Ribosomal RNA - wikipedia Ribosomal RNA Three - dimensional views of the ribosome, showing rRNA in dark blue ( small subunit ) and dark red ( large subunit ). Lighter colors represent ribosomal proteins. Ribosomal ribonucleic acid ( rRNA ) is the RNA component of the ribosome, and is essential for protein synthesis in all living organisms. It constitutes the predominant material within the ribosome, which is approximately 60 % rRNA and 40 % protein by weight, or 3 / 5 of ribosome mass. Ribosomes contain two major rRNAs and 50 or more proteins. The ribosomal RNAs form two subunits, the large subunit ( LSU ) and small subunit ( SSU ). The LSU rRNA acts as a ribozyme, catalyzing peptide bond formation. rRNA sequences are widely used for working out evolutionary relationships among organisms, since they are of ancient origin and are found in all known forms of life. Contents 1 Structure 2 Subunits and ribosomal RNA genes 2.1 In prokaryotes 2.2 In eukaryotes 3 Transcription 3.1 In prokaryotes 3.2 In eukaryotes 4 Translation 5 Importance 6 Genes coding for ribosomal proteins 7 See also 8 References 9 External links Structure The ribosomal RNAs complex with proteins to form two subunits, the large subunit ( LSU ) and small subunit ( SSU ). During translation, mRNA is sandwiched between the small and large subunits, and the ribosome catalyzes the formation of a peptide bond between the two amino acids that are contained in the rRNA. A ribosome also has three 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 amino ( NH ) group of the aminoacyl - tRNA, which contains the new amino acid, attacks the ester linkage of peptidyl - tRNA ( contained within the P site ), which contains the last amino acid of the growing chain, forming a new peptide bond. This reaction is catalyzed by peptidyl transferase. The tRNA that was holding onto the last amino acid is moved to the E site, and what used to be the aminoacyl - tRNA is the peptidyl - tRNA. A single mRNA can be translated simultaneously by multiple ribosomes. Subunits and ribosomal RNA genes Both prokaryotic and eukaryotic ribosomes can be broken down into two subunits ( the S in 16S represents Svedberg units ), nt = length in nucleotides of the respective rRNAs, for exemplary species Escherichia coli ( prokaryote ) and human ( eukaryote ) : Type Size Large subunit ( LSU rRNA ) Small subunit ( SSU rRNA ) prokaryotic 70S 50S ( 5S : 120 nt, 23S : 2906 nt ) 30S ( 16S : 1542 nt ) eukaryotic 80S 60S ( 5S : 121 nt, 5.8 S : 156 nt, 28S : 5070 nt ) 40S ( 18S : 1869 nt ) Note that the S units of the subunits ( or the rRNAs ) can not 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. The nt units can be added as these represent the integer number of units in the linear rRNA polymers ( for example, the total length of the human rRNA = 7216 nt ). In prokaryotes In prokaryotes a small 30S ribosomal subunit contains the 16S ribosomal RNA. The large 50S ribosomal subunit contains two rRNA species ( the 5S and 23S ribosomal RNAs ). Bacterial 16S ribosomal RNA, 23S ribosomal RNA, and 5S rRNA genes are typically organized as a co-transcribed operon. There may be one or more copies of the operon dispersed in the genome ( for example, Escherichia coli has seven ). Archaea contains either a single rDNA operon or multiple