History of Mitochondria

History of Mitochondria

The mitochondria were first observed by Kolliker in 1850 as granular structures in the striated muscles. In 1888, he isolated them from insect muscles (which contain many slabs like mitochondria) and showed that they swelled in water and contain a membrane around them. In 1882, Flemming named them as the file. Richard Altmann developed a specific stain that had useful specificity for the mitochondria. He named this organelle, the bioblast. Altmann correctly speculated that bioblasts were autonomous elementary living particles that made a genetic and metabolic impact on the cells. The present name mitochondria were assigned by Benda(1897-98) to them. He stained mitochondria with alizarin and crystal violet. Michaellis (1900) used the supravital stain Janus green to demonstrate that mitochondria were oxidation-reduction sites in the cell. In 1912, Kingsbury suggested that the oxidation the oxidation reactions mediated by mitochondria were normal cellular processes. Otto Warburg(1883-1970), who is considered as ‘the father of respirometry’, in 1910 isolated mitochondria (‘large granules”) by low-speed centrifugation of tissues disrupted by grinding.Various steps of glycolysis were discovered by two German biochemists Embden and Meyerhof [GustavG.Embden (1874-1933);OttoF.Meyerhof(1884-1951)].Meyerhof got a Nobel prize in 1922 along with English biophysicist A.V.Hill,for the discovery of oxygen and metabolism of lactic acid in muscle (i.e.,production of heat in muscle).Lohmann (1931)discovered ATP in muscle.Lipmann(German biochemists in U.S. ;born 1899)discovered coenzyme A and showed its significance in intermediary metabolism. In 1941 , he introduced the concept of “high energy phosphate bonds” in bioenergetics. Warburg linked the phenomenon of ATP formation to the oxidation of glyceraldehyde phosphate. Meyerhof showed the formation of ATP from phosphopyruvate and Kalckar related oxidative phosphorylation to respiration. Sir Hans Adolph Krebs in 1973, worked out various reactions of the citric acid cycle. His contribution was remarkable , because ,up to that time radioactively labeled compounds were not available for biological studies and cellular sites of the reactions were not known with certainty. Krebs received the Noble Prize in 1953 along with Lipmann for his discovery of the citric acid cycle.

DISTRIBUTION OR LOCALIZATION

The mitochondria move autonomously in the cytoplasm, so they generally have uniform distribution in the cytoplasm , but in many cells, their distribution is very restricted. The distribution and number of mitochondria are often correlated with the type of function the cell perform. Typically mitochondria with many cristae are associated with mechanical and osmotic work situations, where there are sustained demands for ATP and where space is at a premium, e.g. in between muscle fibers, in the basal in the folding of kidney tubule cells, and in a portion of the inner segment of rod and cone cells of retina. Myocardial muscles cells have numerous large mitochondria called Sarcosomes, that reflects the great amount of work done by these cells.Since the work of hepatic cells is mainly biosynthetic and degradative,and work locations are spread throughout the cell,in these cells,it may be more efficient to have a large number of “low key”sources of ATP production distribution throughout the cell.Often mitochondria occur in greater concentration at work sites,for ,in the oocyte of Thyone Piraeus,rows of mitochondria are closely associated with RER membranes where ATP is required for protein biosynthesis.Mitochondria are particularly numerous in regions where ATP-drove osmotic work occurs,eg,brush border of kidney proximal tubules,the infolding of the plasma membrane of dogfish salt glands and Malpighian tubules of insects,the contractile vacuoles of some protozoans(Paramecium).Non-myelinated axons contain many mitochondria that are poor ATP factories since each has only a single crista.In this case,there is the great requirement for monoamine oxidase,an enzyme deaminates monoamines including neurotransmitters(acetylcholine).

The number of mitochondria in a cell depends on the type and functional state of the cell.It varies from cell to cell and from species to species. Certain cells contain the exceptionally large number of the mitochondrial e.g.,the Amoeba,Chaos chaos contains 50,000;eggs of sea urchin contain 140,000 to 150,000 and oocytes of amphibians contain 300,000 mitochondria.Certain cells,viz.,liver cells of rat contain only 500 to 1600 mitochondria.The cells of green plants contain less number of mitochondria in comparison to animals cells because in plant cells the function of mitochondria is taken over by the chloroplasts.Some algal cells may contain only one mitochondrion.

