There is a set of small ‘transfer RNAs’ (tRNA), each about 70 building blocks long. Each of the tRNAs attaches itself selectively to one, and only one, of the 20 kinds of natural amino acids. At the other end of the tRNA molecule is an ‘anti-codon’, a triplet precisely complementing the short mRNA sequence (codon) that specifies the particular amino acid according to the genetic code. As the tape of mRNA moves through the reading head of the ribosome, each codon of the mRNA binds to a tRNA with the right anti-codon.
