Mitochondria are organelles (“little organs”) found in virtually all cells in the human, (and animal) body except red blood cells. There may be from 20 to 2500 per cell (4). Mitochondria are the energy generators of the cell. They typically produce 90% or more of all the ATP bioenergy made in the body (4). The production of ATP within the mitochondria occurs from the interaction of two metabolic cycles - the tricarboxylic acid (TCA) cycle, (also called the “Krebs” or “citric acid” cycle) and the oxidative phosphorylation (OXPHOS) electron transport chain (ETC) (4). The TCA cycle occurs in the matrix of the mitochondria, while the ETC is a series of five multi-enzyme complexes which form an integral part of the inner mitochondrial membrane (4). Products of the TCA cycle - NADH, FADH2, succinate - are connected to the ETC to activate the first two enzyme complexes (I and II), which transfer electrons down the chain, eventually combining oxygen and hydrogen to make water, and producing ATP at complex II (ATP synthase) (4). The mitochondrion is essential for life. It generates the energy (from the food we eat) that powers cellular activity, muscular activity, heart and brain activity, breathing, walking, talking etc. Without ATP there is no life, and without well-functioning mitochondria, there is (almost) no ATP.

One of the unique features of mitochondria is that they contain their own DNA - mitochondrial DNA (mtDNA). All the other DNA of a cell is found in the nucleus (nDNA). The mitochondrial DN is a closed circular molecule. It encodes 13 ETC enzyme proteins, 2 ribosomal RNAs, and 22 transfer RNAs, all needed to form the mitochondrial ETC protein synthesis system (5). The remainder of the ETC enzymes and other mitochondrial components are encoded by nDNA. Each mitochondrion contains 5 to 10 mtDNA molecules (6). A mitochondrion reproduces itself by first increasing in size through integration of newly synthesized molecules, then eventually dividing to form two mitochondria (7).