Mitochondria biochemical function

FIGURE 19-1 Biochemical anatomy of a mitochondrion. The convolutions (cristae) of the inner membrane provide a very large surface area. The inner membrane of a single liver mitochondrion may have more than 10,000 sets of electron-transfer systems (respiratory chains) and ATP synthase molecules, distributed over the membrane surface. Heart mitochondria, which have more profuse cristae and thus a much larger area of inner membrane, contain more than three times as many sets of electron-transfer systems as liver mitochondria. The mitochondrial pool of coenzymes and intermediates is functionally separate from the cytosolic pool. The mitochondria of invertebrates, plants, and microbial eukaryotes are similar to those shown here, but with much variation in size, shape, and degree of convolution of the inner membrane. 

Many particles pass through the membrane of a cell with the electrochemical energy gradient, but some against it. Adenosin triphosphate (ATP) is thought to provide the energy for this latter occurrence. An important biochemical reaction is, then, the endothermic formation of ATP by the phosphorylation process. The enzymes which are associated with this are found in the subcellular unit known as the mitochondrion. Electrochemical reactions may function here. 

Cytoehrome function is inseparable from that of mitochondria, and the inheritance of the cytochrome patterns of the petite and poky (see below) mutants has long been known to follow the 4 0 distribution of maternal or cytoplasmic inheritance, as opposed to the 2 2 distribution of chromosomal genes. That the biochemical machinery for cytoplasmic inheritance exists has been shown by the finding of the necessary genetic and protein-synthesizing components in the mitochondrion (for references, see [42,45,46]). It appears likely that the amount of intrinsically synthesized protein, although indispensable, is small compared to extrinsically produced material. 

The inner membrane of the mitochondrion accounts for 80-95% of the protein found in mitochondrial membranes and over 90% of the lipid. It is the site of the respiratory chain and the synthesis of ATP. It is this membrane, in conjunction with studies on transport through the plasma membrane, that has contributed most forcefully both to the viewpoint of the anisotropic organization of membrane structural elements and of biochemical events carried out by or in membranes. As regards mitochondria, the interaction of the inner membrane components in carrying out electron transport and oxidative phosphorylation is the focal investigative question both for mitochondrial function and for the organization of vectorial events in general. 

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