RIBOSOMES

From Big Medical Encyclopedia

RIBOSOMES (synonym: Peleyda of a granule, RNP-granules) — the intracellular organellas providing synthesis of protein. Were for the first time described in 1955 by J. Peleyd. the term P. is offered by Roberts (R. Century of Roberts) in 1958

represent the dense spherical educations (to dia. apprx. 25 — 30 nanometers) consisting of big and small subunits. Part P. is in cytoplasm of a cell in a free look (free R.), other part — is attached to a membrane endoplasmic reticulum (see). During synthesis of protein P. combine in larger units — polysom, or polyribosomes. R.'s number in a cell depends on intensity of synthesis of protein.

On free R. the proteins going generally on local needs of a cell are synthesized. Protein synthesis, cosecreted cell (see), the hl is carried out. obr. connected R.; at the same time polypeptides come directly to cavities of an endoplasmic reticulum where are exposed to further modifications. In addition to participation in protein synthesis, R., as well as other intracellular organellas, participate in the regulatory mechanisms exerting impact on all cell.

Rubles consist of ribosomal RNA (RRNK) and protein (see. Nucleoproteids ), contents to-rykh differs depending on type of a cell (animal, vegetable or bacterial). RRNK are synthesized in kernel (see), in the same place, presumably, there is R.'s assembly, i.e. aggregation of RRNK with the synthesized in cytoplasm and ribosomal proteins, trasportiruyemy in a kernel.

R.'s subunits are in a condition of reversible dissociation association. At low concentration of ions of magnesium dissociation of subparticles prevails, strengthening of ions of magnesium leads to their association. Rubles of zooblasts dissociate on subparticles with coefficient of sedimentation 60S and 40S. The big subparticle contains 2 molecules RNA (28S and 5S) and about 40 molecules of protein, small consists of molecule RNA (18S) and 30 of molecules of protein.

the Diagrammatic representation of a structure of a ribosome and the process of synthesis of protein proceeding in it: I \small subparticle; II \big subparticle; And — the aminoacylic site; P — the peptidilny site; 1 — a codon of information RNA; 2 — an anti-codon acceptor RNA; 3 — acceptor RNA, entering a ribosome; 4 — amino acid; 5 — the kanalopodobny structure penetrating a big subparticle; 6 — a membrane of an endoplasmic reticulum; 7 — it is time in a membrane of an endoplasmic reticulum; 8 — synthesizable polypeptide; 9 — acceptor RNA, left a ribosome. Approaches a codon of information RNA acceptor RNA (TRNK) which anti-codon is complementary to this codon. Together with TRNK amino acid aminoacyl-TRNK which joins the aminoacylic site of a ribosome forms a complex. After formation of a peptide bond of the brought amino acid with the extended polypeptide chain of TRNK moves to the peptidilny site. At the same time the ribosome moves to length of one codon in the direction specified by an arrow, the following complex aminoacyl-TRNK joins the aminoacylic site, and TRNK of the pepti-dilny site leaves a ribosome. Synthesizable polypeptide is located in the kanalopodobny structure penetrating a big subparticle and after completion of synthesis separates from a ribosome and through a time in a membrane of an endoplasmic reticulum comes to system of intracellular transport where is exposed to further modifications.

The amino acids necessary for protein synthesis are brought by acceptor RNA (TRNK), and the program of synthesis is concluded in information, or matrix, by the RNA (IRNK) formed in a kernel of a cell and joining R. (see. Broadcasting ). In big subparticles (fig.) existence of kanalopodobny structure is supposed, and the RNA and polypeptides which are in this area are protected from effect of cellular enzymes (RNA az and proteases). Also existence in R. of two sites is supposed: aminoacylic (And), the complex acceptor RNA with amino acid (aminoacyl-TRNK) and peptidilny joins Krom (P) where TRNK after formation of a peptide bond between the amino acid brought by it and the extended polypeptide chain moves ahead. These processes are provided the peptidiltransferazy, being a part big subparticle and the sokratitelny function of the nek-ry proteins similar to a myosin possessing, apparently.

Synthesis of protein begins with association of a small subparticle of R. and initiating N-aminoatsil-TRNK with an initial codon (see. Genetic code ) on 5' - the end of IRNK. Then the big subparticle joins this complex, and the created R. begins to move ahead to Z '-to the end of IRNK. On the course of this process to A-site P. come next aminoacyl-TRNK in the sequence determined by codons of IRNK.

See also RNA .



Bibliography: De Robertis E., Novinsky V. and Saes F. Cytobiology, the lane with English, page 324, M., 1973; Lenindzher A. Biochemistry, the lane with English, page 304, M., 1976; M e c of l e r D. Biokhimiya, the lane with English, t. 3, page 227, M., 1980; Roland Zh. - To., Selosha A. and Seloshi. The atlas on cytobiology, the lane with fr., page 28, M., 1978; Spirin A. S. and Gavrilova JI. P. Ribosoma, M., 1971; R and 1 and-d e G. E. A small particulate component of the cytoplasm, J. biophys. biochem. Cy-tol., v. 1, p. 59, 1955; Ribosomes, ed. by M. Nomura and. lake, N. Y., 1974; R o-b e r t s R. B. The synthesis of ribosomal protein, J. theor. Biol., v. 8, p. 49, 1965.


I. E. Hesinonim

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