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| Ribosomes are fictional people that live in your body having intercourse. | |||
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| ] cell, showing subcellular components including ribosomes'' (3).<br/> | |||
| ]s:<br/> | |||
| (1) ]<br/> | |||
| (2) ]<br/> | |||
| '''(3) ribosomes''' (little dots)<br/> | |||
| (4) ]<br/> | |||
| (5) rough ] (ER)<br/> | |||
| (6) ]<br/> | |||
| (7) ]<br/> | |||
| (8) smooth ER<br/> | |||
| (9) ]<br/> | |||
| (10) ]<br/> | |||
| (11) ]<br/> | |||
| (12) ]<br/> | |||
| (13) ]s within ]]] | |||
| '''Ribosomes''' (''from '''ribo'''nucleic acid and "Greek: '''soma''' (''meaning'' body)"'') are complexes of ] and ] that are found in all ]s. The ribosome is part of the mechanism that translates the ] sequence into the protein sequence. Ribosomes from ], ] and ]s (the three domains of ]), have significantly different structure and RNA. The ribosomes in the ] of eukaryotic cells resemble those in bacteria, reflecting the evolutionary origin of this ].<ref>{{cite journal |author=Benne R, Sloof P |title=Evolution of the mitochondrial protein synthetic machinery |journal=BioSystems |volume=21 |issue=1 |pages=51–68 |year=1987 |pmid=2446672 |doi=10.1016/0303-2647(87)90006-2}}</ref> | |||
| The ribosome is part of the mechanism that ] the genetic code from nucleic acid into ] chains. Ribosomes assemble individual ]s into ] chains. Ribosomes bind to a ] molecule, which they use as a template to join the correct sequence of amino acids. The amino acids are attached to ] molecules, which read the messenger RNA sequence and attach the proteins in the correct sequence. | |||
| ==Description== | |||
| '''Ribosomes''' are about 20 ] (200 ]s) in diameter and are composed of 65% ] and 35% ]s (known as a ] or RNP){{Citation needed|there are archeal, eubacterial and eukaryotic ribosomes; they should defer in composition and in %'s of protein and RNA|date=October 2009}}. They ] ] to build ] chains (e.g., ]s) using amino acids delivered by ]. Their active sites are made of RNA, so ribosomes are now classified as "]s".<ref>{{cite journal |author=Rodnina MV, Beringer M, Wintermeyer W |title=How ribosomes make peptide bonds |journal=Trends Biochem. Sci. |volume=32 |issue=1 |pages=20–6 |year=2007 |pmid=17157507 |doi=10.1016/j.tibs.2006.11.007}}</ref> | |||
| Ribosomes build proteins from the genetic instructions held within ]. Free ribosomes are suspended in the ] (the semi-fluid portion of the ]); others are bound to the ], giving it the appearance of roughness and thus its name, or to the ]. As ribozymes are partly constituted from RNA, it is thought that they might be remnants of the ].<ref>{{cite journal |author=Cech T |title=Structural biology. The ribosome is a ribozyme |journal=Science |volume=289 |issue=5481 |pages=878–9 |year=2000 |pmid=10960319 | doi = 10.1126/science.289.5481.878 <!--Retrieved from CrossRef by DOI bot-->}}</ref> Although catalysis of the ] involves the C2 hydroxyl of RNA's P-site 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 ]s, 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 ]n cell biologist ] using an ] as dense particles or granules<ref>G.E. Palade. (1955) "A small particulate component of the cytoplasm". ''J Biophys Biochem Cytol.'' Jan;1(1): pages 59-68. PMID 14381428</ref> for which he would win the ]. The term "ribosome" was proposed by scientist Richard B. Roberts in 1958: | |||
| {{Quotation|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; this seems a very satisfactory name, and it has 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<ref>Roberts, R. B., editor. (1958) "Introduction" in ''Microsomal Particles and Protein Synthesis.'' New York: Pergamon Press, Inc.</ref>}} | |||
| 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. | |||
| ] | |||
| 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). ] subunits consist of one or two and eukaryotic of one or three very large ] molecules (known as ] or rRNA) and multiple smaller protein molecules. ] 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: ]). | |||
| ==Biogenesis== | |||
| {{Main|Ribosome biogenesis}} | |||
| In bacterial cells, ribosomes are synthesized in the cytoplasm through the ] of multiple ribosome gene ]s. In eukaryotes, the process takes place both in the cell cytoplasm and in the nucleolus, which is a region within the ]. 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". | |||
