The anticodon location and the amino acid acceptor region of tRNA are far apart in the primary sequence as well as in the tertiary structure. Then how a particular set of codon triplet translated to a specific amino acid?
Anticodon sequence and a few more nucleotides (very often last nucleotide pair before aa acceptor site in tRNA) are recognized by specific aminoacyl t-RNA synthetases which are responsible for attachement of particular aminoacid to tRNA. So anticodon loop as well as few characteristic points in tRNA structure determine interactions with particular tRNA-synthetase resulting in proper anticodon-aa conection.
Joanna is right, but you have to read her reply very carefully. The last few nucleotides before the acceptor A nucleotide are invariable (the unpaired tail is CCA in all the different tRNAs), but the paired region before the CCA can be important in recognition.
Some tRNAs have 2 and some have 3 specificity regions in their structure and these regions are recognized by a set of amino acid residues in the different AA-tRNA-synthetases. One of the specificity regions is always the anticodon, while others are towards the middle and towards the end of the tRNA tertiary structure.
In fact, when you look at the structure of tRNA - AA-tRNA-synthetase complexes, they mostly seem very tight and there might be other contacts (outside the core specificity regions) in play. Each tRNA is of a little bit different shape and so are the different enzymes diferent in shape. Only those with compatible surfaces can form a complex, which is a prerequisite for the catalytic addition of the amino acid.
The importance of single tRNA nucleotides is shown in the figure (see link) with yellow circles - the bigger it is, the more important this position is for enzyme recognition and specificity.
http://oregonstate.edu/instruct/bb451/winter14/stryer7/CH30/figure_30_12.jpg
Joanna and Marko provided excellent responses. I just would like to add that some aminoacyl tRNA synthetases also have have an additional editing domain that allows "proofreading" activitiy. When sometimes the wrong aminoacid is recognized, these enzymes are capable of hydrolyzing misactivated amino acids either before or after transfer to noncognate tRNAs.
So this is the egg and chicken problem at the molecular level... Thank you everybody.
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