellular work.(Campbell
182-9)
Pyruvate, or fatty acids from the breakdown of triglycerides or phospholipids, pass easily through pores in the outer mitochondrial membrane made up of a channel protein called porin. The inner membrane is a more significant barrier and specific transport proteins exist to carry pyruvate and fatty acids into the matrix. Once inside the matrix, pyruvate and fatty acids are converted to the two carbon compound acetyl coenzyme A (acetyl CoA). For pyruvate this involves a decarboxylation step which removes one of the three carbons of pyruvate as carbon dioxide. The energy released by the oxidation of pyruvate at this stage is used to reduce NAD to NADH. (185)
The C2 acetyl CoA is then taken into a sequence of reactions known as
Krebs cycle which completes the oxidation of carbon and regenerates an acceptor to keep the cycle going. The oxidation of the carbon is accompanied by the reduction of electron acceptors and the production of some ATP by substrate phosphorylation. The C2 acetyl CoA is coupled to oxaloacetate, a C4 acceptor in the cycle. The product is citrate a C6 compound. This first product, citrate, is the reason the cycle is sometimes called the citric acid or ticarboxylic acid cycle, referring it after the scientist whose lab most advanced our understanding of it, Sir Hans Krebs. (Comptons 160)
Two of the early reactions of the cycle are decarboxylations which shorten citrate to succinate a C4 compound.
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