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单词 ribosome
释义

ribosome

enUK

ri·bo·some

R0231500 (rī′bə-sōm′)n. A structure composed of RNA and protein, present in large numbers in the cytoplasm of living cells and serving as the site for assembly of polypeptides encoded by messenger RNA.
[ribo(nucleic acid) + -some.]
ri′bo·so′mal (-sō′məl) adj.

ribosome

(ˈraɪbəˌsəʊm) n (Biochemistry) any of numerous minute particles in the cytoplasm of cells, either free or attached to the endoplasmic reticulum, that contain RNA and protein and are the site of protein synthesis[C20: from ribo(nucleic acid) + -some3] ˌriboˈsomal adj

ri•bo•some

(ˈraɪ bəˌsoʊm)

n. a tiny, mitten-shaped organelle occurring in great numbers in the cell cytoplasm and functioning as the site of protein manufacture. [1958] ri`bo•so′mal, adj.

ri·bo·some

(rī′bə-sōm′) A sphere-shaped structure within the cytoplasm of a cell that is composed of RNA and protein and is the site of protein synthesis. Ribosomes are often attached to the membrane of the endoplasmic reticulum. See more at cell.
Thesaurus
Noun1.ribosome - an organelle in the cytoplasm of a living cell; they attach to mRNA and move down it one codon at a time and then stop until tRNA brings the required amino acid; when it reaches a stop codon it falls apart and releases the completed protein molecule for use by the cell; "the ribosome is the site of protein synthesis"cell organ, cell organelle, organelle - a specialized part of a cell; analogous to an organ; "the first organelle to be identified was the nucleus"
Translations

ribosome

enUK

ribosome:

see cellcell,
in biology, the unit of structure and function of which all plants and animals are composed. The cell is the smallest unit in the living organism that is capable of integrating the essential life processes. There are many unicellular organisms, e.g.
..... Click the link for more information.
; nucleic acidnucleic acid,
any of a group of organic substances found in the chromosomes of living cells and viruses that play a central role in the storage and replication of hereditary information and in the expression of this information through protein synthesis.
..... Click the link for more information.
.

Ribosome

 

an intracellular particle concerned with protein biosynthesis that is found in the cells of all living organisms (bacteria, plants, and animals); each cell contains thousands or tens of thousands of ribosomes. Ribosomes are close to spherical in shape, although their outlines are complex and cannot be described by a simple geometric figure.

Two major classes of ribosomes are distinguished: 70S and 80S. The 70S ribosome has a molecular weight of about 3 × 106, a diameter of about 200-300 angstroms (Å), and a sedimentation coefficient Ribosomeof about 70 Svedberg units. The larger, 80S, ribosome has a molecular weight of about 4–5 × 106, a maximum diameter reaching 400 Å, and a sedimentation coefficient of about 80 Svedberg units. Ribosomes of the 70S class are characteristic of prokaryotes—cells that do not have a structured nucleus—including bacteria, actinomycetes, and blue-green algae, as well as of the chloroplasts and mitochondria of higher organisms. Ribosomes of the 80S class are found in the cytoplasm of all eukaryotes—organisms that have a structured cell nucleus.

Chemically, ribosomes are nucleoproteins that consist of ribonucleic acid (RNA) and protein. Ribosomes of the 70S class consist of 60-65 percent RNA and 40-35 percent protein, while ribosomes of the 80S class consist of about 50 percent RNA and 50 percent protein. The general principle of the structural organization of ribosomes is that they are composed of two unequal subparticles, or subunits, to which a ribosome may dissociate (for example, upon a decrease in the concentration of Mg2+ ions in a medium) and reassociate according to the formula

70S ⇄ 50S + 30S 80S ⇄ 60S + 40S

The large subunit (50S or 60S) consists of a high-polymer molecule of ribosomal RNA that has a molecular weight of 1.1-1.8 × 106, a low-polymer molecule of ribosomal RNA that has a molecular weight of 40,000, and several tens of protein molecules. The small subunit (30S or 40S) consists of a molecule of ribosomal RNA that exhibits high polymerism and has a molecular weight of 0.6-0.7 × 106 and from 20 (in 30S subunits) to 40 (in 40S subunits) various protein molecules.

