DNA and RNA codon tables

A codon table can be used to translate a genetic code into a sequence of amino acids. When proteins are made in a cell by ribosomes, it is messenger RNA (mRNA) that directs protein synthesis. The mRNA sequence is determined by the sequence of genomic DNA. In this context, the standard genetic code is called 'translation table 1' among other tables. It can also be shown in a DNA codon table.

There are 64 different codons in the genetic code. Most of these codons specify an amino acid. Three special sequences, UAG, UGA, and UAA, known as stop codons, do not code for an amino acid. Instead, they signal the end of the protein being made. In the standard code, the sequence AUG—read as methionine—can serve as a start codon. Along with other signals such as an initiation factor, it begins the process of making a protein. Sometimes, other codons like GUG or UUG can also act as start codons.

The standard table helps translate groups of three nucleotide letters, called triplets, into the corresponding amino acid or signal. There is also an inverse table that works the other way: if you know the amino acid, it can help figure out the possible triplet code. Because multiple codons can code for the same amino acid, special notation from the International Union of Pure and Applied Chemistry is sometimes used, called nucleic acid notation.

Translation table 1

The standard genetic code helps cells make proteins. It reads instructions from DNA and turns them into messages using a molecule called messenger RNA (mRNA). This is like a translation table. It matches sets of three letters, called codons, to special building blocks of proteins named amino acids. Table 1 shows some special start codons, GUG and UUG, that help begin this process.

Alternative codons in other translation tables

Further information: List of genetic codes

Scientists once thought that the genetic code was the same for all living things. They believed that a group of three letters, called a codon, would always create the same building block of a protein. But we now know that the genetic code can change over time. This means a codon can sometimes create a different building block, depending on where it is found.

For example, researchers found that certain codons like AUA, UGA, AGA, and AGG work differently in the energy factories inside our cells. Even codons that usually tell a cell to stop building a protein can change meaning. In some tiny organisms, these codons make an amino acid called glutamine instead. Scientists have also found new ways codons work in some bacteria, showing that the genetic code is not as fixed as we once thought.