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Mitochondrion is cytoplasmic organelle located in most eukaryotic cells that has its own genome. As it is independent from genomic DNA it is rather well conserved. These organelles are responsible for the cellular metabolism, especially glycolysis, energy and heat production … Mitochondrion are inherited from the mother only and thus it does not follow Mendelian conditions.
Mitochondrion origin is still a controversial question, yet most scientists agree those mitochondria are the product of an endosymbiosis between a proteobacteria and a eukaryotic cell that happened about two billion years ago.
Mitochondrial DNA can be found in several different structures depending on what kind of cell they are found. It can be either circular, linear, double stranded or single stranded. In most mammals’ cells, mtDNA is circular and double stranded. It encodes 37 different genes which is rather low compared to genomic DNA (between 1000 and 40 000 genes in most of living things).
Figure 1 : Schématisation d'une mitochondrie
Figure 2 : Représentation de la transmission maternelle des mitochondries
Figure 3 : Schématisation de l'endosymbiose ayant eu lieu il y a 2 milliards d'années
Figure 4 : Représentation circulaire de l'ADN mitochondrial humain
Mitochondria have their own specific genetic code, whereas all other living things share the same universal genetic code. Mitochondria genome is constantly evolving and it will evolve differently for each organism leading to diversity among species. Thus mitochondrial genome can be used to identify species by “measuring” the amount of differences between two species and define the phylogenetic tree by identifying common ancestors.
Figure 5 : Structure d'un arbre phylogénétique obtenu par étude du génome mitochondrial
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