5.11. tRNA – the adapter molecule

. . tRNA – the adapter molecule The transfer RNA, (tRNA) molecule of a cell acts as a vehicle that picks up the amino acids scattered through the cytoplasm and also reads specific codes of mRNA molecules. Hence it is called an adapter molecule. This term was postulated by Francis Crick. The two dimensional clover leaf model of tRNA was proposed by Robert Holley. The secondary structure of tRNA depicted in Fig. . looks like a clover leaf . In actual structure, the tRNA is a compact molecule which looks like an inverted L . The clover leaf model of tRNA shows the presence of three arms namely DHU arm, middle arm and TΨC arm. These arms have loops such $ $ * $ $ $ $ $ $ $ $ $ $ < $ $ $ & & * & & & & * & & & & & & * & * * * * * * * & $ & & * * * * * & ' ' * * & * & * \\ \ $ $ & $PLQRDFLG DWWDFKHGKHUH  HQG  HQG 6WHP ORRS \ & 9DULDEOHORRS $QWLFRGRQORRS $QWLFRGRQ 'ORRS '+ 'LK\GURXULGLQH 7K\PLGLQH3VHXGRXULGLQH DQG&\WLGLQH Fig. . Holley’s two-dimensional clover leaf model of transfer RNA XII Std Zoology Chapter XII Std Zoology Chapter Molecular Genetics catalyzed by an enzyme aminoacyl – tRNA synthetase . This is an endothermic reaction and is associated with ATP hydrolysis. different aminoacyl – tRNA synthetases are known. The power to recognize codon on the mRNA lies in the tRNA and not in the attached amino acid molecule. Fig. . Steps involved in charging tRNA. The ‘X’ denotes that for each amino acid only the corresponding specific tRNA and specific aminoacyl tRNA synthetase enzyme are involved in the charging process.