ribosome: Definition from Answers.com

Ribosomes are the cellular organelles that carry out protein synthesis, through a process called translation. They are found in both prokaryotes and eukaryotes, these molecular machines are responsible for accurately translating the linear genetic code, via the messenger RNA, into a linear sequence of amino acids to produce a protein. All cells contain ribosomes because growth requires the continued synthesis of new proteins. Ribosomes can exist in great numbers, ranging from thousands in a bacterial cell to hundreds of thousands in some human cells and hundreds of millions in a frog ovum. Ribosomes are also found in mitochondria and chloroplasts.

Structure

The ribosome is a large ribonucleoprotein (RNA-protein) complex, roughly 20 to 30 nanometers in diameter. It is formed from two unequally sized subunits, referred to as the small subunit and the large subunit. The two subunits of the ribosome must join together to become active in protein synthesis. However, they have distinguishable functions. The small subunit is involved in decoding the genetic information, while the large subunit has the catalytic activity responsible for peptide bond formation (that is, the joining of new amino acids to the growing protein chain).

In prokaryotes, the small subunit contains one RNA molecule and about twenty different proteins, while the large subunit contains two different RNAs and about thirty different proteins. Eukaryotic ribosomes are even more complex: the small subunit contains one RNA and over thirty proteins, while the large subunit is formed from three RNAs and about fifty proteins. Mitochondrial and chloroplast ribosomes are similar to prokaryotic ribosomes.

In spite of its complex composition, the architecture of the ribosome is very precise. Even more remarkable, ribosomes from all organisms, ranging from bacteria to humans, are very similar in their form and function. Recent breakthroughs in studies of ribosome structure, using techniques such as scanning, cryo-electron microscopy, and X-ray crystallography, have provided scientists with highly refined structures of this complex organelle. One particularly exciting conclusion from studies of the large subunit is that it is ribosomal RNA (rRNA), and not protein, that provides the catalytic activity for peptide bond formation. That is, it forms the chemical linkage between the amino acids of the growing protein molecule.

Synthesis

The synthesis of ribosomes is itself a very complex process, requiring the coordinated output from dozens of genes encoding ribosomal proteins and rRNAs. Ribosomes are assembled from their many component parts in an orderly pathway. In eukaryotes, rRNA synthesis and most of the assembly steps occur in a structure within the nucleus called the nucleolus. Eukaryotic ribosome synthesis is especially complicated, because the ribosomal proteins themselves are made by ribosomes in the cytoplasm (that is, outside of the nucleus), so they then must be imported into the nucleolus for assembly onto the nucleolus-derived rRNA. Once assembled, the nearly complete ribosomal subunits are then exported out of the nucleus and back into the cytoplasm for the final steps of assembly.

The exact details of the in vivo ribosome assembly pathway (the process of ribosome assembly within the living cell) are still under investigation. Assembly in eukaryotic cells involves not only the components of the mature particles, but also dozens of auxiliary factors that promote the efficient and accurate construction of the ribosome during its assembly. However, bacterial ribosomes can be constructed in vitro using purified ribosomal proteins and rRNAs. These ribosomes appear to function normally in in vitro translation reactions.

Ribosome Function

Translation of messenger RNA (mRNA) by ribosomes occurs in the cytoplasm. In bacterial cells, ribosomes are scattered throughout the cytoplasm. In eukaryotic cells, they can be found both as free ribosomes and as bound ribosomes, their location depending on the function of the cell. Free ribosomes are found in the cytosol, which is the fluid portion of the cytoplasm, and are responsible for manufacturing proteins that will function as soluble proteins within the cytoplasm or form structural elements, including the cytoskeleton, that are found within the cytosol.

Bound ribosomes are attached to the outside of a membranous network called the endoplasmic reticulum to form what is termed the "rough" endoplasmic reticulum. Proteins made by bound ribosomes are intended to be incorporated into membranes, or packaged for storage, or exported outside of the cell. Ribosomes exist either as a single ribosome (that is, one ribosome translating an mRNA) or as polysomes (two or more ribosomes sequentially translating the same mRNA in order to make multiple copies of the same protein).

