Mitochondria are eukaryotic intracellular organelles that still bear the signatures of their prokaryotic ancestor
and require nuclear assistance. They generously dispense energy to cells, but are also involved in several biosynthetic
processes, as well as in cell signalling pathways and programmed cell death.
Mitochondria are partitioned into four intra-organelle compartments: the outer membrane, the inner membrane, the
intermembrane space and the matrix. Each compartment contains a unique set of proteins and a personalised system for
guaranteeing protein homeostasis.
What follows is a survey of the function and topology of the multiple systems that operate the concerted action of protein
sorting and folding in the four mitochondrial compartments.