- Ribosomal RNA
Ribosomal RNA (rRNA) is the central component of the
ribosome, the protein manufacturing machinery of all living cells. The function of the rRNA is to provide a mechanism for decoding mRNAinto amino acids and to interact with the tRNAs during translation by providing peptidyl transferaseactivity.
Inside the ribosome
The ribosome is composed of two subunits, named for how rapidly they sediment when subject to
centrifugation. tRNA is sandwiched between the small and large subunits and the ribosome catalyzes the formation of a peptide bond between the 2 amino acids that are contained in the tRNA.
The ribosome also has 3 binding sites called A, P, and E.
* The A site in the ribosome binds to an aminoacyl-tRNA (a tRNA bound to an amino acid).
* The NH2 group of the aminoacyl-tRNA which contains the new amino acid, attacks the carboxyl group of peptidyl-tRNA (contained within the P site) which contains the last amino acid of the growing chain called
peptidyl transferase reaction.
* The tRNA that was holding on the last amino acid is moved to the E site, and what used to be the aminoacyl-tRNA is now the peptidyl-tRNA.
A single mRNA can be translated simultaneously by multiple ribosomes.
Prokaryotes vs. Eukaryotes
prokaryoticand eukaryoticcan be broken down into two subunits (the S in 16S represents Svedbergunits):
Note that the S units of the subunits cannot simply be added because they represent measures of sedimentation rate rather than of mass. The sedimentation rate of each subunit is affected by its shape, as well as by its mass.
prokaryotesa small 30S ribosomal subunit contains the 16S rRNA.
The large 50S ribosomal subunit contains two rRNA species (the 5S and 23S rRNAs).
There may be one or more copies of the
operondispersed in the genome(for example, " Escherichia coli" has seven). Archaeacontains either a single rDNA operonor multiple copies of the operon.
The 3' end of the 16S rRNA (in a ribosome) binds to a sequence on the 5' end of mRNA called the
eukaryotesgenerally have many copies of the rRNA genes organized in tandem repeats; in humans approximately 300–400 rDNA repeats are present in five clusters (on chromosomes13, 14, 15, 21 and 22).
Mammalian cells have 2 mitochondrial (12S and 16S) rRNA molecules and 4 types of cytoplasmic rRNA (28S, 5.8S, 5S (large ribosome subunit) and 18S (small subunit). 28S, 5.8S, and 18S rRNAs are encoded by a single transcription unit (45S) separated by 2 Internally transcribed spacer (ITS). The 45S rDNA organized into 5 clusters (each has 30-40 repeats) on chromosomes 13, 14, 15, 21, and 22. These are transcribed by
RNA polymerase I. 5S occurs in tandem arrays (~200-300 true 5S genes and many dispersed pseudogenes), the largest one on the chromosome 1q41-42. 5S rRNA is transcribed by RNA polymerase III.
The tertiary structure of the small subunit ribosomal RNA (SSU rRNA) has been resolved by X-ray crystallography cite journal | author = Yusupov MM, Yusupova GZ, Baucom A, "et al" | title = Crystal structure of the ribosome at 5.5 A resolution | journal = Science | volume = 292 | issue = 5518 | pages = 883–96 | year = 2001 | pmid = 11283358 | doi = 10.1126/science.1060089 ] . The secondary structure of SSU rRNA contains 4 distinct domains — the 5', central, 3' major and 3' minor domains. A model of the secondary structure for the 5' domain (500-800 nucleotides) is shown.
Translation is the net effect of proteins being synthesized by ribosomes, from a copy (mRNA) of the DNA template in the nucleus. One of the components of the ribosome (16s rRNA) base pairs complementary to a sequence upstream of the
start codonin mRNA.
Importance of rRNA
Ribosomal RNA characteristics are important in
medicineand in evolution.
* rRNA is the target of several clinically relevant
antibiotics: chloramphenicol, erythromycin, kasugamycin, micrococcin, paromomycin, ricin, sarcin, spectinomycin, streptomycin, and thiostrepton.
