There are about 64 different combinations of three nucleotide bases into codons. The combinations, however, only code for 20 amino acids hence some codons are redundant. When the mRNA forms a scaffolding with the ribosome, the tRNA with the right anticodon (sequence complementary to the codon on the mRNA) to the codon on the A site of the ribosome, leaves its amino acid at the site of chain elongation (P-site) and exits at the E-site.
