the anticodon site on a trna molecule is at a site.
where is the anticodon site on a trna molecule?
a site
while the specific nucleotide sequence of an mrna specifies which amino acids are incorporated into the protein product of the gene from which the mrna is transcribed, the role of trna is to specify which sequence from the genetic code corresponds to which amino acid. the mrna encodes a protein as a series of contiguous codons, each of which is recognized by a particular trna. one end of the trna matches the genetic code in a three-nucleotide sequence called the anticodon. the anticodon forms three complementary base pairs with a codon in mrna during protein biosynthesis. on the other end of the trna is a covalent attachment to the amino acid that corresponds to the anticodon sequence. each type of trna molecule can be attached to only one type of amino acid, so each organism has many types of trna. because the genetic code contains multiple codons that specify the same amino acid, there are several trna molecules bearing different anticodons which carry the same amino acid.
transfer rna
in the genetic code, there are 4 = 64 possible codons (tri-nucleotide sequences). for translation, each of these codons requires a trna molecule with a complementary anticodon. if each trna molecule is paired with its complementary mrna codon using canonical watson-crick base pairing, then 64 types (species) of trna molecule would be required. in the standard genetic code, three of these 64 mrna codons (uaa, uag and uga) are stop codons. these terminate translation by binding to release factors rather than trna molecules, so canonical pairing would require 61 species of trna. since most organisms have fewer than 45 species of trna, some trna species must pair with more than one codon. in 1966, francis crick proposed the "wobble hypothesis" to account for this. he postulated that the 5' base on the anticodon, which binds to the 3' base on the mrna, was not as spatially confined as the other two bases, and could, thus, have non-standard base pairing. crick creatively named it for the small amount of play that occurs at this third codon position. movement ("wobble") of the base in the 5' anticodon position is necessary for small conformational adjustments that affect the overall pairing geometry of anticodons of trna.
wobble base pair