translation

Translation is exactly what its name suggests: converting a message from one language into another. Here the nucleic-acid language of mRNA (written in four bases) is translated into the protein language of amino acids (which uses twenty kinds). The translator is the ribosome, and the dictionary is the genetic code.

The ribosome moves along the mRNA three bases at a time, reading each codon. For each codon, a transfer RNA arrives carrying the matching amino acid, and the ribosome links that amino acid onto the growing chain. Codon by codon, a polypeptide is assembled in the precise order the gene specified.

Translation begins at a start codon, continues in a fixed reading frame, and ends at a stop codon, where the finished protein is released. It is fast and tightly regulated, and the same mRNA can be translated many times to make many copies of one protein.