| 单词 | collagen | |||
| 释义 | collagencol·la·genC0476400 (kŏl′ə-jən)collagen(ˈkɒlədʒən)col•la•gen(ˈkɒl ə dʒən)n. col·la·gen(kŏl′ə-jən)collagen
collagencollagen(kŏl`əjən), any of a group of proteins found in skin, ligaments, tendons, bone and cartilage, and other connective tissueconnective tissue,supportive tissue widely distributed in the body, characterized by large amounts of intercellular substance and relatively few cells. The intercellular material, or matrix, is produced by the cells and gives the tissue its particular character. ..... Click the link for more information. . Cells called fibroblasts form the various fibers in connective tissue in the body. The fibroblasts produce three types of fibers to form the ground substance: collagen, elatin, and the reticulum. Collagen consists of groups of white inelastic fibers with great tensile strength. These fibers include fine fibrils, which are composed of even finer filaments, visible only through the electron microscope. Collagen protein contains an unusually high percentage of the amino acids prolineproline , organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. ..... Click the link for more information. and hydroxyproline. X-ray diffraction studies provide evidence that the protein forms a wavy band, a coiled chain with periodic, i.e., repeating, arrangement of its amino acids. Cartilage is composed of fibrous collagen in an amorphous gel. The organic (nonmineral) content of bone is made up largely of collagen fibers with calcium salt crystals lying adjacent to each segment of the fiber; the fibers and salt crystals combined form a structure with compressional and tensile strength comparable to that of reinforced concrete. A group of diseases, often termed collagen, or connective tissue, diseases, involve a variety of alterations in the connective tissue fibers; rheumatoid arthritis, rheumatic fever, lupus, and scleroderma are included in this group. Some of these diseases may involve an autoimmune response, in which the immune mechanism injures or destroys the individual's own tissues (see immunityimmunity, ability of an organism to resist disease by identifying and destroying foreign substances or organisms. Although all animals have some immune capabilities, little is known about nonmammalian immunity. ..... Click the link for more information. ). Collagen dissolved in boiling water becomes denatured to form gelatingelatin or animal jelly, foodstuff obtained from connective tissue (found in hoofs, bones, tendons, ligaments, and cartilage) of vertebrate animals by the action of boiling water or dilute acid. ..... Click the link for more information. . CollagenThe major fibrous protein in animals, present in all types of multicellular animals and probably the most abundant animal protein in nature. It is estimated that collagen accounts for about 30% of the total human body protein. Collagen is located in the extracellular matrix of connective tissues. It is part of the interacting network of proteoglycans and proteins that provides a structural framework for both soft and calcified connective tissues. By self-associating into fibrils and by binding to proteoglycans and other matrix components, collagen contributes to tissue integrity and mechanical properties. Collagen interacts with cells through the integrin cell receptors and mediates cellular adhesion and migration. Important roles for collagen have been identified in development, wound healing, platelet aggregation, and aging. Its commercial importance in leather and the production of gelatin and glue have long been recognized. More recently, it is being used as a basis for biomaterials. Examples of its biomedical applications include injectable collagen to lessen facial wrinkles and defects; surgical collagen sponges to increase blood clotting; and artificial skin for the treatment of burns. The classification of an extracellular matrix protein as a collagen is based on the presence of a domain with a distinctive triple-helical conformation. The collagen triple helix consists of three polypeptide chains supercoiled about a common axis and linked by hydrogen bonds. At least 19 distinct molecules have been classified as collagens, and specific types are associated with particular tissues. The most prevalent and well-studied collagens belong to the fibril-forming or interstitial collagen family. The molecules in a fibril are covalently cross-linked by an enzymatic mechanism to strengthen and stabilize them. Inhibition of the enzyme involved in cross-linking results in a dramatic decrease in the tensile strength of tissues, a condition known as lathyrism. Type I is the most common fibril-forming collagen. Its fibrils make up the mineralized matrix in bone, the strong parallel bundles of fibers in tendon, and the plywoodlike alternating layers in the transparent cornea. Type II is the major fibril-forming collagen in cartilage, while type III is found in blood vessels and skin, together with type I. Basement membranes, which serve to separate cell layers and act as filtration barriers, contain a distinctive group of collagens, denoted as type IV collagens, which are organized into a network or meshlike sheet structure. In the kidney glomerulus, the network based on type IV collagen acts as a filter to determine which molecules will pass from