copies of the operon. The 3 ' end of the 16S ribosomal RNA ( in a ribosome ) binds to a sequence on the 5 ' end of mRNA called the Shine - Dalgarno sequence. In eukaryotes Small subunit ribosomal RNA, 5 ' domain taken from the Rfam database. This example is RF00177 In contrast, eukaryotes generally have many copies of the rRNA genes organized in tandem repeats. In humans, approximately 300 -- 400 repeats are present in five clusters, located on chromosomes 13 ( RNR1 ), 14 ( RNR2 ), 15 ( RNR3 ), 21 ( RNR4 ) and 22 ( RNR5 ). Sequence variation in rRNA has been observed both within and between human individuals and certain variants are expressed in a tissue - specific manner in mice. Because of their special structure and transcription behaviour, rRNA gene clusters are commonly called `` ribosomal DNA '' ( note that the term seems to imply that ribosomes contain DNA, which is not the case ). The 18S rRNA in most eukaryotes is in the small ribosomal subunit, and the large subunit contains three rRNA species ( the 5S, 5.8 S and 28S in mammals, 25S in plants, rRNAs ). Mammalian cells have 2 mitochondrial ( 12S and 16S ) rRNA molecules and 4 types of cytoplasmic rRNA ( the 28S, 5.8 S, 18S, and 5S subunits ). The 28S, 5.8 S, and 18S rRNAs are encoded by a single transcription unit ( 45S ) separated by 2 internally transcribed spacers. The 45S rDNA is 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. 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. Transcription In prokaryotes In prokaryotic cells, each rRNA gene or operon is transcribed into a single RNA precursor that includes 16S, 23S, 5S rRNA and tRNA sequences along with transcribed spacers. The RNA processing then begins before the transcription is complete. During processing reactions, the rRNAs and tRNAs are released as separate molecules. In eukaryotes The genes coding for 18S, 28S and 5.8 S rRNA, located in the nucleolus organizer region, are transcribed into a large pre-rRNA molecule by RNA polymerase I. Each large pre-rRNA contains 18S, 28S and 5.8 S sequences which are separated by external and internal transcribed spacer sequences. During processing reactions, the 18S, 28S and 5.8 S rRNA are released as individual molecules. Processing reactions involve exo - and endo - nucleolytic cleavages guided by snoRNA ( small nucleolar RNAs ) in complex with proteins. The genes for 5S rRNA are located outside the nucleolus and are transcribed into pre-5S rRNA by RNA polymerase III. The pre-5S rRNA enters the nucleolus for processing and assembly with 28S and 5.8 S rRNA to form the large subunit. 18S rRNA forms the small ribosomal subunits by combining with ribosomal proteins. Translation 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 Shine -- Dalgarno sequence upstream of the start codon in mRNA. Importance Ribosomal RNA characteristics are important in evolution, thus taxonomy, and medicine. rRNA is one of only a few gene products present in all cells. For this reason, genes that encode the rRNA ( rDNA ) are sequenced to identify an organism 's taxonomic group, calculate related groups, and estimate rates of species divergence. As a result, many thousands of rRNA sequences are known and stored in specialized databases such as RDP - II and SILVA. rRNA is the target of numerous