DNA and RNA codon tables

Different tables with alternate codons are used depending on the source of the genetic code, such as from a cell nucleus, mitochondrion, plastid, or hydrogenosome.

[6] Three sequences, UAG, UGA, and UAA, known as stop codons,[note 1] do not code for an amino acid but instead signal the release of the nascent polypeptide from the ribosome.

This suggests that early ribosomes read the second codon position most carefully, to control hydrophobicity patterns in protein sequences.

The first table—the standard table—can be used to translate nucleotide triplets into the corresponding amino acid or appropriate signal if it is a start or stop codon.

[22][note 4] Four novel alternative genetic codes (numbered here 34–37) were discovered in bacterial genomes by Shulgina and Eddy, revealing the first sense codon changes in bacteria.