Question

how many types of tRNA are present ? is it 61 as the number of possible codons are there ?

Answer 1

There are 20 types of amino acids in proteins synthesised on ribosomes. Thus, at least 20 different species of tRNAs must be present. The genetic code has 64 mRNA codons, out of which 61 specify an amino acid (rest three are nonsense codons). However, due to wobble on the third position of a codon, a maximum of 61 kinds of tRNA molecules are not needed. The number varies from one species to another. In bacteria, there may be 30-40 different tRNA molecules while in animal and plant cells about 50 different tRNA molecules are found.