El nombre de la rosa

Páginas: 4 (854 palabras) Publicado: 24 de marzo de 2011
Transfer RNA

Transfer RNA (tRNA) is a small RNA molecule (usually about 74-95 nucleotides) that transfers a specific active amino acid to a growing polypeptide chain at the ribosomal site ofprotein synthesis during translation. It has a 3' terminal site for amino acid attachment. This covalent linkage is catalyzed by an aminoacyl tRNA synthetase. It also contains a three base region calledthe anticodon that can base pair to the corresponding three base codon region on mRNA. Each type of tRNA molecule can be attached to only one type of amino acid, but because the genetic code containsmultiple codons that specify the same amino acid, tRNA molecules bearing different anticodons may also carry the same amino acid.
The structure of tRNA can be decomposed into its primary structure, itssecondary structure (usually visualized as the cloverleaf structure), and its tertiary structure (all tRNAs have a similar L-shaped 3D structure that allows them to fit into the P and A sites of theribosome). The cloverleaf structure becomes the 3D L-shaped structure through coaxial stacking of the helices which is a common RNA Tertiary Structure motif.
The 5'-terminal phosphate group.
Theacceptor stem is a 7-base pair (bp) stem made by the base pairing of the 5'-terminal nucleotide with the 3'-terminal nucleotide (which contains the CCA 3'-terminal group used to attach the amino acid).The acceptor stem may contain non-Watson-Crick base pairs.
The CCA tail is a cytosine-cytosine-adenine sequence at the 3' end of the tRNA molecule. This sequence is important for the recognition oftRNA by enzymes critical in translation. In prokaryotes, the CCA sequence is transcribed in some tRNA sequences. In most prokaryotic tRNAs and eukaryotic tRNAs, the CCA sequence is added duringprocessing and therefore does not appear in the tRNA gene.
The D arm is a 4 bp stem ending in a loop that often contains dihydrouridine.
The anticodon arm is a 5-bp stem whose loop contains the anticodon....
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