![]() ![]() The two membranes present significant differences in lipid composition, characteristics and roles of the transmembrane proteins, permeability and shape and are the result of the endosymbiotic origin of the organelle. Mitochondria are surrounded by two phospholipidic membranes, the outer mitochondrial membrane (OMM) and the inner mitochondrial membrane (IMM), which divide the organelle into two spaces, the matrix and the intermembrane space (IMS). #Freeciv 2.4.2 codeThis is true in different species, the genetic code being different, for instance, between vertebrates and other metazoans, but it is a universal code in plants this implies that the change in the genetic code of mtDNA occurred several times during evolution and it cannot be the primary cause for the maintenance of mtDNA within the organelle. Finally, the mtDNA genetic code differs slightly from nuclear DNA, presenting different codons encoding for tryptophan and methionine and only two stop codons. ![]() Moreover, contrary to nuclear DNA, mtDNA is present in many copies in the cell, between 100 and 10,000 copies, proportionally to the energy demand of the specific tissue. In fact, apart from one non-coding region, called the displacement loop or D-loop, each gene is contiguous to the next one, albeit some are partly overlapped. Indeed, mitochondria contain their own genetic material, mtDNA, which maintains the typical features of bacterial DNA: it is a circular 16,569-base pairs (bp) double-stranded molecule, does not contain introns and is polycistronic. This theory was supported by the discovery in the 1960s of mitochondrial DNA (mtDNA) and an independent mitochondrial translation system. Moreover, the complexity of this condition makes it challenging to identify possible therapies or drug targets. As a consequence, it is difficult to find a common cause for mitochondrial diseases and, subsequently, to offer a precise clinical definition of the pathology. Primary mitochondrial diseases are associated with genetic mutations both in nuclear and mitochondrial DNA (mtDNA), affecting genes involved in every aspect of the organelle function. Mitochondrial defects are at the origin of a group of clinically heterogeneous pathologies, called mitochondrial diseases, with an incidence of 1 in 5000 live births. Indeed, dysfunctional mitochondria cannot provide the required energy to tissues with a high-energy demand, such as heart, brain and muscles, leading to a large spectrum of clinical phenotypes. The interest in this organelle has grown stronger with the discovery of their link to various pathologies, including cancer, aging and neurodegenerative diseases. Mitochondria are ubiquitous intracellular organelles found in almost all eukaryotes and involved in various aspects of cellular life, with a primary role in energy production. ![]()
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