Transfer RNA (tRNA) is a small RNA molecule that plays a role in protein synthesis. Typically tRNAs have highly conserved sequences and four-armed cloverleaf secondary structures formed by base pairing within the tRNA resulting in the formation of hairpin loops. Exceptions to this cloverleaf structure occur in mitochondrial and nematode tRNAs. There are two parts to the tRNA that are involved in protein synthesis: the anticodon that recognizes and binds to the complementary codon in the mRNA transcript; and the amino-acid binding site. The aminoacyl-tRNA synthetase are involved in pairing the amino acid with its cognate tRNA. Amino acids are transferred from the amino-acyl tRNA to the growing peptide chain via the formation of a peptide bond.