Ribosomes have the critical role of mediating the transfer of genetic information from DNA to protein. Ribosomes translate this code using an intermediary, the messenger RNA, which is a copy of the DNA that can be interpreted by ribosomes. To begin translation, the small subunit first identifies, with the help of other protein factors, the precise point in the RNA sequence where it should begin linking amino acids, the building blocks of protein. The small subunit, once bound to the mRNA, is then joined by the large subunit and translation begins. The amino acid chain continues to grow until the ribosome reaches a signal that instructs it to stop.

Many of the antibiotics used in humans and other animals to treat bacterial infections specifically inhibit ribosome activity in the disease-causing bacteria, without affecting ribosome function in the host-animal's cells. These antibiotics work by binding to a protein or RNA target in the bacterial ribosome and inhibiting translation. In recent years, the misuse of antibiotics has resulted in the natural selection of bacteria that are resistant to many of these antibiotics, either because they have mutations in the antibiotic's target in the ribosome or because they have acquired a mechanism for excluding or inactivating the antibiotic.

Bibliography

Frank, Joachim. "How the Ribosome Works." American Scientist 86 (1998): 428-439

Garrett, Robert A., et al, eds. The Ribosome: Structure, Function, Antibiotics, and Cellular Interactions. Washington, DC: ASM Press, 2000

Karp, Gerald. Cell and Molecular Biology: Concepts and Experiments, 3rd ed. New York: John Wiley & Sons, 2002.

—Janice Zengel

Ribosomes read the sequence of messenger RNAs and assemble proteins out of amino acids bound to transfer RNAs.

A ribosome is a component of cells that synthesizes protein chains. It assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule.^[1]

One of the central tenets of biology, often referred to as the central dogma of molecular biology, is that DNA makes RNA makes protein.^[2]^[3] The DNA sequence in genes is copied into a messenger RNA (mRNA). Ribosomes then read the information in this mRNA and use it to create proteins. This process is known as translation; the ribosome translates the genetic information from the mRNA into proteins. Ribosomes do this by binding to an mRNA and using it as a template for determining the correct sequence of amino acids in a particular protein. The amino acids are attached to transfer RNA (tRNA) molecules, which enter one part of the ribosome and bind to the messenger RNA sequence. The attached amino acids are then joined together by another part of the ribosome. The ribosome moves along the mRNA, "reading" its sequence and producing a corresponding chain of amino acids.

Ribosomes are made from complexes of RNAs and proteins called ribonucleoproteins. Ribosomes are divided into two subunits. The smaller subunit binds to the mRNA, while the larger subunit binds to the tRNA and the amino acids. When a ribosome finishes reading a mRNA, these two subunits split apart. Ribosomes have been classified as ribozymes, because the ribosomal RNA seems to be most important for the peptidyl transferase activity that links amino acids together.

Ribosomes from bacteria, archaea and eukaryotes (the three domains of life on Earth), have significantly different structures and RNA sequences. These differences in structure allow some antibiotics to kill bacteria by inhibiting their ribosomes, while leaving human ribosomes unaffected. The ribosomes in the mitochondria of eukaryotic cells functionally resemble in many features those in bacteria, reflecting the likely evolutionary origin of mitochondria.^[4]^[5] The word ribosome comes from ribo nucleic acid and the Greek: soma (meaning body).

Together with Albert Claude and Christian de Duve, George Emil Palade was awarded the Nobel Prize in Physiology or Medicine, in 1974, for the discovery of the ribosomes.^[6] The Nobel Prize in Chemistry 2009 was awarded to Venkatraman Ramakrishnan, Thomas A. Steitz and Ada E. Yonath for discovering the detailed structure and mechanism of the ribosome.^[7]

Contents

1 Description
2 Biogenesis
3 Ribosome locations
- 3.1 Free ribosomes
- 3.2 Membrane-bound ribosomes
4 Structure
- 4.1 High-resolution structure
5 Function
6 See also
7 References
8 External links

Description

Archaeal, eubacterial and eukaryotic ribosomes differ in their size, composition and the ratio of protein to RNA. Because they are formed from two subunits of non-equal size, they are slightly longer in the axis than in diameter. Prokaryotic ribosomes are around 20 nm (200 Å) in diameter and are composed of 65% ribosomal RNA and 35% ribosomal proteins. Eukaryotic ribosomes are between 25 and 30 nm (250–300 Å) in diameter and the ratio of rRNA to protein is close to 1. Ribosomes translate messenger RNA (mRNA) and build polypeptide chains (e.g., proteins) using amino acids delivered by transfer RNA (tRNA). Their active sites are made of RNA, so ribosomes are now classified as "ribozymes".^[8]

