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Transfer RNA (abbreviated tRNA) is a small RNA chain (73-93 nucleotides) that transfers a specific amino acid to a growing protein during protien sysnthesys. It has a site for amino acid attachment and a three-base region called the anticodon that recognizes the corresponding three-base codon region on mRNA via electromagnetic base pairing. Each type of tRNA molecule can be attached to only one type of amino acid.
Transfer RNA is the "adaptor" molecule hypothesized by Francis Crick, which mediates recognition of the codon sequence in mRNA and allows its translation into the appropriate amino acid.
Structure of tRNA edit
tRNA has a complicated structure, usually visualized as a cloverleaf structure that is contorted into a kind of L shape.
Features edit
- The acceptor stem (also called the amino acid stem) is a 7-bp stem that includes the ends of the RNA chain and possibly some non-standard DNA bases, to which the amino-acid attaches, and which also contains:
- The CCA tail, which is a CCA sequence at one end of the tRNA molecule, which acts as a 'label', allowing other molecules to 'recognise' the tRNA molecule.
- a phosphate group on the other end of the RNA chain.
- The D arm is a 4 bp stem ending in a loop, which does somthing that i can't remember
- The anticodon arm is a 5-bp stem whose loop contains the anticodon, which is used to 'read' the mRNA/join to the correct position.
- The T arm is a 5 bp stem, which does blah.
- Bases that have been modified, especially by methylation, occur in several positions outside the anticodon. The first anticodon base is sometimes modified to inosine (derived from adenine) or pseudouridine (derived from uracil).
Anticodon edit
An anticodon (sometimes called nodoc from the reversed letters of the word codon)[1] is a unit made up of three nucleotides that correspond to, and are the opposite of, the three bases of the codon on the mRNA. As opposite-bases will bind to each other, anti-codons will bind to codons; each tRNA contains a specific anticodon triplet sequence that can base-pair to one or more codons for an amino acid. For example, one codon for lysine is AAA; the anticodon of a lysine tRNA might be UUU. Some anticodons can pair with more than one codon due to a phenomenon known as wobble base pairing. Frequently, the first nucleotide of the anticodon is one of two not found on mRNA: inosine and pseudouridine, which can hydrogen bond to more than one base in the corresponding codon position. In the genetic code, it is common for a single amino acid to occupy all four third-position possibilities; for example, the amino acid glycine is coded for by the codon sequences GGU, GGC, GGA, and GGG. therefore, a tRNA molecule with an anti-codon that will bond to GGx would be a glycine tRNA molecule, and the anti-codon could use wobble-base-pairing to achieve this (eg, it's anti-codon could be CCI)
To provide a one-to-one correspondence between tRNA molecules and codons that specify amino acids, 61 tRNA molecules would be required per cell. However, many cells contain fewer than 61 types of tRNAs because the wobble base is capable of binding to several, though not necessarily all, of the codons that specify a particular amino acid[2].
Aminoacylation edit
Aminoacylation is the process of adding an aminoacyl group to a compound. It produces tRNA molecules with their CCA ends covalently linked to an amino acid.
Each tRNA is aminoacylated (or charged) with a specific amino acid by an aminoacyl tRNA synthetase. There is normally a single aminoacyl tRNA synthetase for each amino acid, despite the fact that there can be more than one tRNA, and more than one anticodon, for an amino acid. Recognition of the appropriate tRNA by the synthetases is not mediated solely by the anticodon, and the acceptor stem often plays a prominent role.
tRNA/mRNA alignment edit
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