tRNA structure:

Transfer  RNA  (tRNA)  molecules  play  an  very important  role  in  protein  synthesis. Every tRNA becomes covalently bonded to a specific amino acid  to  create  aminoacyl- transfer RNA that  recognizes  the  corresponding  codon  in mRNA  and  ensures   in which  the  correct  amino  acid  is  added  to  the  growing polypeptide  chain. The transfer RNAs are small molecules, only 74-95 nt long, that form distinctive   cloverleaf secondary structures shown in the figure through internal base pairing. The stem-loops of the cloverleaf are called as arms:

-  the anticodon arm holds in its loop the three nucleotides of the anticodon that will form base pairs with the complementary  codon in mRNA in during translation;

- the DHU or D arm (with its D loop) contains dihydrouracil, and strange pyrimidine;

- the   TΨC or T    arm   (with   its  T  loop)   holds   another   strange base, pseudouracil  (indicate Ψ) in the sequence TΨC;

- Some transfer RNAs also have a variable arm (optional arm) that is 3-21 nt in size.

The other notable feature is the amino acid acceptor stem.  That is where the amino acid becomes attached, at the 3 OH groups of the 3 -CCA sequence.

The three-dimensional structure of tRNA that was shown in the figure is even more complex because of additional interactions between the various units of secondary structure.

Figure:  (a) Cloverleaf secondary  structure of tRNA; (b) tertiary structure of tRNA (from Genetics: a Molecular Approach, second edition, T.A. Brown, Kluwer Academic Publishers, with permission).