page_title: Mitochondrial biogenesis
section_title: Fusion and fission
hierarchical_section_title: Mitochondrial biogenesis / Fusion and fission
caption_attribution_description: English: The processes of fission and fusion reorganize the mitochondrial network
context_page_description: Mitochondrial biogenesis is the process by which cells increase mitochondrial mass. It was first described by John Holloszy in the 1960s, when it was discovered that physical endurance training induced higher mitochondrial content levels, leading to greater glucose uptake by muscles. Mitochondrial biogenesis is activated by numerous different signals during times of cellular stress or in response to environmental stimuli, such as aerobic exercise.
context_section_description: Mitochondria are highly versatile and are able to change their shape through fission and fusion events. Definitively, fission is the event of a single entity breaking apart, whereas fusion is the event of two or more entities joining to form a whole. The processes of fission and fusion oppose each other and allow the mitochondrial network to constantly remodel itself. If a stimulus induces a change in the balance of fission and fusion in a cell, it could significantly alter the mitochondrial network. For example, an increase in mitochondrial fission would create many fragmented mitochondria, which has been shown to be useful for eliminating damaged mitochondria and for creating smaller mitochondria for efficient transporting to energy-demanding areas. Therefore, achieving a balance between these mechanisms allow a cell to have the proper organization of its mitochondrial network during biogenesis and may have an important role in muscle adaptation to physiological stress.
  In mammals, mitochondrial fusion and fission are both controlled by GTPases of the dynamin family. The process of mitochondrial fission is directed by Drp1, a member of the cytosolic dynamin family. This protein forms a spiral around mitochondria and constricts to break apart both the outer and inner membranes of the organelle. On the other hand, the process of fusion is directed by different membrane-anchored dynamin proteins at different levels of the mitochondria. Fusion at the level of the outer mitochondrial membrane is mediated by Mfn1 and Mfn2 (Mitofusins 1 and 2), and fusion at the level of the inner mitochondrial membrane is mediated by Opa1. Multiple research studies have observed correlated increases between mitochondrial respiratory capacity with Mfn1, Mnf2, and Drp1 gene expression after endurance exercises. Therefore, it is supported that reorganization of the mitochondrial network in muscle cells plays an important role in response to exercise.
caption: The processes of fusion and fission allow for mitochondrial reorganization.
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