Mitochondria: Ultrastructure, Dynamics, Biogenesis and Main Functions

Mitochondria are double membrane-bound organelles that possess their own genome encoding essential but minute part of mitochondrial proteome. The vast majority of mitochondrial proteins are nuclear-encoded and several complementary processes ensure proper targeting, import, processing, and assembly of these proteins into mitochondria. Coordination between the two genomes expression is essential for proper assembly and activity of the oxidative phosphorylation system, which play a key role in energy metabolism in the vast majority of eukaryotic cells. In vivo, mitochondria display a high degree of connectivity and mobility. Mitochondrial dynamics is an essential physiological process ensuring the proper localization of mitochondria at intracellular sites of high-energy demand. Beyond their role in energy metabolism, mitochondria are also involved in lipid, amino acid and nucleic acid syntheses and are essential for biosynthesis of iron-sulfur clusters, heme, and other prosthetic groups. Mitochondrial respiratory chain is an important site of ROS production and ROS level must be tightly controlled by various enzymes. Unbalance between ROS production and detoxification plays a key role in metabolic disorders. Mitochondrial activity is therefore essential to cell fate, and mitochondrial dysfunctions have been associated with metabolic disorders. This chapter gives a general introduction on mitochondrial properties and functions that will be developed further in subsequent specialized chapters.