Transfer RNA (tRNA): Difference between revisions

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<StructureSection load='' size='350' side='right' scene='43/433638/Fullview_cartoon/8' caption='Phenylalanine-tRNA from yeast (PDB code [[1ehz]])'>[[Image:TRNA phe yeast.png|left|thumb|Standard 2D cloverleaf structure of tRNA. The shown example is phenylalanine-specific tRNA from yeast]]
<StructureSection load='' size='350' side='right' scene='43/433638/Fullview_cartoon/8' caption='Phenylalanine-tRNA from yeast (PDB code [[1ehz]])'>[[Image:TRNA phe yeast.png|left|thumb|Standard 2D cloverleaf structure of tRNA. The shown example is phenylalanine-specific tRNA from yeast]]
==Structure==
==Structure==
tRNA is a stable, folded kind of RNA present in all living cells. The secondary structure of most tRNA<ref>PMID:4601792</ref><ref>PMID:4612535</ref> is composed of four helical stems (shown in cyan, blue, red and yellow) arranged in a cloverleaf structure ) and an central four-way junction. <scene name='43/433638/Wireframe/1'>In three dimensions</scene>, tRNA adopts an "L" shape, with the <jmol>
tRNA is a stable, folded type of RNA present in all living cells. The secondary structure of most tRNA<ref>PMID:4601792</ref><ref>PMID:4612535</ref> is composed of four helical stems (shown in cyan, blue, red and yellow) arranged in a cloverleaf structure and an central four-way junction. <scene name='43/433638/Wireframe/1'>In three dimensions</scene>, tRNA adopts an "L" shape, with the <jmol>
<jmolLink>
<jmolLink>
<script> select 73-76; spacefill on; delay 0.5; spacefill off;
<script> select 73-76; spacefill on; delay 0.5; spacefill off;
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In addition, tRNA have a variable loop located in between the acceptor and D-stems. This variable loop can be quite small, but for some tRNA such as the serine or leucine-specific tRNA, it can form an additional helix.  
In addition, tRNA have a variable loop located in between the acceptor and D-stems. This variable loop can be quite small, but for some tRNA such as the serine or leucine-specific tRNA, it can form an additional helix.  


'''Modified nucleotides.''' Most tRNAs contain modified nucleotides[2], which are added post-transcriptionally by specific enzymes. Common modifications include isomerisation of uridines into pseudouridines (Ψ), methylation of either the ribose and/or the base, thiolation, reduction of uridines into dihydrouridines (D). The anticodon loop of the tRNA quite often contains hypermodified bases, the function of which is to stabilize the codon-anticodon interaction within the ribosome. The nature and position of nucleotide modifications is both specific of the organism and the tRNA type. Common modified nucleotides include :  
'''Modified nucleotides.''' Most tRNAs contain modified nucleotides<ref>PMID:20459084</ref>, which are added post-transcriptionally by specific enzymes. Common modifications include isomerisation of uridines into pseudouridines (Ψ), methylation of either the ribose and/or the base, thiolation, reduction of uridines into dihydrouridines (D). The anticodon loop of the tRNA quite often contains hypermodified bases, the function of which is to stabilize the codon-anticodon interaction within the ribosome. The nature and position of nucleotide modifications is both specific of the organism and the tRNA type. Common modified nucleotides include:  
* 5-methyluridine (ribothymidine) at position 54  
* 5-methyluridine (ribothymidine) at position 54  
* <scene name='43/433638/Pseudouridine/1'>pseudouridine at position 55</scene>  
* <scene name='43/433638/Pseudouridine/1'>pseudouridine at position 55</scene>  
* dihydrouridine(s) in the D-loop  
* dihydrouridine(s) in the D-loop  
* 7-methylguanosine at position 46  
* 7-methylguanosine at position 46  
* 4-thiouridine at position 8


</StructureSection>
</StructureSection>


==Function==
==Function==
Cells usually have sets of tRNAs corresponding to all 20 standard amino acids, with anticodons capable of pairing with the 61 "sense" or coding codons. Within the cell, each tRNA undergoes an aminoacylation-deacylation cycle. tRNA are attached to their cognate amino acid ('charged with' or ‘aminoacylated’) by a family of enzymes called Aminoacyl tRNA Synthetases. Charged tRNA associate with the elongation factor EF-Tu (bacteria) or EF1 (eucaryotes) complexed to GTP. These ternary complexes bind to the ribosome. If a cognate codon-anticodon interaction is formed, translation can proceed, the amino acid is incorporated at the C-terminal end of the polypetide chain and eventually, the deacylated tRNA is release for another aminoacylation-deacylation cycle.  
Cells usually have sets of tRNAs corresponding to all 20 standard amino acids, with anticodons capable of pairing with the 61 "sense" or coding codons. Within the cell, each tRNA undergoes an aminoacylation-deacylation cycle. tRNA are attached to their cognate amino acid ('charged with' or ‘aminoacylated’) by a family of enzymes called Aminoacyl tRNA Synthetases. Charged tRNA associate with the elongation factor EF-Tu (bacteria) or EF1 (eukaryotes) complexed to GTP. These ternary complexes bind to the ribosome. If codon and anticodon are complementary, translation can proceed, the amino acid is incorporated at the C-terminal end of the polypetide chain and eventually, the deacylated tRNA is release for another aminoacylation-deacylation cycle.  




Proteopedia Page Contributors and Editors (what is this?)Proteopedia Page Contributors and Editors (what is this?)

Frédéric Dardel, Wayne Decatur, Michal Harel, Alexander Berchansky, Ann Taylor, Joel L. Sussman, Karsten Theis
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