Ribosomes build proteins from the genetic instructions held within messenger RNA. Free ribosomes are suspended in the cytosol (the semi-fluid portion of the cytoplasm); others are bound to the rough endoplasmic reticulum, giving it the appearance of roughness and thus its name, or to the nuclear envelope. As ribozymes are partly constituted from RNA, it is thought that they might be remnants of the RNA world.^[9] Although catalysis of the peptide bond involves the C2 hydroxyl of RNA's P-site (see Function section below) adenosine in a protein shuttle mechanism, other steps in protein synthesis (such as translocation) are caused by changes in protein conformations.

Ribosomes are sometimes referred to as organelles, but the use of the term organelle is often restricted to describing sub-cellular components that include a phospholipid membrane, which ribosomes, being entirely particulate, do not. For this reason, ribosomes may sometimes be described as "non-membranous organelles".

Ribosomes were first observed in the mid-1950s by Romanian cell biologist George Palade using an electron microscope as dense particles or granules^[10] for which he would win the Nobel Prize. The term "ribosome" was proposed by scientist Richard B. Roberts in 1958:

During the course of the symposium a semantic difficulty became apparent. To some of the participants, "microsomes" mean the ribonucleoprotein particles of the microsome fraction contaminated by other protein and lipid material; to others, the microsomes consist of protein and lipid contaminated by particles. The phrase “microsomal particles” does not seem adequate, and “ribonucleoprotein particles of the microsome fraction” is much too awkward. During the meeting, the word "ribosome" was suggested, which has a very satisfactory name and a pleasant sound. The present confusion would be eliminated if “ribosome” were adopted to designate ribonucleoprotein particles in sizes ranging from 35 to 100S.

— Roberts, R. B., Microsomal Particles and Protein Synthesis^[11]

The structure and function of the ribosomes and associated molecules, known as the translational apparatus, has been of research interest since the mid-twentieth century and is a very active field of study today.

Figure 2 : Large (red) and small (blue) subunit fit together

Ribosomes consist of two subunits (Figure 1) that fit together (Figure 2) and work as one to translate the mRNA into a polypeptide chain during protein synthesis (Figure 3). Bacterial subunits consist of one or two and eukaryotic of one or three very large RNA molecules (known as ribosomal RNA or rRNA) and multiple smaller protein molecules. Crystallographic work has shown that there are no ribosomal proteins close to the reaction site for polypeptide synthesis. This suggests that the protein components of ribosomes act as a scaffold that may enhance the ability of rRNA to synthesize protein rather than directly participating in catalysis (See: Ribozyme).

Biogenesis

Main article: Ribosome biogenesis

In bacterial cells, ribosomes are synthesized in the cytoplasm through the transcription of multiple ribosome gene operons. In eukaryotes, the process takes place both in the cell cytoplasm and in the nucleolus, which is a region within the cell nucleus. The assembly process involves the coordinated function of over 200 proteins in the synthesis and processing of the four rRNAs, as well as assembly of those rRNAs with the ribosomal proteins.

Ribosome locations

Ribosomes are classified as being either "free" or "membrane-bound".

A ribosome translating a protein that is secreted into the endoplasmic reticulum.

Free and membrane-bound ribosomes differ only in their spatial distribution; they are identical in structure. Whether the ribosome exists in a free or membrane-bound state depends on the presence of an ER-targeting signal sequence on the protein being synthesized, so an individual ribosome might be membrane-bound when it is making one protein, but free in the cytosol when it makes another protein.

Free ribosomes

Free ribosomes can move about anywhere in the cytosol, but are excluded from the cell nucleus and other organelles. Proteins that are formed from free ribosomes are released into the cytosol and used within the cell. Since the cytosol contains high concentrations of glutathione and is, therefore, a reducing environment, proteins containing disulfide bonds, which are formed from oxidized cysteine residues, cannot be produced in this compartment.