the blood into the urine. See Bone, Connective tissue An orderly breakdown of collagen is necessary during development and tissue remodeling. For instance, following childbirth, the uterus reduces in size, which involves a massive degradation of collagen. An abnormal increase in the degradation of cartilage collagen is seen in osteoarthritis. Collagen breakdown also appears to be essential for tumor metastases. A number of hereditary diseases have been shown to be due to mutations in specific collagen genes. Osteogenesis imperfecta (brittle bone) disease is characterized by fragile bones and is due to mutations in type I collagen. Some cartilage disorders are caused by mutations in type II collagen. Ruptured arteries are found in Ehlers-Danlos syndrome type IV, which arises from mutations in type III collagen. Collagena fibrillar protein of the scleroprotein group; the principal component of the collagenous fibers of the connective tissues in animals. Collagen molecules (length, approximately 3,000 Å; width, 15 Å) consist of three interwined helical polypeptide chains. The primary structure of the collagen molecule is characterized by frequent repetition of a glycyl-prolyl-oxyprolyl sequence (about one-third of all amino acid residues), which influences the configuration of the chains. The collagen in mature fibers is insoluble in water and organic solvents and soluble in 10-percent alkaline solution. A part of the collagen of immature fibers (procollagen, or tropocollagen) is soluble in weak acid. Collagen fibers undergo marked contraction when heated in water; with prolonged heating, they are denatured and turn to gelatin. Collagen constitutes about a third of all protein in the body. It is an important structural component of connective tissue, tendons, ligaments, cartilage, skin, bones, and fish scales; its function is chiefly supportive. There is no collagen in plants. Tannins increase the resistance of collagen fibers to chemical, physical, and bacterial influences—the basis for tanning hides and furs. REFERENCESFinean, J. Biologicheskie ul’trastruktury. Moscow, 1970. (Translated from English.)Treatise on Collagen, vols. 1–2. Edited by G. N. Ramachandran and B. Gould. New York, 1967–68. V. O. SHPIKITER collagen[′kä·lə·jən]collagencollagencollagen[kol´ah-jen]The basic components of connective tissue are cells and extracellular protein fibers embedded in a matrix or ground substance of large carbohydrate molecules and carbohydrate-protein complexes called mucopolysaccharides. For the sake of clarity and organization, collagen diseases may be divided into two major groups: (1) those that are genetically determined and are a result of structural and biochemical defects, and (2) those that are acquired and in which immunological and inflammatory reactions are taking place within the tissues. Among the first group are those diseases caused by a lack of a specific enzyme necessary for proper storage and excretion of one or more mucopolysaccharides. Also included in this group are osteogenesis imperfecta, Ehlers-Danlos syndrome, and Marfan's syndrome. These disorders are distinguished by structural defects affecting the formation of the extracellular fibers called collagen. Acquired connective tissue diseases are believed to develop as a result of at least two causative factors: a genetic factor and an abnormal immunological response. The exact role of these factors in the development of connective tissue diseases has not been firmly established, but there is strong evidence that immunological mechanisms are involved. Examples of collagen diseases that are most probably the result of an aberration of the immunological reactions that mitigate injury and inflammation of connective tissues are systemic lupus erythematosus, scleroderma, rheumatoid arthritis, rheumatic fever, polymyositis, and dermatomyositis. col·la·gen(kol'lă-jen),See also: collagen fiber. collagen(kŏl′ə-jən)collagenA fibrous protein that provides strength and elasticity to skin, bones, cartilage and connective tissues.col·la·gen(kol'ă-jen)See also: collagen fiber Synonym(s): ossein, osseine, ostein, osteine. collagenAn important protein structural element in the body. Collagen fibres are very strong and, formed into bundles which are often twisted together, make up much of the connective tissue of the body. Bones are made of collagen impregnated with inorganic calcium and phosphorus salts. Vitamin C is necessary for the cross-linking and full strength of the collagen molecule.collagena fibrous protein that forms the white fibres of vertebrate CONNECTIVE TISSUE. These have a high tensile strength, e.g. tendons, but are not elastic. Collagen tissues consist of a glycoprotein matrix containing densely packed collagen fibres. The basic structural unit consists of three POLYPEPTIDE chains coiled round each other to form a triple helix, joined by hydrogen bonds. There are various different types of collagen, distinguished by the ability of the helical and non-helical regions to associate into fibrils (for example type I, II, III), to form sheets (for example type IV), or to cross-link different collagen types (for example type VI, IX). Most collagen is fibrillar. Type IV is unique to the BASAL LAMINA.Collagencollagencol·la·gen(kol'ă-jen)collagen
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