| Free and membrane-bound ribosomes differ only in their spatial distribution; they are identical in structure and function. Whether the ribosome exists in a free or membrane-bound state depends on the presence of an ] on the protein being synthesized. | |||
| ===Free ribosomes=== | |||
| Free ribosomes are free to move about anywhere in the ]. Proteins that are formed from free ribosomes are used within the cell. Proteins containing ] using ] ] cannot be produced outside of the ] of the endoplasmic reticulum. | |||
| ===Membrane-bound ribosomes=== | |||
| When certain proteins are synthesized 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 and are then transported to their destinations. Bound ribosomes usually produce proteins that are used within the cell membrane or are expelled from the cell via '']''. | |||
| ==Structure== | |||
| ]''. Proteins are shown in blue and the single RNA strand in orange.<ref name=Schluenzen>{{cite journal |author=Schluenzen F, Tocilj A, Zarivach R, Harms J, Gluehmann M, Janell D, Bashan A, Bartels H, Agmon I, Franceschi F, Yonath A |title=Structure of functionally activated small ribosomal subunit at 3.3 angstroms resolution |journal=Cell |volume=102 |issue=5 |pages=615–23 |year=2000 |pmid=11007480 | doi = 10.1016/S0092-8674(00)00084-2 <!--Retrieved from CrossRef by DOI bot-->}}</ref>]] | |||
| The ribosomal subunits of ]s and eukaryotes are quite similar.<ref name = alberts> The Molecular Biology of the Cell, fourth eddition. Bruce Alberts, et al. Garland Science (2002) pg. 342 ISBN 0-8153-3218-1</ref> | |||
| The unit of measurement is the ] unit, a measure of the rate of ] in ] rather than size and accounts for why fragment names do not add up (70S is made of 50S and 30S). | |||
| Prokaryotes have 70] ribosomes, each consisting of a small (]) and a large (]) subunit. Their large subunit is composed of a ] ] subunit (consisting of 120 nucleotides), a 23S RNA subunit (2900 nucleotides) and 34 ]s. The 30S subunit has a 1540 nucleotide RNA subunit (]) bound to 21 proteins.<ref name = alberts/> | |||
| Eukaryotes have 80S ribosomes, each consisting of a small (]) and large (]) subunit. Their large subunit is composed of a 5S RNA (120 nucleotides), a 28S RNA (4700 nucleotides), a 5.8S subunit (160 nucleotides) and ~49 proteins. The 40S subunit has a 1900 nucleotide (18S) RNA and ~33 proteins.<ref name = alberts/> | |||
| The ribosomes found in ]s and ] of eukaryotes also consist of large and small subunits bound together with ]s into one 70S particle.<ref name = alberts/> These ] are believed to be descendants of ] (see ]) and as such their ribosomes are similar to those of bacteria.<ref> The Molecular Biology of the Cell, fourth edition. Bruce Alberts, et al. Garland Science (2002) pg. 808 ISBN 0-8153-3218-1</ref> | |||
| The various ribosomes share a core structure, which is quite similar despite the large differences in size. The extra ] 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.<ref name = alberts> The Molecular Biology of the Cell, fourth edition. Brusce Alberts, et al. Garland Science (2002) pg. 342 ISBN 0-8153-3218-1</ref> All of the catalytic activity of the ribosome is carried out by the ]; the proteins reside on the surface and seem to stabilize the structure.<ref name = alberts/> | |||
| The differences between the bacterial and eukaryotic ribosomes are exploited by ] to create ]s 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.<ref name=Recht>{{cite journal |author=Recht MI, Douthwaite S, Puglisi JD |title=Basis for bacterial specificity of action of aminoglycoside antibiotics |journal=EMBO J |volume=18 |issue=11 |pages=3133–8 |year=1999 |pmid=10357824 | doi = 10.1093/emboj/18.11.3133 <!--Retrieved from CrossRef by DOI bot-->}}</ref> Even though ] 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 ].<ref> O'Brien, T.W., The General Occurrence of 55S Ribosomes in Mammalian Liver Mitochondria. J. Biol. Chem., 245:3409 (1971).</ref> | |||
| ===High-resolution structure=== | |||
| ]''. Proteins are shown in blue and the two RNA strands in orange and yellow.<ref name=Ban>{{cite journal |author=Ban N, Nissen P, Hansen J, Moore P, Steitz T |title=The complete atomic structure of the large ribosomal subunit at 2.4 ångström resolution |journal=Science |volume=289 |issue=5481 |pages=905–20 |year=2000 |pmid=10937989 | doi = 10.1126/science.289.5481.905 <!--Retrieved from CrossRef by DOI bot-->}}</ref> 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 ångströms. | |||
