PROKARIOTNY ORGANISMS

From Big Medical Encyclopedia

PROKARIOTNY ORGANISMS (Latin pro instead of + grech karyon a kernel; synonym: prokariota, bacteria nuclear-free, pre-atomic organisms, anukleobionta, prototsita) — group microscopic, mainly one-celled, beings whose main sign is lack of the «true» kernel delimited from cytoplasm by a membrane. Carry to them mycoplasmas, gram-positive and gram-negative bacteria, archaebacterias. Items of the lake have a certain medical value: some of mycoplasmas and bacteria are causative agents of diseases of the person and animals, a number of bacteria is a part of intestinal microflora. Material substrate of heredity at P. of the lake is presented by the DNA thread (usually ring) localized in the central part of a cell and not delimited from cytoplasm by a membrane.

Items of the lake differ from organisms which cells possess a true kernel (i.e. from an eukaryote), not only lack of a true kernel, but also specific structure, structure and function of cell walls, membranes, absence in cells of mitochondrions, chlorolayers, sokratitelny vacuoles, lysosomes, Golgi's device and microtubules. Their characteristic property is ability to synthesis of such organic compounds as glycopeptides, lipopolisakharida, 16SpPHK, bifitanilny and dibifitanilny lipids, many antibiotics, enzymes.

The item of the lake possesses an important role in a circulation of substances in the biosphere. In particular, P. of the lake are capable to a mineralization of an organic residues, anaerobic photosynthesis, a metanoobrazovaniye, dissimilyatorny recovery of sulfates, elemental sulfur, its nedookislenny connections, etc.

lakes divide P. into 4 large groups — mycoplasmas, gram-positive bacteria (firmakuta), gram-negative bacteria (gratsilikuta) and archaebacterias representing separate phylogenetic branches of P. of the lake. They significantly differ with a structure and chemical structure of cell walls, membranes, the sizes of genomes, structure and the sequence of nucleotides in 16SpPHK, functional specificity of the genetic device of a transcription and broadcasting, specificity of structure and regulation of enzymes and coenzymes, etc.

Mycoplasmas is P. the lake of childbirth this. Mycoplasmataceae (see). Mycoplasmas are deprived of a cell wall and surrounded with a three-layered membrane cover.

The group of gram-positive bacteria (see) combines spore-forming aerobic bacteria (see. Anaerobe bacterias , Aerobes ), lactobacilli (see. Lactobacilli ) and some cocci (see).

The group of gram-negative bacteria is morphologically most various. It includes blue-green algae, or blue-green seaweed (see), anaerobic phototrophic bacteria, enterobakteriya, myxobacteria, the budding bacteria, prostekobakteriya, spirochetes (see), other heterotrophic sticks, sperilla (see), vibrioes (see), rickettsiae (see) and cocci (see).

Archaebacterias differ from other groups P. of the lake on structure of oligonucleotides in 16 Sp RNA, to a set of unique coenzymes, bifitanilny lipids markedly; have ability to a metanogenez; at them fixing of carbon dioxide gas is carried out by a special way. Carry metanobrazuyushchy bacteria, acidophilic sulfur-oxidizing bacteria of the sort Sulfolobus, an extreme drimophilus (Halobacterium) and thermoacidophilic mycoplasmas (Thermoplasma) to archaebacterias. Some researchers in general consider archaebacterias as the third form of development of life, a special kingdom of the live organisms different from a kingdom an eukaryote and eubakteriya.

The main genetic information necessary for growth, development and P.'s reproduction by the lake, is concentrated at them in one DNA ring thread having a pier. the weight (weight) from 0,5*10 9 (some mycoplasmas) to 8,6*10 9 (some blue-green algae). This structure received the name of a prokariotny (bacterial) chromosome. Feature of the organization of a prokara an aerial root of a genome consists also in lack of repeatedly repeating nucleotide sequences owing to what almost all genes are presented in it only in one copy. Chromosomal DNA prokariot is organized in cells in the form of the structure which received the name nucleoid (see. Bacteria ). In cells prokariot there are extra chromosomal genetic elements — plasmids (see), similar on molecular structure and a way of replication (see) from the main chromosomal DNA.

A number of types of P. of the lake is activators inf. diseases of the person; some gram-positive bacteria — causative agents of such diseases, as botulism (see), pneumonia (see), malignant anthrax (see), tuberculosis (see), etc.; gram-negative bacteria — causative agents of such diseases, as typhoid (see), gastroenteritis (see), gonorrhea (see), dysentery (see), diphtheria (see), meningitis (see), syphilis (see), tularemia (see), cholera (see), plague (see) etc.

Among archaebacterias of disease-producing forms it is not found.

Many gram-positive and gram-negative bacteria are used as producers of antibiotics (see), vitamins (see), enzymes (see), antineoplastic means and antiactinic substances.



Bibliography: Gusev M. V. and Mineeva L. A. Microbiology, M., 1978; Zavarzin G. A. Phenotypical systematics of bacteria, M., 1974; Steyniyer R., Edelberg E. and Ingram D. The world of microbes, the lane with English, t. 1 — 3, M., 1979; Schlegel G. The general microbiology, the lane with it., M., 1972; Bergey’s manual of determinative bacteriology, ed. by R. E. Buchanan a N. E. Gibbons, Baltimore, 1975; Fox G. E. a. o. The phylogeny of prokaryotes, Science, v. 209, p. 457, 1980; Gibbons N. E. a. Murray R. G. E. Proposals concerning the higher taxa of bacteria, Int. J. system. Bact., v. 28, p. 1, 1978; W about e s e C. R., M a g r u m L. J. a. Fox G. E. Archaebacteria, J. molec. Evolut., v. 11, p. 245, 1978.


V. I. Duda.

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