All tRNAs have about 73 to 93 nucleotides that fold into four base-paired stems and three loops, a structure which looks like a clover leaf in secondary structure. It is "L" shaped in the three-dimensional structure. The anticodon loop has triplet at the tip which base pairs with the corresponding codon in mRNA. The 3' end has CCA sequence. Attachment of an amino acid to the 3’ adenosine yields an aminoacyl-tRNA and therefore the CCA site is called as amino acid binding site. Transfer-RNA has 7-15% post-transcriptionally modified bases. Dihydrouridine (D) is nearly always found in the D-loop and serves as aminoacyl synthetase recognition and binding loop while the T psi C loop binds the charged tRNA-amino acid to the ribosome.