Transfer RNA (tRNA): Difference between revisions
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[[Image:TRNA phe yeast.png|left|thumb|Standard 2D cloverleaf structure of tRNA. The shown example is phenylalanine-specific tRNA from yeast]]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/5'>In three dimensions</scene>, tRNA adopts an "L" shape, with the acceptor end <jmol> | [[Image:TRNA phe yeast.png|left|thumb|Standard 2D cloverleaf structure of tRNA. The shown example is phenylalanine-specific tRNA from yeast]]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/5'>In three dimensions</scene>, tRNA adopts an "L" shape, with the acceptor end <jmol> | ||
<jmolLink> | <jmolLink> | ||
<script> select 73-76; | <script> select 73-76; selectionHalos ON; delay 0.5; selectionHalos OFF; | ||
</script> | </script> | ||
<text>(⚞⚟)</text> | <text>(⚞⚟)</text> | ||
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</jmolLink> | </jmolLink> | ||
</jmol> on the other end. | </jmol> on the other end. | ||
At the acceptor end, amino acid are attached via the <scene name='43/433638/Threeprime/3'>2'-OH or 3'-OH group of the last nucleotide in the acceptor stem</scene>. At the opposite end of the molecule is the anticodon, which pairs with its complementary codon on the messenger RNA. | At the acceptor end, amino acid are attached via the <scene name='43/433638/Threeprime/3'>2'-OH or 3'-OH group of the last nucleotide in the acceptor stem</scene>. At the opposite end of the molecule is the <scene name='43/433638/Anticodon_loop/1'>anticodon</scene>, which pairs with its complementary codon on the messenger RNA. | ||
The two arms of the "L" <scene name='43/433638/Fullview_cartoon/20'> (cartoon)</scene> are formed by the <scene name='43/433638/Stemstacking/3'>stacking of the acceptor and TΨC-stem</scene> on one side, and of the anticodon and D-stem on the other side. <scene name='43/433638/Kissing/4'>Tertiary interactions between the TΨC- and D-loop</scene> form the corner of the L-shape and stabilize the structure. Non-Watson-Crick hydrogen bonding is important in this core (visualize interactively at [http://jmol.x3dna.org/ DSSR Jmol web interface)]). | The two arms of the "L" <scene name='43/433638/Fullview_cartoon/20'> (cartoon)</scene> are formed by the <scene name='43/433638/Stemstacking/3'>stacking of the acceptor and TΨC-stem</scene> on one side, and of the anticodon and D-stem on the other side. <scene name='43/433638/Kissing/4'>Tertiary interactions between the TΨC- and D-loop</scene> form the corner of the L-shape and stabilize the structure. Non-Watson-Crick hydrogen bonding is important in this core (visualize interactively at [http://jmol.x3dna.org/ DSSR Jmol web interface)]). | ||
In addition to the four stem loops, 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 to the four stem loops, 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<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). | '''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 [[Pseudouridine|pseudouridines]] (Ψ), methylation of either the ribose and/or the base, thiolation, reduction of uridines into dihydrouridines (D). | ||
[[Image:Pseudouridine.png|center|350px]] | [[Image:Pseudouridine.png|center|350px]] | ||
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: | 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: | ||
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See also [[Transfer RNA tour]]. | See also [[Transfer RNA tour]]. | ||
==Function== | ==Function== | ||
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'''Aminoacylation.''' Aminoacyl tRNA Synthetases pair amino acids with tRNAs. In this way, they implement the genetic code. These enzymes recognize a single tRNA (e.g. phe-tRNA) and a single amino acid (phenylalanine, in this example) and catalyze formation of an ester bond between the 3’-hydroxyl of the tRNA and the carboxylatic acid of the amino acid. | '''Aminoacylation.''' Aminoacyl tRNA Synthetases pair amino acids with tRNAs. In this way, they implement the genetic code. These enzymes recognize a single tRNA (e.g. phe-tRNA) and a single amino acid (phenylalanine, in this example) and catalyze formation of an ester bond between the 3’-hydroxyl of the tRNA and the carboxylatic acid of the amino acid. | ||
<scene name='43/433638/Cv/4'>Glutaminyl-tRNA synthetase/tRNA complex (1gtr)</scene>. The cognate aminoacid is esterified on its 3'-OH by the cognate aminoacyl-tRNA synthetase. The synthetase recognizes structural features on the tRNA, which allows it to discriminate tRNA that are specific for a given aminoacid, from all other (non-cognate) tRNA. These structural features are called identity determinants. They are often (but not exclusively) located in the anticodon sequence and/or in the so-called discriminator base (position 73), just before the 3' -CCA terminus. | <scene name='43/433638/Cv/4'>Glutaminyl-tRNA synthetase/tRNA complex (1gtr)</scene>. The cognate aminoacid is esterified on its 3'-OH by the cognate aminoacyl-tRNA synthetase. The synthetase recognizes structural features on the tRNA, which allows it to discriminate tRNA that are specific for a given aminoacid, from all other (non-cognate) tRNA. These structural features are called identity determinants. They are often (but not exclusively) located in the anticodon sequence and/or in the so-called discriminator base (position 73), just before the 3' -CCA terminus. | ||
</StructureSection> | |||
__NOTOC__ | __NOTOC__ | ||
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* [[Translation]] | * [[Translation]] | ||
* [[Ribosome]] | * [[Ribosome]] | ||
* [[Pseudouridine]] | |||
* [[2czj|tmRNA]] | * [[2czj|tmRNA]] | ||
* [[Aminoacyl tRNA Synthetase]] | |||
==References== | ==References== | ||
<references/> | <references/> | ||