clinically relevant antibiotics : chloramphenicol, erythromycin, kasugamycin, micrococcin, paromomycin, ricin, alpha - sarcin, spectinomycin, streptomycin, and thiostrepton. rRNA have been shown to be the origin of species - specific microRNAs, like miR - 663 in humans and miR - 712 in mouse. These miRNAs originate from the internal transcribed spacers of the rRNA. Genes coding for ribosomal proteins These denote genes encoding for the proteins of the ribosome and are transcribed as mRNA, not rRNA. 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 See also Ribotyping Diazaborine, a maturation inhibitor of rRNAs for the large ribosomal subunit References Jump up ^ `` Homo sapiens 5S ribosomal RNA ''. Jump up ^ `` Homo sapiens 5.8 S ribosomal RNA ''. Jump up ^ `` Homo sapiens 28S ribosomal RNA ''. Jump up ^ `` Homo sapiens 18S ribosomal RNA ''. Jump up ^ Parks, MM ; Kurylo CM ; Dass RA ; Bojmar L ; Lyden D ; Vincent CT ; Blanchard SC ( 2018 ). `` Variant ribosomal RNA alleles are conserved and exhibit tissue - specific expression ''. Science Advances. 4 ( 2 ). doi : 10.1126 / sciadv. aao0665. Jump up ^ Yusupov MM, Yusupova GZ, Baucom A, et al. ( 2001 ). `` Crystal structure of the ribosome at 5.5 A resolution ''. Science. 292 ( 5518 ) : 883 -- 96. doi : 10.1126 / science. 1060089. PMID 11283358. Jump up ^ Wolfe, Stephen. Molecular and Cellular Biology. ISBN 978 - 0534124083. Jump up ^ `` rRNA synthesis and processing ''. Jump up ^ Wolfe, Stephen. Molecular and Cellular Biology. ISBN 978 - 0534124083. Jump up ^ Smit S, Widmann J, Knight R ( 2007 ). `` Evolutionary rates vary among rRNA structural elements ''. Nucleic Acids Res. 35 ( 10 ) : 3339 -- 54. doi : 10.1093 / nar / gkm101. PMC 1904297. PMID 17468501. Jump up ^ Meyer, Achim ; Todt, Christiane ; Mikkelsen, Nina T ; Lieb, Bernhard ( 2010 ). `` Fast evolving 18S rRNA sequences from Solenogastres ( Mollusca ) resist standard PCR amplification and give new insights into mollusk substitution rate heterogeneity ''. BMC Evolutionary Biology. 10 ( 1 ) : 70. doi : 10.1186 / 1471 - 2148 - 10 - 70. ISSN 1471 - 2148. Retrieved 27 July 2018. Jump up ^ Cole, JR ; Chai B ; Marsh TL ; Farris RJ ; Wang Q ; Kulam SA ; Chandra S ; McGarrell DM ; Schmidt TM ; Garrity GM ; Tiedje JM ( 2003 ). `` The Ribosomal Database Project ( RDP - II ) : previewing a new autoaligner that allows regular updates and the new prokaryotic taxonomy ''. Nucleic Acids Res. 31 ( 1 ) : 442 -- 3. doi : 10.1093 / nar / gkg039. PMC 165486. PMID 12520046. Jump up ^ Pruesse, E ; Quast C ; Knittel K ; Fuchs BM ; Ludwig W ; Peplies J ; Gloeckner FO ( 2007 ). `` SILVA : a comprehensive online resource for quality checked and aligned ribosomal RNA sequence data compatible with ARB ''. Nucleic Acids Res. 35 ( 1 ) : 7188 -- 7196. doi : 10.1093 / nar / gkm864. PMC 2175337. PMID 17947321. Jump up ^ The atypical mechanosensitive microRNA - 712 derived from pre-ribosomal RNA induces endothelial inflammation and atherosclerosis Nature Communications, 2013 doi : 10.1038 / ncomms4000 External links SILVA rRNA Database Project ( also includes Eukaryotes ( 18S ) and LSU ( 23S / 28S ) ) Ribosomal Database Project II 16S rRNA, BioMineWiki Ribosomal + RNA at the US National Library of Medicine Medical Subject Headings ( MeSH ) Types of nucleic acids