The high-polymer ribosomal RNA binds proteins into a single ribonucleoprotein particle. It is experimentally possible to unwind ribosomes—the unit becomes more friable and the RNA unwinds into a strand. During this process, all proteins remain attached to the particle. Under other conditions, the sequential cleavage of proteins from RNA may be achieved; this process is known as the separation of ribosomes. This separation is reversible and under suitable conditions proteins and RNA spontaneously reunite into a ribonucleoprotein, which forms the native structure of a ribosome; this process is known as the self-assembly of ribosomes. The self-assembly of previously synthesized RNA and proteins is also believed to form ribosomes in cells.

Ribosomes have several functions in the synthesis of proteins, including the specific binding and retention of the components of the system that synthesizes proteins; these components include messenger RNA (mRNA), aminoacyl-transfer RNA (aminoacyl-tRNA), peptidyl-tRNA, guanosine triphosphate (GTP), and the protein translation factors EF-T and EF-G. Ribosomes also have catalytic functions, including the formation of peptide bonds and the hydrolysis of GTP. They also assist in the mechanical displacement of substrates, for example, mRNA and tRNA, and in translocation.

The functions of catalysis and the retention of components are distributed between two ribosomal subunits. The small ribosomal subunit contains segments that bind mRNA and aminoacyl-tRNA; it apparently has no catalytic functions. The large subunit contains both a catalytic segment that catalyzes the formation of the peptide bond and a center that participates in the hydrolysis of GTP. During protein biosynthesis, the large subunit retains the growing protein chain in the form of pepti-dyl-tRNA. Each subunit may perform its functions independently of the other subunit. The function of translocation, however, can only be accomplished by the whole ribosome and not by the individual ribosomal subunits.

REFERENCE

Spirin, A. S., and L. P. Gavrilova. Ribosoma, 2nd ed. Moscow, 1971.

L. P. GAVRILOVA and A. S. SPIRIN

ribosome

[′rī·bə‚sōm] (cell and molecular biology) One of the small, complex particles composed of various proteins and three molecules of ribonucleic acid which synthesize proteins within the living cell.

ribosome

enUK

ribosome

 [ri´bo-sōm] any of the intracellular ribonucleoprotein organelles concerned with protein synthesis, found either bound to cell membranes or free in the cytoplasm. They may occur singly or in clusters (polyribosomes). The genetic code is translated when ribosomes attach to messenger RNA.

ri·bo·some

(rī'bō-sōm), A granule of ribonucleoprotein, 120-200 Ǻ in diameter, that is the site of protein synthesis from aminoacyl-tRNAs as directed by mRNAs. Synonym(s): Palade granule

ribosome

(rī′bə-sōm′)n. A structure composed of RNA and protein, present in large numbers in the cytoplasm of living cells and serving as the site for assembly of polypeptides encoded by messenger RNA.
ri′bo·so′mal (-sō′məl) adj.

ri·bo·some

(rī'bŏ-sōm) A granule of ribonucleoprotein, 120-150 Å in diameter, which is the site of protein synthesis from aminoacyl-tRNAs as directed by mRNAs.

ribosome

A spherical cell ORGANELLE made of RNA and protein which is the site of protein synthesis in the cell by linking amino acids into chains. Ribosomes may be free or may be attached to the endoplasmic reticulum. During translation, ribosomes attach to MESSENGER RNA molecules and travel along them, synthesizing polypeptides as they go.

ribosome

a small particle (not an ORGANELLE) found in the cytoplasm of all cells, composed of protein and RIBOSOMAL RNA. Each ribosome is composed of two subunits of different sizes which sediment at different rates during centrifugation (see ULTRACENTRIFUGE). PROKARYOTES have ribosome with 70 S size and mass; EUKARYOTES have larger ribosomes with 80 S size and mass. Ribosomes bind to the 5′ end of MESSENGER RNA (see POLYNUCLEOTIDE CHAIN) and travel towards the 3′ end, with TRANSLATION and POLYPEPTIDE synthesis occurring as they go along. Frequently several ribosomes are attached to one piece of mRNA, forming a POLYRIBOSOME.

Palade,

George Emil, Romanian-U.S. cell biologist and Nobel laureate, 1912–. Palade granule - a granule of ribonucleoprotein, the site of protein synthesis from aminoacyl-tRNAs as directed by mRNAs. Synonym(s): ribosomeWeibel-Palade bodies - see under Weibel
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ribosome

enUK
  • noun

Words related to ribosome

noun an organelle in the cytoplasm of a living cell

Related Words

  • cell organ
  • cell organelle
  • organelle
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