| The first papers giving the structure of the ribosome at atomic resolution were published in rapid succession in late 2000. First, the 50S (large bacteria) subunit from the ], ''Haloarcula marismortui'' was published.<ref name=Ban/> Soon after the structure of the 30S subunit from '']'' was published.<ref name="Schluenzen"/> Shortly thereafter a more detailed structure was published.<ref>Wimberly BT, Brodersen DE, Clemons WM Jr, Morgan-Warren RJ, Carter AP, Vonrhein C, Hartsch T, Ramakrishnan V. Structure of the 30S ribosomal subunit. ''Nature.'' 2000 Sep 21;407(6802):327-39. PMID 11014182</ref> 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 '']'' 70S particle at 5.5 ångström resolution.<ref>Yusupov MM, Yusupova GZ, Baucom A, Lieberman K, Earnest TN, Cate JH, Noller HF. Crystal structure of the ribosome at 5.5 ångström resolution. ''Science.'' 2001 May 4;292(5518):883-96. Epub 2001 Mar 29. PMID 11283358</ref> | |||
| Two papers were published in November 2005 with structures of the '']'' 70S ribosome. The structures of vacant ribosome were determined at 3.5-ångström resolution using ].<ref>Schuwirth BS, Borovinskaya MA, Hau CW, Zhang W, Vila-Sanjurjo A, Holton JM, Cate JH. Structures of the bacterial ribosome at 3.5 ångström resolution. ''Science.'' 2005 Nov 4;310(5749):827-34. PMID 16272117</ref> Then, two weeks later, a structure based on cryo-] was published,<ref>Mitra K, Schaffitzel C, Shaikh T, Tama F, Jenni S, Brooks CL 3rd, Ban N, Frank J. Structure of the ''E. coli'' protein-conducting channel bound to a translating ribosome. ''Nature.'' 2005 Nov 17;438(7066):318-24. PMID 16292303</ref> which depicts the ribosome at 11-15 ångström resolution in the act of passing a newly synthesized protein strand into the protein-conducting channel. | |||
| First atomic structures of the ribosome complexed with ] and ] molecules were solved by using X-ray crystallography by two groups independently, at 2.8 ångström<ref>Selmer, M., Dunham, C.M., Murphy, F.V IV, Weixlbaumer, A., Petry S., Kelley, A.C., Weir, J.R. and Ramakrishnan, V. (2006). Structure of the 70S ribosome complexed with mRNA and tRNA. Science , 313, 1935-1942. PMID 16959973</ref> and at 3.7 ångström.<ref> Korostelev A, Trakhanov S, Laurberg M, Noller HF. Crystal structure of a 70S ribosome-tRNA complex reveals functional interactions and rearrangements. Cell. 2006 Sep 22;126(6):1065-77</ref> These structures allow one to see the details of interactions of the '']'' ribosome with ] and with ]s bound at classical ribosomal sites. Interactions of the ribosome with long mRNAs containing ]s were visualized soon after that at 4.5- to 5.5-ångström resolution.<ref>Yusupova G, Jenner L, Rees B, Moras D, Yusupov M. Structural basis for messenger RNA movement on the ribosome. Nature. 2006 Nov 16;444(7117):391-4</ref> | |||
| ==Function== | |||
| {{Main|Translation (biology)}} | |||
| Ribosomes are the workhorses of ], the process of translating mRNA into ]. The mRNA comprises a series of ]s that dictate to the ribosome the sequence of the ]s 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 ] (tRNA) contain a complementary ] on one end and the appropriate amino acid on the other. The small ribosomal subunit, typically bound to a tRNA containing the amino acid ], 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 ] 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. | |||
| ] | |||
| In Figure 3, both ribosomal subunits (<font color="#0000AA">small</font> and <font color="#AA0000">large</font>) assemble at the start codon (towards the 5' end of the mRNA). The ribosome uses ] that matches the current codon (triplet) on the mRNA to append an ] 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 '']''. | |||
| ==Nobel Prize== | |||
| The ] in ] 2009 was awarded to Drs ], ] and ] "for studies of the structure and function of the ribosome"<ref>, Nobel Foundation.</ref> | |||
| ==See also== | |||
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| *]s | |||
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| ==References== | |||
| {{reflist|2}} | |||
| ==External links== | |||
| * . Requires the Chime browser plugin from (where registration is required). | |||
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| * , Gwen V. Childs, copied | |||
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| {{Ribosome subunits}} | |||
| {{NCBI-scienceprimer}} | |||
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Revision as of 16:39, 15 October 2009
Ribosomes are fictional people that live in your body having intercourse.