Membrane-bound ribosomes

When a ribosome begins to synthesize proteins that are needed in some organelles, the ribosome making this protein can become "membrane-bound". In eukaryotic cells this happens in a region of the endoplasmic reticulum (ER) called the "rough ER". The newly produced polypeptide chains are inserted directly into the ER by the ribosome undertaking vectorial synthesis and are then transported to their destinations, through the secretory pathway. Bound ribosomes usually produce proteins that are used within the plasma membrane or are expelled from the cell via exocytosis.^[12]

Structure

Atomic structure of the 30S Subunit from Thermus thermophilus. Proteins are shown in blue and the single RNA strand in orange. It is found by MRC Laboratory of Molecular Biology in Cambridge, England.^[13]

The ribosomal subunits of prokaryotes and eukaryotes are quite similar.^[14]

The unit of measurement is the Svedberg unit, a measure of the rate of sedimentation in centrifugation rather than size and accounts for why fragment names do not add up (70S is made of 50S and 30S).

Prokaryotes have 70S ribosomes, each consisting of a small (30S) and a large (50S) subunit. Their small subunit has a 16S RNA subunit (consisting of 1540 nucleotides) bound to 21 proteins. The large subunit is composed of a 5S RNA subunit (120 nucleotides), a 23S RNA subunit (2900 nucleotides) and 31 proteins.^[14] Affinity label for the tRNA binding sites on the E. coli ribosome allowed the identification of A and P site proteins most likely associated with the peptidyltransferase activity; labelled proteins are L27, L14, L15, L16, L2; at least L27 is located at the donor site, as shown by E. Collatz and A.P. Czernilofsky.^[15]^[16] Additional research has demonstrated that the S1 and S21 proteins, in association with the 3'-end of 16S ribosomal RNA, are involved in the initiation of translation.^[17]

Eukaryotes have 80S ribosomes, each consisting of a small (40S) and large (60S) subunit. Their 40S subunit has an 18S RNA (1900 nucleotides) and 33 proteins.^[18] The large subunit is composed of a 5S RNA (120 nucleotides), 28S RNA (4700 nucleotides), a 5.8S RNA (160 nucleotides) subunits and ~49 proteins.^[14]^[19] During 1977, Czernilofsky published research that used affinity labeling to identify tRNA-binding sites on rat liver ribosomes. Several proteins, including L32/33, L36, L21, L23, L28/29 and L13 were implicated as being at or near the peptidyl transferase center.^[20]

The ribosomes found in chloroplasts and mitochondria of eukaryotes also consist of large and small subunits bound together with proteins into one 70S particle.^[14] These organelles are believed to be descendants of bacteria (see Endosymbiotic theory) and as such their ribosomes are similar to those of bacteria.^[21]

The various ribosomes share a core structure, which is quite similar despite the large differences in size. Much of the RNA is highly organized into various tertiary structural motifs, for example pseudoknots that exhibit coaxial stacking. The extra RNA in the larger ribosomes is in several long continuous insertions, such that they form loops out of the core structure without disrupting or changing it.^[14] All of the catalytic activity of the ribosome is carried out by the RNA; the proteins reside on the surface and seem to stabilize the structure.^[14]

The differences between the bacterial and eukaryotic ribosomes are exploited by pharmaceutical chemists to create antibiotics that can destroy a bacterial infection without harming the cells of the infected person. Due to the differences in their structures, the bacterial 70S ribosomes are vulnerable to these antibiotics while the eukaryotic 80S ribosomes are not.^[22] Even though mitochondria possess ribosomes similar to the bacterial ones, mitochondria are not affected by these antibiotics because they are surrounded by a double membrane that does not easily admit these antibiotics into the organelle.^[23]

High-resolution structure

Atomic structure of the 50S Subunit from Haloarcula marismortui. Proteins are shown in blue and the two RNA strands in orange and yellow.^[24] The small patch of green in the center of the subunit is the active site.

The general molecular structure of the ribosome has been known since the early 1970s. In the early 2000s the structure has been achieved at high resolutions, on the order of a few Å.

The first papers giving the structure of the ribosome at atomic resolution were published in rapid succession in late 2000. First, the 50S (large prokaryotic) subunit from the archaeon Haloarcula marismortui was published.^[24] Soon after, the structure of the 30S subunit from Thermus thermophilus was published.^[13] Shortly thereafter, a more detailed structure was published.^[25] These structural studies were awarded the Nobel Prize in Chemistry in 2009. Early the next year (May 2001) these coordinates were used to reconstruct the entire T. thermophilus 70S particle at 5.5 Å resolution.^[26]

Two papers were published in November 2005 with structures of the Escherichia coli 70S ribosome. The structures of a vacant ribosome were determined at 3.5-Å resolution using x-ray crystallography.^[27] Then, two weeks later, a structure based on cryo-electron microscopy was published,^[28] which depicts the ribosome at 11–15 Å resolution in the act of passing a newly synthesized protein strand into the protein-conducting channel.

