Basic role of mitochondrial network dynamics in cell maintenance termed mitochondrial quality control. Mitochondrial fission separates dysfunctional (red) from functional (blue) mitochondria. Refusion of dysfunctional mitochondria to the mitochondrial network is prevented and dysfunctional mitochondria are removed and recycled by mitochondrial autophagy (A). If a cell is stressed (yellow arrows in B and C), mitochondria fuse in order to protect themselves and to warrant that they are still functional (B). If the stress prevails, mitochondrial fusion is prevented, mitochondria fragment, and mitochondria signal their stressed host cell to undergo cell death thereby removing the whole cell from the organism (C).