Shape

The mitochondria may be filamentous or granular in shape and may change from one form to another depending upon the physiological conditions of the cells.Thus,they may be of club,racket,vesicular,ring or round shape.Mitochondria are granular in primary spermatocyte or rat,or club-shaped in liver cells.

The mitochondria may be filamentous or granular in shape and may change from one form to another depending upon the physiological conditions of the cells.Thus,they may be of club,racket,vesicular,ring or round shape.Mitochondria are granular in primary spermatocyte or rat,or club-shaped in liver cells.

Time-lapse micro cinematography of living cells shows that mitochondria are remarkably mobile and plastic organelles,constantly changing their shape.They sometimes fuse with one another and then separate again.For example,in certain euglenoid cells,the mitochondria fuse into a reticulate structure during the day and dissociate during darkness.Similar changes have reported in yeast species,apparently in response to culture conditions.

Size.

Normally mitochondria vary in size from 0.5 um and,therefore,are not distinctly visible under the light microscope.Sometimes their length may reach up to 7um.

Structure

Each mitochondrion is bound by two highly,specialized membranes that play a crucial part in its activities.Each of the mitochondrial membranes is 6nm in thickness and fluid mosaic in ultrastructure. The outer membrane is quite smooth and has many copies of a transport protein called porin which forms large aqueous channels through the lipid bilayer.This membrane thus resembles a sieve that is permeable to all molecules of 10,000 daltons or less, including small proteins.Inside and separated from and separated from the outer membrane by a 6-8nm wide space is highly convoluted,forming a series of imploding,known as cristae,in the matrix space.

Thus,mitochondria are double membrane envelopes in which the inner membrane divides the mitochondrial space into two distinct chambers:1.The outer compartment,peri-mitochondrial space or the inter-membrane space between the outer membrane and inner membrane.This space is continuous into the core of the crests or cristae.2.The inner compartment,inner chamber or matrix space,which is filled with a dense,homogeneous,gel-like proteinaceous material,called mitochondrial matrix.The mitochondrial matrix contains lipids,proteins,circular DNA molecules,55S ribosomes and certain granules which are related to the ability of mitochondria to accumulate ions.Granules are prominent in the mitochondria of cells concerned with the transport of ions and water,including kidney tubule cells,epithelial cells of the small intestine,and the osteoblasts of bone-forming cells.Further,the inner membrane has an outer cytosol or C-face toward the per mitochondrial space and an inner matrix or M face toward matrix.

In general,the cristae of plant mitochondria are tubular,while those of animal mitochondria are tubular,while those of animal mitochondria are lamellar or plate-like(Hall,Flowers, and Roberts,1974),but,in many Protozoa and in steroid synthesizing tissues including the adrenal cortex and corpus luteum, they occurs as regularly packed tubules(Tyler,1973). The cristae greatly increase the area of the inner membrane,so that in liver cell mitochondria,the cristae membrane is 3-4 times greater than the outer membrane area. Some mitochondria ,particularly those from the heart,kidney, and skeletal muscles have more extensive cristae arrangements than liver mitochondria.In comparison to these,other mitochondria (e.g.,from fibroblasts,nerve axons, and most plant tissues)have relatively few cristae.For example,mitochondria in epithelial cells of carotid bodies(or glomus critical which are chemoreceptors,sensitive to changes in blood chemistry and lie near the bifurcations of carotid arteries)have only four to five cristae and mitochondria from non-myelinated axons of rabbit brain have only a single crista.

References

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Kotpal, R L. Modern textbook of Zoology. Meerut, India: Rastogi Publication, n.d.

Rastogi, S C. Cell, and Molecular biology. New Delhi: New Age International (P) Limited, 2001.

Verma, P S, and V K Agrawal. cell biology,Genetics,Molecular Biology,Evolution, and Ecology. New Dehli, India: S. Chand and company Ltd., 2012.