Constituents Nucleobases Nucleosides Nucleotides Deoxynucleotides Ribonucleic acids ( coding, non-coding ) Translational Messenger precursor, heterogenous nuclear Transfer Ribosomal Transfer - messenger Regulatory Interferential Micro Small interfering Piwi - interacting Antisense Processual Small nuclear Small nucleolar Small Cajal Body RNAs Y RNA Enhancer RNAs Others Guide Ribozyme Small hairpin Small temporal Trans - acting small interfering Subgenomic messenger Deoxyribonucleic acids Complementary Chloroplast Deoxyribozyme Genomic Multicopy single - stranded Mitochondrial Analogues Xeno Glycol Threose Hexose Locked Peptide Morpholino Cloning vectors Phagemid Plasmid Lambda phage Cosmid Fosmid Artificial chromosomes P1 - derived Bacterial Yeast Human Protein biosynthesis : translation ( bacterial, archaeal, eukaryotic ) Proteins Initiation factor Bacterial PIF - 1 PIF - 2 PIF - 3 Archaeal aIF1 aIF2 aIF5 aIF6 Eukaryotic eIF1 eIF1 EIF1AX AY 1B eIF2 EIF2S1 EIF2S2 EIF2S3 EIF2B1 EIF2B2 EIF2B3 EIF2B4 EIF2B5 EIF - 2 kinase eIF2A eIF2D eIF3 EIF3A eIF4 EIF4A2 A3 E1 E2 E3 G1 G2 G3 eIF5 EIF5 EIF5A A2 5B eIF6 EIF6 Elongation factor Bacterial EF - Tu EF - Ts EF - G Archaeal aEF - 1 aEF - 2 Eukaryotic EEF - 1 EEF1A1 EEF1A2 EEF1A3 EEF1B1 EEF1B2 EEF1B3 EEF1B4 EEF1D EEF1E1 EEF1G EEF2 Release factor Bacterial Archaeal Eukaryotic ( ETF1 ) Ribosomal Proteins Cytoplasmic 60S subunit RPL3 RPL4 RPL5 RPL6 RPL7 RPL7A RPL8 RPL9 RPL10 RPL10A RPL10 - like RPL11 RPL12 RPL13 RPL13A RPL14 RPL15 RPL17 RPL18 RPL18A RPL19 RPL21 RPL22 RPL23 RPL23A RPL24 RPL26 RPL27 RPL27A RPL28 RPL29 RPL30 RPL31 RPL32 RPL34 RPL35 RPL35A RPL36 RPL36A RPL37 RPL37A RPL38 RPL39 RPL40 RPL41 RPLP0 RPLP1 RPLP2 RRP15 - like RSL24D1 40S subunit RPSA RPS2 RPS3 RPS3A RPS4 ( RPS4X, RPS4Y1, RPS4Y2 ) RPS5 RPS6 RPS7 RPS8 RPS9 RPS10 RPS11 RPS12 RPS13 RPS14 RPS15 RPS15A RPS16 RPS17 RPS18 RPS19 RPS20 RPS21 RPS23 RPS24 RPS25 RPS26 RPS27 RPS27A RPS28 RPS29 RPS30 RACK1 Mitochondrial 39S subunit MRPL1 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 28S subunit MRPS1 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 Other concepts Aminoacyl tRNA synthetase Reading frame Start codon Stop codon Shine - Dalgarno sequence / Kozak consensus sequence Ribosomal RNA / ribosome subunits Archaea Large : Small : Bacteria ( 70 S ) Large : 50S 5S 23S Small : 30S 16S Eukaryotes ( 80 S ) Cytoplasmic Large : 60S 5S 5.8 S 28S Small : 40S 18S Mitochondrial Large : MT - RNR2, 16S Small : MT - RNR1, 12S Chloroplast Large chloroplast subunit Small chloroplast subunit Retrieved from `` https://en.wikipedia.org/w/index.php?title=Ribosomal_RNA&oldid=856785863 '' Categories : Protein biosynthesis RNA Non-coding RNA Ribosomal RNA Ribozymes Talk Contents About Wikipedia Български Bosanski Brezhoneg Català Čeština Dansk Deutsch Eesti Ελληνικά Español Esperanto فارسی Français Galego 한국어 Հայերեն Hrvatski Bahasa Indonesia Italiano עברית ქართული Кыргызча Lietuvių Magyar Македонски Nederlands 日本 語 Occitan Polski Português Română Русский Scots Simple English Slovenčina کوردی Suomi Svenska Tagalog ไทย Türkçe Українська Tiếng Việt 中文 36 more Edit links This page was last edited on 27 August 2018, at 14 : 35 ( UTC ). 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Question: where is ribosomal rna found in the cell
Answer: the ribosome