The Structure of Transfer RNA (tRNA)

-Small, ~ 70-90 ribonucleotides long (remember, they are transcribed from certain DNA sequences)
-Single-stranded but folded into a particular 3D shape (Fig. 2). The 3D shape is held together by intrachain hydrogen bonds between complementary base pairs (Fig. 1). Like all RNA molecules, they have a 3'-OH terminus, but the opposite end terminates with a 5' monophosphate rather than a 5'-triphosphate, because tRNA molecules are cut from a large primary transcript.

 see Figure of tRNA in text book (P. 274-275)

Note the D arm which contains dihydrouracil, the T psi C arm which contains a thymine, a pseudouridine, and a cytosine. Also note the presence of the extra arm. In class I tRNAs the extra arm is quite small, in class II RNAs the extra arm is long.

 Note the 4 regions of molecule where you have intrastrand hydrogen bonding.

 Note the location of the anticodon. The anticodon is a sequence of 3 bases that can form base pairs with a codon sequence in the mRNA (Fig. 3).

 No tRNA has anticodon complementary to stop codons UAG, UAA, or UGA

 tRNAs are initially made as part of a somewhat longer RNA transcript. First cut out, then completed by an enzyme that adds the three nucleotides CCA to the 3'end. Note that the 3' ribonucleotide base is ALWAYS adenine.
 

 The amino acid attachment site is located at the 3'OH terminus
The amino acid, corresponding to the specific tRNA anticodon, is covalently linked to this terminus. Amino acids will come off to form polypeptide chain during protein synthesis.

 tRNAs are actually Amino acid carriers

 With the help of a specific enzyme the tRNA recognizes and binds to a specific amino acid.
The enzymes are termed: aminoacyl tRNA synthetases (Fig. 4).

 
There is a different synthetase enzyme for every amino acid. A specific aminoacyl tRNA synthetase matches the amino acid with the anticodon; to do so, the enzyme must be able to distinguish one tRNA molecule from another. The necessary distinction is provided by an as yet ill-defined region encompassing many parts of the tRNA molecule called the recognition site. At the opposite end of the molecule is a loop which contains the anticodon. As the mRNA codons are read, only the appropriate tRNA can hydrogen bond with the codon by virtue of the anticodon. [See Figure 7.2 in text of how enzyme adds amino acid to the tRNA.]

G A A  mRNA codon
 |   |   |
C U U tRNA anticodons

 tRNA Terminology

charged - tRNA with amino acid attached
uncharged - tRNA, no amio acid
mischarged - incorrect amino acid

 The different tRNA molecules and synthetases are designated by stating the name of the amino acid that can be linked to a particular tRNA molecule by a specific synthetase:
i.e. leucyl-tRNA synthetase attaches leucine to tRNA^Leu

 Only the tRNA molecule, not its attached amino acid determines where the amino acid is added during protein synthesis. If you mischarge a tRNA it will put wrong amino acid in according to the anticodon.

tRNA Tutorial for Phe-tRNA