What is Mitochondria and its research history

  • Mitochondria are organelles that are present in most cells and are covered by two layers of membranes. They are the energy-producing structure in cells and the main place for cells to carry out aerobic respiration. They are called "power houses". Its diameter is about 0.5 to 1.0 microns.

    Except for Entamoeba histolytica, Giardia lamblia, and several microsporidians, most eukaryotic cells more or less possess mitochondria, but their respective mitochondria are in terms of size, number, and appearance. All are different.

    Mitochondria have their own genetic material and genetic system, but their genome is limited in size and is a semi-autonomous organelle. In addition to supplying energy to cells, mitochondria are also involved in processes such as cell differentiation, cell information transmission and cell apoptosis, and have the ability to regulate cell growth and cell cycle.


    Morphological characteristics


    Mitochondria are spherical, rod-shaped, or filamentous particles of different sizes, generally 0.5-1.0μm, and 1-2μm in length. Under an optical microscope, they need special dyeing to distinguish them. [2] In animal cells, the size of mitochondria is limited by the level of cellular metabolism. Different tissues may produce abnormally enlarged mitochondria under different conditions, called "megamitochondria": the exocrine cells of the pancreas can be as long as 10-20μm; the size of mitochondria in neuronal cell bodies varies greatly, and some are also It may be as long as 10μm; the mitochondria of human fibroblasts are longer, up to 40μm. Studies have shown that in a low oxygen partial pressure environment, the mitochondria of certain plants such as tobacco can reversibly become giant mitochondria, which can reach 80 μm in length and form a network.



    Mitochondria are generally short rod-shaped or spherical, but vary depending on the biological species and physiological state. They can also be ring-shaped, thread-shaped, dumbbell-shaped, bifurcated, flat disc-shaped, or other shapes. The shape-forming protein mediates mitochondrial contact with the surrounding cytoskeleton in different ways, or the formation of different connections between the two membranes of mitochondria, which may be the reason why mitochondria present different shapes in different cells.



    The difference in the number of mitochondria in different tissues of different organisms is huge. Many cells have as many as thousands of mitochondria (such as 1,000 to 2,000 mitochondria in liver cells), while some cells have only one mitochondria (such as the large branched mitochondria of yeast cells). The mature red blood cells of most mammals do not have mitochondria. Generally speaking, the number of mitochondria in a cell depends on the metabolic level of the cell. The more active the metabolic activity, the more mitochondria in the cell.



    Mitochondria are distributed in the same direction as microtubules and are usually distributed in areas with vigorous cell function: such as in kidney cells close to capillaries, arranged in parallel or grid; in intestinal epidermal cells, they are distributed in two poles, concentrated at the top and base; in sperm Distributed in the central area of flagella. In the in vitro culture of oocytes, as the cells mature, mitochondria will develop from being distributed around the cells to evenly distributed. Mitochondria can use microtubules as guide rails in the cytoplasm, powered by motor proteins, and migrate to areas with strong functions.



    The chemical components of mitochondria mainly include water, protein and lipids, and also contain a small amount of small molecules such as coenzymes and nucleic acids. Protein accounts for 65% to 70% of the dry weight of mitochondria. The proteins in mitochondria are both soluble and insoluble. Soluble proteins are mainly enzymes located in the mitochondrial matrix and peripheral proteins of the membrane; insoluble proteins constitute the body of the membrane, part of which is mosaic protein, and some are enzymes. Lipids in mitochondria are mainly distributed in two layers of membranes, accounting for 20% to 30% of dry weight. Phospholipids in mitochondria account for more than 3/4 of total lipids. The amount of phospholipids in the mitochondrial membranes of different tissues of the same organism is relatively stable. Rich in cardiolipin and less cholesterol are the obvious differences in the composition of mitochondria from other cell membrane structures.



    From the outside to the inside, the mitochondria can be divided into four functional areas: the outer mitochondrial membrane (OMM), the mitochondrial membrane space, the inner mitochondrial membrane (IMM) and the mitochondrial matrix. The membranes on the outside of the mitochondria are parallel to each other, and they are all typical unit membranes. Among them, the outer mitochondrial membrane is smoother, which acts as the cell organelle boundary membrane; the inner mitochondrial membrane folds inward to form mitochondrial cristae, which bears more biochemical reactions. The two membranes separate mitochondria into two compartments. Between the two mitochondrial membranes is the mitochondrial membrane gap, and the mitochondrial matrix is wrapped by the mitochondrial inner membrane.


    Research history

    The study of mitochondria began in the late 1850s.

    In 1857, Swiss anatomist and physiologist Albert von Klick discovered granular structures in muscle cells. Other scientists found the same structure in other cells, confirming Klick's discovery. German pathologist and histologist Richard Altman named these particles "bioblasts" and in 1886 invented a staining method to identify these particles. Altman speculated that these particles may be independent living bacteria living in symbiosis in cells.

    In 1898, the German scientist Karl Benda was sometimes linear and sometimes granular because of these structures, so he used the two words corresponding to "line" and "particle" in the Greek language-"mitos" and "chondros"-to form the composition. "Mitochondrion" came to name this structure, and this name is still in use today. A year later, American chemist Leonor Michelis developed a method of staining mitochondria with reductive Jiana Green dye solution, and inferred that mitochondria are involved in certain oxidation reactions. This method was published in 1900 and popularized by American cytologist Edmund Vincent Cowdery. German biochemist Otto Heinrich Warburg successfully completed the crude extraction of mitochondria and isolated some respiratory enzymes that catalyze oxygen-related reactions, and proposed that these enzymes can be inhibited by cyanide (such as hydrocyanic acid) Conjecture.

    British biologist David Keeling explored the material basis of the redox chain in the mitochondria during the decade from 1923 to 1933 and identified the electron carrier in the reaction-cytochrome.

    Warburg was awarded the Nobel Prize in Physiology or Medicine in 1931 for "discovering the nature and mode of action of respiratory enzymes."

    A recent study from the University of Virginia in the United States shows that the mitochondria in animal and plant cells are actually parasitic bacteria. Early parasitic bacteria can provide energy to animals and plants. They exist as energy parasites in cells and are very beneficial to the host. Next-generation DNA sequence technology decodes the genomes of 18 types of bacteria, which are close relatives of mitochondria.



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