Mitochondria are essential organelles of most eukaryotic cells; they are membrane enclosed and are typically distributed throughout the cytosol of the cell. Their primary function is to convert the potential energy of food molecules into ATP that can then be utilized by the cell. Mitochondria consist of: an outer membrane, which encapsulated the entire structure; an inner membrane, which encapsulates a fluid-filled matrix; an intermembrane space between the inner and outer membranes, which is elaborately folded with shelf-like cristae that project into the matrix; and a small number if circular DNA molecules. In general, the outer membrane of the mitochondria consists of membrane proteins that are responsible for moving molecules and ions in and out of the organelle. The inner membrane, however is considerable more complex and is composed of five key membrane proteins: NADH dehydrogenase, Succinate dehydrogenase, Cytochrome c reductase (also known as the cytochrome bc1 complex), Cytochrome c oxidase, and ATP synthase.
For the mitochondria to produce ATP, the process of respiration must occur within the organelle. Scientists have discovered that this process comparable to the respiration cycle exhibited by the cell membrane of prokaryotic cells. Overall, the process of respiration involves the transfer of elections through a series of membrane-bound protein carriers (the electron transport chain). Electrons are then removed form the membrane carriers by reducing some terminal electron acceptor such as oxygen-in the case of aerobic respiration-or nitrogen, sulfate or carbon dioxide--such as in the case of anaerobic respiration. For the mitochondria, electron transport and phosphorylation occur in the inner membrane.