Each type of tRNA molecule can be attached to only one type of amino acid, so each organism has many types of tRNA (in fact, because the genetic code contains multiple codons that specify the same amino acid, there are several tRNA molecules bearing different anticodons which also carry the same amino acid). The CCA tail is a cytosine-cytosine-adenine sequence at the 3' end of the tRNA molecule. 2  The amino acid loaded onto the tRNA by aminoacyl tRNA synthetases, to form aminoacyl-tRNA, is covalently bonded to the 3'-hydroxyl group on the CCA tail.