Mitochondrial processes are both static (a) and dynamic (b). (a) depicts the classical movement of electrons along complexes I–IV embedded in the inner mitochondrial membrane with the generation of a proton gradient (membrane potential). The proton gradient causes hydrogen ions to flow back into the mitochondrial matrix via complex V (ATP synthase), producing ATP in the process. (b) depicts the processes of mitochondrial fusion and fission. Mitochondria can undergo constriction and division (1), mediated by Drp1, which bonds and localizes to the constriction site via an interaction with the receptor-like protein Fis1 (2). During fusion, a tether of the Mfn1/2 to collateral mitochondrial Mfn1/2 conjoins the outer membranes. Opa1, an inner membrane GTPase protein, facilitates the fusion of the inner membrane, cristae formation, and unifying of compartments.