First atomic structures of the ribosome complexed with tRNA and mRNA molecules were solved by using X-ray crystallography by two groups independently, at 2.8 Å^[29] and at 3.7 Å.^[30] These structures allow one to see the details of interactions of the Thermus thermophilus ribosome with mRNA and with tRNAs bound at classical ribosomal sites. Interactions of the ribosome with long mRNAs containing Shine-Dalgarno sequences were visualized soon after that at 4.5- to 5.5-Å resolution.^[31]

More recently, in 2010 cryoelectron microscopy was used in determining the first complete atomic model of a eukaryotic 40S ribosomal structure in Tetrahymena thermophila. This research has revealed the structure of the 18S ribosomal RNA and all ribosomal proteins of the 40S subunit, as well as much about the 40S subunit's interaction with eIF1 during translation initiation.^[18] Similarly, in 2011 the eukaryotic 60S subunit structure was also determined from Tetrahymena thermophila in complex with eIF6.^[19]

Function

Main article: Translation (genetics)

Ribosomes are the workhorses of protein biosynthesis, the process of translating mRNA into protein. The mRNA comprises a series of codons that dictate to the ribosome the sequence of the amino acids needed to make the protein. Using the mRNA as a template, the ribosome traverses each codon (3 nucleotides) of the mRNA, pairing it with the appropriate amino acid provided by a tRNA. Molecules of transfer RNA (tRNA) contain a complementary anticodon on one end and the appropriate amino acid on the other. The small ribosomal subunit, typically bound to a tRNA containing the amino acid methionine, binds to an AUG codon on the mRNA and recruits the large ribosomal subunit. The ribosome then contains three RNA binding sites, designated A, P and E. The A site binds an aminoacyl-tRNA (a tRNA bound to an amino acid); the P site binds a peptidyl-tRNA (a tRNA bound to the peptide being synthesized); and the E site binds a free tRNA before it exits the ribosome. Protein synthesis begins at a start codon AUG near the 5' end of the mRNA. mRNA binds to the P site of the ribosome first. The ribosome is able to identify the start codon by use of the Shine-Dalgarno sequence of the mRNA in prokaryotes and Kozak box in eukaryotes.

Figure 3 : Translation of mRNA (1) by a ribosome (2)(shown as small and large subunits) into a polypeptide chain (3). The ribosome begins at the start codon of mRNA (AUG) and ends at the stop codon (UAG).

In Figure 3, both ribosomal subunits (small and large) assemble at the start codon (towards the 5' end of the mRNA). The ribosome uses tRNA that matches the current codon (triplet) on the mRNA to append an amino acid to the polypeptide chain. This is done for each triplet on the mRNA, while the ribosome moves towards the 3' end of the mRNA. Usually in bacterial cells, several ribosomes are working parallel on a single mRNA, forming what is called a polyribosome or polysome.

