FIG. 12.

Mitochondrial dynamics and biological functions. Mitochondrial biogenesis starts the mitochondrial cycle by division of pre-existing organelles, and mitophagy ends it by degradation of impaired mitochondria. In between, mitochondria undergo several cycles of fission and fusion that generate multiple heterogeneous mitochondria or interconnected mitochondrial networks depending on the physiological conditions. Fused mitochondrial networks are important for the dissipation of metabolic energy and for complementation of mtDNA gene products to counteract the decline of respiratory functions in aging in heteroplasmic cells.