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 inside a cell by tiny machines called ribosomes, it is messenger RNA (mRNA) that gives the instructions for building those proteins. This mRNA is made from the cell’s DNA, which acts like a blueprint.

There are 64 different codons in the genetic code. Most of these codons tell the ribosome which amino acid to add next to build a protein. But three special codons—UAG, UGA, and UAA—are called stop codons. Instead of adding an amino acid, they tell the ribosome to finish building the protein. One codon, AUG, serves as a start codon; it tells the ribosome to begin building a new protein and codes for the amino acid methionine.

Codon tables help scientists understand how the letters of the genetic code—A, U, C, and G—come together in groups of three to specify each amino acid. These tables are important because they let us read the instructions hidden inside our DNA and the DNA of all living things.

Translation table 1

The standard genetic code is shown as an RNA codon table. This is because it is messenger RNA (mRNA) that helps make proteins inside cells. The mRNA sequence comes from the DNA in our genes. Table 1 shows the standard genetic code. It also includes some less common start codons like GUG and UUG. These help begin the process of building proteins.

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. This code helps cells build proteins by reading sequences called codons. But we now know that this code can change a little depending on where you look.

For example, some tiny organisms called ciliated protozoa use different codons to make certain building blocks, or amino acids, than most other life does. Also, in the mitochondria — tiny parts inside our cells that give them energy — some codons mean different things than they usually do. Researchers have found new kinds of these codes in some bacteria too. These discoveries show that life's instructions aren't always exactly the same everywhere.