From Big Medical Encyclopedia

SYMMETRY (Greek symmetria proportionality, a proper correlation) — the structural characteristic, edges can be inherent in any material bodies and consists in property of an object to be combined with itself at exchange of places jointly and (or) its specularly equal parts. There is also more general understanding of S. as properties of an invariance (invariancy) of the nek-ry parties, the phenomena, processes, the relations of material objects (including and the laws of nature) concerning some group of transformations (e.g., in time, space).

The greatest contribution to studying of the nature of S. is made by a crystallography (see. Crystals ). Use of the approach based on idea of S. in combination with methods of a crystallography, a crystal chemistry, stereochemistry, molecular biology and other sciences gave the chance to decipher a thin structure of proteins, nucleinic to - t, viruses and others biol. objects.

The page is property relative therefore in any natural objects, including biological, S. is never carried out with an absolute accuracy and all biol. elements are inherent in systems asymmetries (see). However if deviations from absolute S. are not big and have not systematic character, then objects are perceived as symmetric even then when these deviations are visible. At the same time, if in macromolecules (e.g., DNA) S. of the components making them is defined (though it is not absolute), then at the subcellular level C. is defined not by a form and a relative positioning of macromolecules, but kinetic characteristics of process of growth. In a bigger degree it belongs to organisms at all levels of an evolutionary ladder. At the lowest levels of development of wildlife for biol. systems cubic or screw S. Bolshinstvo of so-called spherical viruses actually is characteristic have the form of an icosahedron (20-grannik) and possess axes of Page 5,3 and the 2nd order. Nek-ry viruses (phage) have the form of an octahedron and according to axis 4, 3, and the 2nd order. S. of the screw is inherent to a fibrous casing of vegetable viruses of a rod form. At higher steps of evolution freely living unicells (e.g., staphylococcus) are characterized by S. of a sphere and possess infinite number of axes C. of an infinite order and infinite number of the planes C. Similar S. spherical metaphytes, napr, nek-ry radiolarias possess. Spherical S. of such organisms can be caused by benefits of rotary motion for catching from the environment of food. The animals who are characterized by a sedentary life have beam, or radial, S. Nek-rye coelenterates possess 4 or 6 planes C. For mammals, Crustacea, fishes, birds and insects existence bilateral, or bilateral is characteristic, S. (see. Bilateralism ). Its obligatory element is existence of one plane C. and one axis of symmetry of the 2nd order. Bilateral S.'s acquisition is connected with benefits of the active progress necessary at questing.

By page it is connected also with existence of so-called enantiomorphism (i.e. a pravizna and leftism of figures), at Krom there are specularly equal figures of the same S. (e.g., amino acids, sugars, alkaloids D a L-form, etc.). Enantiomorphism of chemical substances has big biol. value (see. Isomerism ). Enantiomorfny modifications (D a L-form) exist at flowers, leaves of plants, sinks of mollusks and are reflection of interaction of live organisms with the environment.

See also Asymmetry .

Bibliography: Kasinov V. B. About symmetry in biology, L., 1971; it, Biological isomerism, L., 1973; At r-mantsev Yu. A. Simmetriya of the nature and the nature of symmetry, M., 1974; Shubnikov A. V. and To about p c and to V. A. Simmetriya in science and art, M., 1972; Caspar D. L. and. To lug A. Physical principles in the construction of regular viruses, Cold Spr. Harb. Symp. quant. Biol., v. 27, p. 1, 1962.

S. M. Klimenko.