* rRNA is the most conserved (least variable) gene in all cells.cite journal |author=Smit S, Widmann J, Knight R |title=Evolutionary rates vary among rRNA structural elements |journal=Nucleic Acids Res |volume=35 |issue=10 |pages=3339–3354 |year=2007 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1904297 |doi=10.1093/nar/gkm101 |pmid=17468501] For this reason, genes that encode the rRNA (rDNA) are sequenced to identify an organism's
taxonomicgroup, calculate related groups, and estimate rates of species divergence. For this reason many thousands of rRNA sequences are known and stored in specialized databases such as RDP-II [cite journal | last = Cole | first = JR | coauthors = Chai B, Marsh TL, Farris RJ, Wang Q, Kulam SA, Chandra S, McGarrell DM, Schmidt TM, Garrity GM, Tiedje JM | year = 2003 | title = The Ribosomal Database Project (RDP-II): previewing a new autoaligner that allows regular updates and the new prokaryotic taxonomy | journal = Nucleic Acids Res | volume = 31 | pages = 442–443 | pmid = 12520046 | doi = 10.1093/nar/gkg039] and the European SSU database. [cite journal | last = Wuyts | first = J | coauthors = Van de Peer Y, Winkelmans T, De Wachter R | year = 2002 | title = The European database on small subunit ribosomal RNA | journal = Nucleic Acids Res | volume = 30 | pages = 183–185 | pmid = 11752288 | doi = 10.1093/nar/30.1.183]
RPL1, RPL2, RPL3, RPL4, RPL5, RPL6, RPL7, RPL8, RPL9, RPL10, RPL11, RPL12, RPL13, RPL14, RPL15, RPL16, RPL17, RPL18, RPL19, RPL20, RPL21, RPL22, RPL23, RPL24, RPL25, RPL26, RPL27, RPL28, RPL29, RPL30, RPL31, RPL32, RPL33, RPL34, RPL35, RPL36, RPL37, RPL38, RPL39, RPL40, RPL41
MRPL1, MRPL2, MRPL3, MRPL4, MRPL5, MRPL6, MRPL7, MRPL8, MRPL9, MRPL10, MRPL11, MRPL12, MRPL13, MRPL14, MRPL15, MRPL16, MRPL17, MRPL18, MRPL19, MRPL20, MRPL21, MRPL22, MRPL23, MRPL24, MRPL25, MRPL26, MRPL27, MRPL28, MRPL29, MRPL30, MRPL31, MRPL32, MRPL33, MRPL34, MRPL35, MRPL36, MRPL37, MRPL38, MRPL39, MRPL40, MRPL41, MRPL42
RPS1, RPS2, RPS3, RPS4, RPS5, RPS6, RPS7, RPS8, RPS9, RPS10, RPS11, RPS12, RPS13, RPS14, RPS15, RPS16, RPS17, RPS18, RPS19, RPS20, RPS21, RPS22, RPS23, RPS24, RPS25, RPS26, RPS27, RPS28, RPS29
MRPS1, MRPS2, MRPS3, MRPS4, MRPS5, MRPS6, MRPS7, MRPS8, MRPS9, MRPS10, MRPS11, MRPS12, MRPS13, MRPS14, MRPS15, MRPS16, MRPS17, MRPS18, MRPS19, MRPS20, MRPS21, MRPS22, MRPS23, MRPS24, MRPS25, MRPS26, MRPS27, MRPS28, MRPS29, MRPS30, MRPS31, MRPS32, MRPS33, MRPS34, MRPS35
* [http://www.his.se/upload/21749/Ribosomal%20RNA.pdf "Ribosomal RNA"] by Denis LJ Lafontaine and David Tollervey
* [http://www.arb-silva.de SILVA rRNA Database Project] (also includes Eukaryotes (18S) and LSU (23S/28S))
* [http://www.psb.ugent.be/rRNA/ European database on small subunit ribosomal RNA]
* [http://rdp.cme.msu.edu/ Ribosomal Database Project II]
* [http://wiki.biomine.skelleftea.se/wiki/index.php/16S_ribosomal_RNA 16S rRNA, BioMineWiki]
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Look at other dictionaries:
ribosomal RNA — n. a form of RNA that is one of the constituent elements of ribosomes and is associated with messenger RNA and transfer RNA in the synthesis of proteins … English World dictionary
ribosomal RNA — ribosomal RNA. См. рРНК. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) … Молекулярная биология и генетика. Толковый словарь.
Ribosomal RNA — A molecular component of a ribosome, the cell s essential protein factory. Ribosomal RNA (rRNA) fabricates polypeptides (assemblies of amino acids that make up proteins). A tiny particulate structure located in the cytoplasm of the cell (outside… … Medical dictionary
ribosomal RNA — noun : RNA that is a fundamental structural element of the ribosome * * * Biochem. a type of RNA, distinguished by its length and abundance, functioning in protein synthesis as a component of ribosomes. Abbr.: rRNA [1960 65; RIBOSOME + AL1] * * * … Useful english dictionary
ribosomal RNA — ribosominė RNR statusas T sritis chemija apibrėžtis Ribonukleorūgštis, kuri susijungusi su baltymu sudaro ribosomą. santrumpa( os) rRNR atitikmenys: angl. ribosomal RNA rus. рибосомная РНК … Chemijos terminų aiškinamasis žodynas
ribosomal RNA — Abbreviation: rRNA The RNA molecules that are essential structural and functional components of ribosomes, where protein synthesis occurs. Different classes of rRNA molecule are identified by their sedimentation (S) values. E. coli ribosomes… … Glossary of Biotechnology
ribosomal RNA — noun Date: 1961 RNA that is a fundamental structural element of ribosomes called also rRNA … New Collegiate Dictionary
ribosomal RNA — (rRNA) The RNA present in ribosomes; ribosomes contain several sizes of single stranded rRNA that contribute to ribosome structure and are also directly involved in the mechanism of protein synthesis … Dictionary of microbiology
ribosomal RNA — See RNA … Dictionary of molecular biology
ribosomal RNA — Biochem. a type of RNA, distinguished by its length and abundance, functioning in protein synthesis as a component of ribosomes. Abbr.: rRNA [1960 65; RIBOSOME + AL1] * * * … Universalium