Transfer RNA (tRNA), typically 76 to 90 nucleotides in length, serves as the physical link between the mRNA sequence and the amino acid sequence of proteins. tRNA does this by carrying an amino acid to the protein synthesizing machinery comprised of a ribosome and a mRNA. tRNAs have conserved consensus structures, modified nucleotides in essential regions and each of them has a distinct anticodon triplet sequence. First of all, tRNAs have conserved consensus structures. Generally, their secondary structure can be divided into 1 accepter stem and 3 loops (ψU loop, D loop and anticodon loop). They resemble a cloverleaf. The 3’ end of the stem has an extremely conserved sequence: 5’-CCA-3’. It is the point which the corresponding amino acid attaches to. ψU and D loops are so-named due to the presence of pseudouridine and dihydro-uridine. They are side leaves of the cloverleaf, and the anticodon loop is flanked. 3D structure of tRNA is L-shaped. The corner of the “L” is formed by folding of ψU and D loops, while anticodon loop and accepter stem are perpendicularly placed on the distal ends, presenting the arms of the “L”. In addition, some nucleotides in essential regions are modified. ψU and D loops are the core body of a tRNA. Their characteristic nucleotides mediate interactions with ribosome, helping place the tRNA in the right way and stabilizing it for transformation of the amino acid to the peptide. And this is achieved by extra hydron bonds provided by pseudouridines, dihydro-uridines and other unnormal modified nucleotides. Moreover, methylations and pseudouridylation also frequently occur in the anticodon loop. These modifications mainly function in codon-anticodon recognition. Most importantly, each of tRNAs has a distinct anticodon triplet sequence. There are 20 amino acids in human cells and there are 20 tRNAs one-to-one. The attachment of specific amino acid to corresponding tRNA, or tRNA charging, is catalyzed by the aminoacyl-tRNA synthetase. Each of the 20 amino acids is attached to the appropriate tRNA by a single but dedicated tRNA synthetase. Amino acid is so small that it hard to believe one-to-one attachment merely make mistakes. Typically, less than 1 in 1000 tRNAs is charged with the incorrect amino acid. In conclusion, tRNAs play an essential role in protein translation process. They are highly conserved in structures and have special modifications to interact with the ribosome and codons properly. And to maintain correct information flow from a mRNA to a protein, each tRNA has a unique anticodon sequence. tRNAs docked on the ribosome is like a cargo ship docked on a harbor. If the anticodon in tRNA match the codon in mRNA, the amino acid, or the cargo, will be accepted and added to the newly synthesized peptide.? Note: Crystal Structure of YEAST Arginyl-tRNA Synthase complexed with the tRNA-Arg PDB: 1F7V