The mitochondrion is commonly called the ‘powerhouse of the cell’. Mitochondria (plural form) are double membrane-bound organelle that produces energy (adenosine triphosphate (ATP)) for the basal metabolism of the cell in most of the eukaryotic organism.
Mitochondria require oxygen during the process of pyruvate breakdown and ATP synthesis. The end products of this process (oxidative phosphorylation/electron transport chain) are water and carbon dioxide. Major parts of mitochondria – the outer mitochondrial membrane, the inner mitochondrial membrane, the intermembrane space (space between the outer and inner mitochondria), the cristae (the folding of the inner membrane), and the matrix (the space in the inner membrane).
Kreb’s cycle and electron transport chain take place in the inner membrane producing 36 moles of ATP per mole of glucose. The final electron acceptor of this process is oxygen.
The origin and evolution of mitochondria and eukaryotes is an active area of research. A major theory to explain the origin of mitochondria is called the endosymbiotic theory (symbiogenesis or serial endosymbiotic theory). It states that the mitochondrion once was an independent prokaryote, closely related to bacteria. On the other hand, eukaryotes are thought to originate from archaea and somewhere along the way, they merged into bacteria. A symbiotic relationship between archaea and bacteria – eukaryotic cell and mitochondria. There are several theories explaining the mechanism by which this could have happened. Most popular and leading one is that the membrane of ancient archaea folded inwards and swallowed the bacteria in a process called phagocytosis. This long standing theory was recently challenged by a new idea published in Nature. The new proposal is that the membrane of archaea develops protrusions that surrounds the bacteria and eventually, making the bacteria part of its cell.
An interesting feature that these theories reflect is that mitochondria has its own DNA. Nuclear and mitochondrial DNA are thought to evolve separately and is most studied in evolutionary biology and phylogenetic studies. Mitochondrial and nuclear genes together give rise to cellular functions. There are several genetic disorders contributed by mitochondrial genes.
Image Credit : Mitochondria – Wikipedia