Fig. 1: Structure of mitochondria.
Mitochondria are characterized by two membranes that define three functional compartments. The outer mitochondrial membrane (OMM) acts as a barrier between the cytosol and the intermembrane space. The inner mitochondrial membrane (IMM), in turn, separates the intermembrane space from the mitochondrial matrix. In doing so, the IMM forms numerous invaginations into the matrix, the mitochodrial cristae. At the base of these cristae, the crista junction separates the IMM into crista membrane (CM) and inner boundary membrane (IBM), respectively, of which the latter runs largely parallel to the OMM, separated by the intermembrane space. The OMM is highly permeable to small solutes and contains proteins that allow larger molecules to pass. The IMM, however, acts as a tight diffusion barrier that only allows the passage of certain molecules via specific transport proteins. This enables the maintenance of a proton gradient between the intermembrane space and the matrix, which is critical for adenosine triphosphate (ATP) synthesis in the CM. While the matrix provides enzymes for citric acid cycle activity A, enabling the production of substrates for oxidative phosphorylation, the CM contains the respiratory chain protein complexes B that generate the ATP29,60,61,62. Graphics were in part produced by Vibe Fog Sporring.
