The process in living cells in which the genetic information encoded in messenger RNA (mRNA) in the form of a sequence of nucleotide triplets (codons) is translated into a sequence of amino acids in a polypeptide chain during protein synthesis (see illustration). Translation takes place on ribosomes in the cell cytoplasm. Initiation of the process involves the formation of an initiation complex and binding of the small ribosomal subunit to the mRNA (see initiation factor). In prokaryotes binding takes place at the Shine–Dalgarno sequence, whereas in eukaryotes the small subunit binds to the 5′ cap at the end of the mRNA molecule then moves to the start codon. The ribosome moves along the mRNA ‘reading’ each codon in turn. Molecules of transfer RNA (tRNA), each bearing a particular amino acid, are brought to their correct positions along the mRNA molecule: base pairing occurs between the bases of the codons and the complementary base triplets of tRNA (see anticodon; wobble). In this way amino acids are assembled in the correct sequence to form the polypeptide chain (see elongation). Translation is terminated at a stop codon, which binds a release factor. Several ribosomes can perform translation simultaneously on the same mRNA molecule (see polyribosome), thus increasing the rate of protein synthesis. Following their release from the ribosome, most assembled polypeptides undergo some form of chemical modification to produce a fully functional protein. These post-translational modifications can take place in the endoplasmic reticulum and might include cleavage of certain amino acids; cutting or joining of polypeptides; addition of sugars to form glycoproteins; or addition of phosphate groups.

The stages of translation in protein synthesis