EUKARIOTNY ORGANISMS

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EUKARIOTNY ORGANISMS

(Greek eu is good + karyon a kernel; synonym: eukaryotes, evkariota, nuclear organisms) — organisms, cells to-rykh have morphologically isolated kernel separated from cytoplasm by own cover and containing a species-specific set of chromosomes. At division of eukaryotic cells affiliated kernels are formed by a mitosis (see) and (or) meiosis (see).

All animal species belong to eukariotny organisms, mushrooms and plants except for bacteria and blue-green «seaweed» (blue-green algae) which are prokariotny organisms (see) and armor-clad flagellates — dinofla-

gellit, belonging to mezokariot-ny organisms.

In spite of the fact that in the taxonomical relation E. lakes are very different and include both the highest vertebrata, and one-celled (protozoa, yeast, nek-ry cabbage-weeds), on cytostructures nomas level all E. lakes have a number of the signs allowing to differentiate accurately them from prokariotny organisms.

In addition to a kernel most idiosyncrasies of a structure of eukaryotic cells are a complex system of the membranes creating in cytoplasm an endoplasmic reticulum (see), Golgi's complex (see Golgi a complex), mitochondrions (see) and plastids (at plants), existence of a cytoskeleton, sokratitelny vacuoles, lysosomes (see).

Extensive network of membranes in a cell E. the lake allows to localize various metabolic reactions in strictly certain sites of cytoplasm. On membranes of an endoplasmic reticulum secretory proteins, phospholipids and nek-ry other connections are synthesized, membranes of mitochondrions and plastids serve as the place of energy balance, Golgi's complex provides secretion of various proteins to the environment. The cytoskeleton presented by microtubules, microfilaments and microfibrils (see the Cell), performs basic and sokratitelny functions — provides preservation with a cell of a certain form and its movement.

In the biochemical relation E. lakes are more uniform, than prokariotny organisms. As food all E. lakes are subdivided on heterotrophs, to-rye receive from the environment ready organic compounds (sugar, amino acid, etc.), and the fototrof synthesizing these organic compounds from carbon dioxide gas and water in the course of photosynthesis (see). To the first animals and mushrooms, treat the second — green plants. Among prokariotny organisms in addition to heterotrophs and fototrof there are prototrophs synthesizing complex organic compounds from simple and also the hemotrofa using energy of chemical changes for synthesis of organic compounds (see Bacteria). The main sources of energy (ATP) in cells E. lakes are processes of glycolysis, oxidizing phosphorylation, and at green plants also photosynthesis. Prokariotny organisms for obtaining energy use much wider range of aerobic and anaerobic processes.

EUPHYLLINUM 385


Genetic device E. the island is presented by several chromosomes (see) which are localized in a kernel. Each chromosome E. the lake supports one the linear DNA thread, continuous throughout all chromosome, packed by means of histones (see) into a consecutive number of globular structures — nucleosoma. Chromosome number in a cell is a species-specific sign, and sex cells (ova and spermatozoa) have an unary (haploid) set of chromosomes. After merge of sex cells in the course of fertilization (see) the zygote and all somatic cells of metazoans and the higher plants developing from it contain a double (diploid) set of chromosomes, and nek-ry cells (e.g., many ferruterous cells) — polyploid.

Distinctiveness E. the lake is considerable excess of DNA in comparison with necessary quantity for coding (see. Genetic code) of all proteins of an organism. This surplus is caused by presence at DNA of a large number of large, average and small blocks of the repeating sequences of nucleotides, to-rye alternate with the unique and rare sequences of the nucleotides corresponding to certain proteins (see Chromatin).

Important difference E. the lake from prokariotny organisms is ek - zones - intronnaya the organization of many genes. Within sites of the chromosomes corresponding to separate structural genes (see the Gene), the sequences of nucleotides coding the amino-acid sequences (exons) alternate with not coding sequences (introns). Primary product of a transcription (see) is synthesized both on ekzonny, and on an intron-nykh sites of a gene, and then is exposed to processing (maturing): by means of special enzymes the pieces corresponding Nitron are removed, and corresponding to exons — connect, forming mature MRNK. Among the lowest organisms exon-intronnaya the organization of genes is revealed only at separate viruses of animals (SV-40, adenoviruses).

Bibliography: The East To. and Sumner of E. Hromosom of an eukaryotic cell, the lane, with English, M., 1981; Bochkov N. P., 3 ah and r about in And., T., and Ivanov>

V. I. Meditsinskaya of the geneticist, M., 1984; In and l - whether To. and Detye V. Biologiya, the lane with English, M., 1975; Gershenzon S. M. Fundamentals of modern genetics, Kiev, 1983; Ham R. G. and. V e about m e t t M. J. Mechanisms of development, St Louis a. o., 1980. „V. I. Ivanov.

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