The mitochondries (of the Greek mitos , wire and chondros , grain) are Organite S (in organelles English ) intracellular of a size about the Micromètre (µm). Their physiological role is paramount, since it is in the mitochondries that the energy provided by the organic molecules is recovered then stored in the form of ATP, the primary source of energy for the cell, by the process of oxydative Phosphorylation.
HistoryIn 1857, Kölliker describes the aspects of mitochondrion in the Muscle. In 1890, Altmaan describes a technique of coloring of the mitochondries and postulates their metabolic autonomy and Génétique. In 1937, a German scientist, Hans Adolf Krebs, built a model which it called “citric acid cycle”. This cycle takes place in mitochondrion at the Eucaryotes. In 1940-43, Claude isolates the mitochondries in cells from the Foie. In 1948-50, Kennedy and Lehninger show that the Cycle of Krebs, the Beta-oxidation and the oxydative Phosphorylation take place all in mitochondrion. In 1978, Peter Mitchell obtains the Nobel Prize for its chimiosmotic theory. In 1981, Anderson and its team discover the genetic structure of human DNA mitochondrial. Finally, Boyer and Walker, them also, obtain the Nobel Prize for their studies on the structure and the operation of ATP synthétase.
StructureThe mitochondries have a dimension from 1 to 2 μm length and 0,5 to 1 μm broad. They are composed of double-layered phospholipidique, external and an intern, which delimit three mediums: extra-mitochondrial medium (Cytoplasm of the cell), inter-membrane space and the matrix.
the external membrane is made of 60% of proteins and 40% of polar lipids. It contains many proteins called Porine S (VDAC) which form aqueous channels through the membrane. The porine (transmembrane proteins composed of 16 layers béta forming the proteinic channels crossing the bimolecular layer of lipids) lets pass all the absorbent molecules of a molecular mass lower than 10.000 dalton S (anions, cations, the fatty-acids, the pyruvate, the nucleotides cross it).
- the internal membrane is much less permeable than the external membrane. It is made up of 75% of proteins and 25% of lipids. It contains in quantity a double phospholipide, the Cardiolipine, containing 4 fatty-acids making this membrane impermeable with the ions. The other molecules must pass through a conveyer to cross the internal membrane.
A mitochondrion can come only from the growth and division from another already existing mitochondrion. Normally, before the cellular division, the mitochondrion doubles its mass then is divided into two. They are also able to amalgamate between them. This division begin with the appearance of a furrow of division on the internal membrane. It takes place during all the interphase and requires the intervention of protein DRP1 (close to the dynamine). The Réplication of the DNA mitochondrial is not limited to the phase S of the cellular Cycle. The number of mitochondries per cell is controlled by the cellular activity. For example, a muscular cell at rest contains 5 to 10 times less mitochondries that a muscular cell activated permanently.
The fact that the mitochondrion has its own DNA, like the Chloroplaste S, makes lean for an exogenic origin: the mitochondrion would be the remote downward one of a bacterium which would have been " adoptée" by the first eucaryotes. This assumption, the Endosymbiose, was developed and argued by Lynn Margulis since 1966, then was supported by the discovery of the specific DNA of the mitochondries in 1980. The role of this remote bacterium is unknown. It seems that during the evolution the DNA of the “bacterium mitochondrion” underwent various evolutions, lost certain genes, sometimes with the profit of the DNA of the host cell. Parallel to this carryforward of the synthesis of certain proteins towards the host, this last developed an arsenal of translocases, enzymes allowing the transfer of these proteins towards the matrix mitochondriale.
The genome mitochondrialThe genetic material (DNA mitochondrial) of the mitochondrion (which is the only part of the animal cells to have its own DNA, in addition to the core) is often useful in research Phylogénétique S.
The genome mitochondrial is circular, at the man, it is composed of 16 569 pairs of bases and is associated with proteins. The organization is comparable with the nucleoid (or chromosome) bacterial. Its composition in bases is different from that of the DNA contained in the core of the cell (the two molecules cannot hybrider).
Approximately 990 proteins mitochondriales are coded by the nuclear genome. These proteins are imported inside the matrix mitochondriale thanks to complexes of importation (3 on the internal membrane, 2 on the external membrane), of the signals of addressing (present on proteins to be imported) and thanks to an energy contribution. Nevertheless, a share from approximately 10% is directly synthesized in the matrix by the mitoribosomes, starting from the DNA mitochondrial. Majority of the enzymatic complexes (ex: ATP-synthase) are formed by the juxtaposition of polypeptides synthesized starting from the DNA mitochondrial and of the DNA of the core. For proteins coming from the cytosol (internal fluid of the cell), they have an additional sequence (sequence of addressing from approximately 15 to 30 amino-acids located at the N-final end).
Mitochondriaux ribosomes or mitoribosomes are different from ribosomes of the cell: they are smaller (70S instead of 80S). This DNA is very reduced compared to any procaryotic genome so that it contains only one ten Gène S.
The genetic code employed for the synthesis is different from that used in the syntheses Cytosolique S; 4 Codon S on 64 have a different significance, example codon UGA is transcribed in the cytosol in codon stop but in matrix UGA is transcribed out of tryptophan. The DNA mitochondrial can be also retorted.
In the animals, at the time of the sexuée reproduction, the mitochondries of the spermatozoon do not pass, in general, in the Ovocyte. In other words, the totality of the mitochondries of cell-egg comes from the gamète female, and all the mitochondries of an individual are transmitted to him by his mother. The study of human DNA mitochondrial thus makes it possible to recall the genealogical relations between the individuals only according to the maternal way. Certain recent studies thus could describe an ancestral genome mitochondrial from which all the mitochondriaux genomes would go down from humanity. The individual female supposed who carried this Génome was called Eve mitochondriale. This very outstanding term remains however misleading, since if all the human ones go down from the Eve by their genome mitochondrial, they go certainly down from several thousands of contemporaries of this Eve for the remainder of their genes.
She is regarded as the “lung” of the cell, because it is there that are held the last stages of the respiratory cycle (in the presence of Oxygène, aerobe) which converts the energy of the organic molecules resulting from digestion (Glucose) into energy directly usable by the cell (ATP). In the event of absence of oxygen the cell uses the Fermentation in the cytoplasm to produce energy necessary to its operation, but it is a system much less effective, which degrades in an incomplete way the substrate (production of lactic acid giving place, for example, with phenomena of cramps).
It is in mitochondrion that are held the 2 last phases of the cellular Respiration: the Cycle of Krebs (in the matrix) and the Chain of transport of electrons (on the level of the internal membrane). The first stage, the Glycolysis, proceeds in the cellular cytoplasm. Via the Cycle of Krebs (thus in condition of aerobiosis), the mitochondrion allows, starting from a molecule of glucose, the production of 38 molecules of ATP.
It is noted that the mitochondries take part in the Apoptose (cellular death) with the cytochrome C. Moreover, they have also a function of concentration and storage of the ions calcium, sodium and potassium where they are stored in the form of opaque granules. One also finds gold, iron and osmium.
The diseases mitochondriales
- neurodégénératives Diseases
- (27 minutes): Genetics of mitochondrion at the paramécies
Simple: Mitochondria Zh-min-nan: Soàⁿ-lia̍p-tea
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