Phenylalanine, anticodon synthesis

Codons that specify the same amino acid are called synonyms. Most synonyms differ only in the third base of the codon for example GUU, GUC, GUA and GUG all code for valine. During protein synthesis, each codon is recognized by a triplet of bases, called an anticodon, in a specific tRNA molecule (see Topics G10 and H2). Each base in the codon base pairs with its complementary base in the anticodon. However, the pairing of the third base of a codon is less stringent than for the first two bases (i.e. there is some wobble base-pairing ) so that in some cases a single tRNA may base-pair with more than one codon. For example, phenylalanine tRNA, which has the anticodon GAA, recognizes both of the codons UUU and UUC. The third position of the codon is therefore also called the wobble position. 

Many eucaryotic phenylalanine transfer ribonucleic acids (tRNA ) contain fluorescent components at the position adjacent to the 3 -end of an anticodon. A few related hypermodified nucleosides 1 have been isolated, their structure has been elucidated, and their chemical synthesis been performed. 

Transfer-RNA molecules participate in protein synthesis according to the genetic code at the ribosomes in the cell. The results indicate that conformational changes of the transfer-RNA molecules are important for the interaction between codon and anticodon at the ribosomes, for example. Two distinct and invariant lifetimes of the ethidium label in the anticodon loop of the transfer-RNA for the aminoaeid phenylalanine in solution indicated two conformations 2S). 

Post Synthetic Modification.— Various methods have been used to modify tRNA in order to relate its structure to its function in the reactions of protein synthesis. Excision of the Y nucleotide from yeast tRNA using the method reported last year, followed by resealing of the anticodon loop with T4 RNA ligase gives modified tRNA , with six nucleotides in the anticodon loop instead of seven, which is virtually non-chargeable with phenylalanine, although the half-molecules used to prepare the modified tRNA were chargeable. A... 

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