References

^ Korostelev AA (August 2011). "Structural aspects of translation termination on the ribosome". RNA (New York, N.Y.) 17 (8): 1409–21. doi:10.1261/rna.2733411. PMID 21700725. http://rnajournal.cshlp.org/cgi/pmidlookup?view=long&pmid=21700725.
^ Leavitt, Sarah A.; Marshall Nirenberg (June 2010). "Deciphering the Genetic Code: Marshall Nirenberg". Office of NIH History. http://history.nih.gov/exhibits/nirenberg/glossary.htm.
^ "Dog eat dogma". Genome Biol. 1 (2). 2000 July 28.. PMC 138841. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC138841/.
^ Benne R, Sloof P (1987). "Evolution of the mitochondrial protein synthetic machinery". BioSystems 21 (1): 51–68. doi:10.1016/0303-2647(87)90006-2. PMID 2446672.
^ "Ribosomes". http://www.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Ribosomes/Ribosome.HTML. Retrieved 2011-04-28.
^ Palade.
^ 2009 Nobel Prize in Chemistry, Nobel Foundation.
^ Rodnina MV, Beringer M, Wintermeyer W (2007). "How ribosomes make peptide bonds". Trends Biochem. Sci. 32 (1): 20–6. doi:10.1016/j.tibs.2006.11.007. PMID 17157507.
^ Cech T (2000). "Structural biology. The ribosome is a ribozyme". Science 289 (5481): 878–9. doi:10.1126/science.289.5481.878. PMID 10960319.
^ PALADE GE (January 1955). "A small particulate component of the cytoplasm". J Biophys Biochem Cytol 1 (1): 59–68. PMC 2223592. PMID 14381428. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2223592.
^ Roberts, R. B., editor. (1958) "Introduction" in Microsomal Particles and Protein Synthesis. New York: Pergamon Press, Inc.
^ http://www.ncbi.nlm.nih.gov/books/NBK26841/#A2204
^ ^a ^b Schluenzen F, Tocilj A, Zarivach R, Harms J, Gluehmann M, Janell D, Bashan A, Bartels H, Agmon I, Franceschi F, Yonath A (2000). "Structure of functionally activated small ribosomal subunit at 3.3 Å resolution". Cell 102 (5): 615–23. doi:10.1016/S0092-8674(00)00084-2. PMID 11007480.
^ ^a ^b ^c ^d ^e ^f The Molecular Biology of the Cell, fourth eddition. Bruce Alberts, et al. Garland Science (2002) pg. 342 ISBN 0-8153-3218-1
^ Czernilofsky, A; Collatz, E (1976). SITE OF REACTION ON RIBOSOMAL-PROTEIN L27 WITH AN AFFINITY LABEL DERIVATIVE OF TRANSFER-RNA-F(MET). 63. ELSEVIER SCIENCE BV. pp. 283–286. doi:10.1016/0014-5793(76)80112-3. http://www.ncbi.nlm.nih.gov/pubmed/770196. Retrieved January 2012.
^ Czernilofsky, A; Collatz, E (1974). "PROTEINS AT TRANSFER-RNA BINDING-SITES OF ESCHERICHIA-COLI RIBOSOMES". PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE United States OF AMERICA (NATL ACAD SCIENCES) 71 (1): 230–234. doi:10.1073/pnas.71.1.230. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC387971/. Retrieved January 2012.
^ Czernilofsky, A (1975). "30S RIBOSOMAL-PROTEINS ASSOCIATED WITH 3'-TERMINUS OF 16S RNA". FEBS LETTERS (ELSEVIER SCIENCE BV) 58 (1): 281–284. doi:10.1016/0014-5793(75)80279-1.
^ ^a ^b Rabl, Leibundgut, Ataide, Haag, Ban (February 2010). "Crystal Structure of the Eukaryotic 40S Ribosomal Subunit in Complex with Initiation Factor 1". Science 331 (6018): 730–736. doi:10.1126/science.1198308. http://www.sciencemag.org/content/331/6018/730.
^ ^a ^b Klinge, Voigts-Hoffmann, Leibundgut, Arpagaus, Ban (November 2011). "Crystal Structure of the Eukaryotic 60S Ribosomal Subunit in Complex with Initiation Factor 6". Science 334 (6058): 941–948. doi:10.1126/science.1211204.
^ Czernilofsky, A (1977). "IDENTIFICATION OF TRNA-BINDING SITES ON RAT-LIVER RIBOSOMES BY AFFINITY LABELING". Molecular and General Genetics (Springer Verlag) 153 (3): 231–235. doi:10.1007/BF00431588. http://www.springerlink.com/content/t090316k676700q1/. Retrieved January 2012.
^ The Molecular Biology of the Cell, fourth edition. Bruce Alberts, et al. Garland Science (2002) pg. 808 ISBN 0-8153-3218-1
^ Recht MI, Douthwaite S, Puglisi JD (1999). "Basis for bacterial specificity of action of aminoglycoside antibiotics". EMBO J 18 (11): 3133–8. doi:10.1093/emboj/18.11.3133. PMC 1171394. PMID 10357824. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1171394.
^ O'Brien, T.W., The General Occurrence of 55S Ribosomes in Mammalian Liver Mitochondria. J. Biol. Chem., 245:3409 (1971).
^ ^a ^b Ban N, Nissen P, Hansen J, Moore P, Steitz T (2000). "The complete atomic structure of the large ribosomal subunit at 2.4 Å resolution". Science 289 (5481): 905–20. doi:10.1126/science.289.5481.905. PMID 10937989.
^ Wimberly BT, Brodersen DE, Clemons WM, et al. (September 2000). "Structure of the 30S ribosomal subunit". Nature 407 (6802): 327–39. doi:10.1038/35030006. PMID 11014182.
^ Yusupov MM, Yusupova GZ, Baucom A, et al. (May 2001). "Crystal structure of the ribosome at 5.5 A resolution". Science 292 (5518): 883–96. doi:10.1126/science.1060089. PMID 11283358.
^ Schuwirth BS, Borovinskaya MA, Hau CW, et al. (November 2005). "Structures of the bacterial ribosome at 3.5 A resolution". Science 310 (5749): 827–34. doi:10.1126/science.1117230. PMID 16272117.
^ Mitra K, Schaffitzel C, Shaikh T, et al. (November 2005). "Structure of the E. coli protein-conducting channel bound to a translating ribosome". Nature 438 (7066): 318–24. doi:10.1038/nature04133. PMC 1351281. PMID 16292303. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1351281.
^ Selmer M, Dunham CM, Murphy FV, et al. (September 2006). "Structure of the 70S ribosome complexed with mRNA and tRNA". Science 313 (5795): 1935–42. doi:10.1126/science.1131127. PMID 16959973.
^ Korostelev A, Trakhanov S, Laurberg M, Noller HF (September 2006). "Crystal structure of a 70S ribosome-tRNA complex reveals functional interactions and rearrangements". Cell 126 (6): 1065–77. doi:10.1016/j.cell.2006.08.032. PMID 16962654.
^ Yusupova G, Jenner L, Rees B, Moras D, Yusupov M (November 2006). "Structural basis for messenger RNA movement on the ribosome". Nature 444 (7117): 391–4. doi:10.1038/nature05281. PMID 17051149.

