<Li> The CCA tail is a cytosine - cytosine - adenine sequence at the 3' end of the tRNA molecule . 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 . This sequence is important for the recognition of tRNA by enzymes and 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 during processing and therefore does not appear in the tRNA gene . </Li> <Li> The D arm is a 4 - to 6 - bp stem ending in a loop that often contains dihydrouridine . </Li> <Li> The anticodon arm is a 5 - bp stem whose loop contains the anticodon . The tRNA 5' - to - 3' primary structure contains the anticodon but in reverse order, since 3' - to - 5' directionality is required to read the mRNA from 5' - to - 3' . </Li> <Li> The T arm is a 4 - to 5 - bp stem containing the sequence TΨC where Ψ is pseudouridine, a modified uridine . </Li>

A triplet of nucleotides in trna is called an