HOW MANY tRNA MOLECULES ARE THERE?
There are 20 different amino acids. There are 64 potential codons for the amino acids as shown in Table 7.15. The number of different tRNA molecules is somewhere between 20 in 64. Some tRNA can read more than one codon because there is its an exception to the complementary based pairing rule, called wobble rules. This only occurs in the three-base-pair sequences of tRNA anti-codon to the mRNA codon. The first base of tRNA can wobble a bit: does not always have to have an exact fit to a complementary base. G-C and U-A are normal. G-U and U-U use wobble rules. See Fig 7.19. HOW DOES EACH tRNA GETS ITS AMINO ACID? Each tRNA has its own enzyme, amino acid tRNA synthetase which attaches the amino acid to the tRNA. The Fig 7.20. STRUCTURE OF tRNA: tRNA has four branches and three of these have loops. The amino acid is on the end of the unlooped branch. See Fig 7.21. One loop called the anti-codon loop has three bases, the anti-codon for the amino acid at the other end of the tRNA. READING FR
