tRNA

Transfer RNA (tRNA) is involved in translation. Four double-helical segments fold tRNA into a cloverleaf shape and additional hydrogen bonds further folds the molecule into L-shape. The tertiary structure consists of D-arm, anti-codon in anti-codon arm, T-arm, variable loop, adaptor stem and CCA tail. The ribonucleotides in tRNA are mostly A, U, C, G but some modified bases are also found in the molecule. For example, pseudouridine is found in T-arm and D-arm contains dihydrouridine. They are the recognition sites for ribosome attachment and aminoacyl-tRNA synthetase respectively. The anti-codon includes three nucleotides which are complementary to the codon sequence on the messenger RNA (mRNA) made after transcription. But there are exceptions in wobble base pairing in which some anti-codon can pair with more than one codon. With the help of aminoacyl-tRNA synthetase and the presence of ATP, specific amino acid is covalently attached to the 3’ CCA end in a process called aminoacylation. During translation, aminoacyl-tRNA enters the ribosome and add amino acid to C-terminal of the growing polypeptide chain.