Mitochondria in cell life and death

The mitochondrion represents a unique organelle within the complex endomembrane systems that characterize any eukaryotic cell. It is realistic to state that complex life on earth has been made possible through the acquisition of mitochondria which provide an adequate supply of substrates for energy-expensive tasks. Higher multicellular organisms have indeed high-energy requirements necessary to carry out complex functions, such as muscle contraction, hormones and neurotransmitters synthesis and secretion, in addition to basal cellular metabolism (biomolecules synthesis and transformation, maintenance of ionic gradients across membrane, cell division). Mitochondria can fulfill this huge energy demand thanks to their extraordinary biosynthetic capacities: every day, mitochondria of a single human being can recycle up to 50 Kg of ATP. To further underline the relevance of these subcellular structures, one can also consider how these organelles have affected the physiology of the whole organism: lungs, heart, and circulatory system have evolved essentially to provide molecular oxygen to mitochondria, which consume about 98% of the total O2 we breathe. However, beyond the pivotal role they play in ATP production, a whole new mitochondrial biology has emerged in the last few decades: mitochondria have been shown to participate in many other aspects of cell physiology such as amino-acid synthesis, iron-sulphur clusters assembly, lipid metabolism, Ca2+ signaling, reactive oxygen species (ROS) production, and cell death regulation. © 2007 Springer-Verlag Italia.