External links

Wikimedia Commons has media related to: Ribosomes

70S Ribosome Architecture Animation of a working ribosome. Requires the Chime browser plugin from this site (where registration is required).
Lab computer simulates ribosome in motion
Role of the Ribosome, Gwen V. Childs, copied here
Ribosome in Proteopedia - The free, collaborative 3D encyclopedia of proteins & other molecules
Ribosomal proteins families in ExPASy

v d e Structures of the cell / organelles (TH H1.00.01.2-3)

Endomembrane system	Cell membrane · Nucleus (and Nucleolus) · Endoplasmic reticulum · Golgi apparatus · Parenthesome · Autophagosome Vesicles (Exosome · Lysosome · Endosome · Phagosome · Vacuole) Cytoplasmic granules: Melanosome · Microbody (Glyoxysome, Peroxisome) · Weibel–Palade body

Cytoskeleton	Microfilaments · Intermediate filaments · Microtubules · Prokaryotic cytoskeleton MTOCs: Centrosome/Centriole · Basal body · Spindle pole body Myofibril

Endosymbionts	Mitochondrion · Plastids (Chloroplast · Chromoplast · Leucoplast)

Other internal	RNA: Ribosome · Vault Cytoplasm · Proteasome

External	Undulipodium: Cilium/Flagellum · Axoneme · Radial spoke Cell wall · Acrosome

B strc: edmb (perx), skel (ctrs), epit, cili, mito, nucl (chro)

Ribosomal RNA / ribosome subunits

Prokaryotes (70S)

Large: 50S (5S, 23S)
Small: 30S (16S)

Eukaryotes (80S)

Cytoplasmic	Large: 60S (5S, 5.8S, 28S) Small: 40S (18S)

Mitochondrial	MT-RNR1, 12S · MT-RNR2, 16S

B bsyn: dna (repl, cycl, reco, repr) · tscr (fact, tcrg, nucl, rnat, rept, ptts) · tltn (risu, pttl, nexn) · dnab, rnab/runp · stru (domn, 1°, 2°, 3°, 4°)

This article incorporates public domain material from the NCBI document "Science Primer".

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

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ribosome

ri·bo·some

ribosome

Ribosome

ribosome

ribosome

ribosome

categories related to 'ribosome'

Ribosome

Description

Biogenesis

Ribosome locations

Free ribosomes

Membrane-bound ribosomes

Structure

High-resolution structure

Function

See also

References

External links

	What do ribosomes do? Read answer...
	What do ribosomes have on them? Read answer...
	What are ribosome and free ribosomes and what do they do in animal cells? Read answer...

	Which of this is ribosome?
	What are in ribosomes?
	What are ribosomes had of?