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MasterMath

Codon to Amino Acid Calculator

Translates a messenger RNA into the chain of amino acids it codes for, with the full codon table and the stop codon where it falls. It starts at the first AUG, which is what the ribosome does, or at the first base if the exercise asks for it.

Peptide in one-letter code

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Peptide in one-letter code—
Peptide in three-letter code—
Amino acids—
Reading starts at—
Stop codon—
Leftover bases—
#CodonAmino acidLetter

How this was worked out

    The formula

    Every three bases of RNA are one codon, and every codon one amino acid

    What it means

    The genetic code reads bases three at a time. With four bases there are 64 codons for twenty amino acids, so there are spares: almost every amino acid has several codons that mean the same thing, and they nearly always differ in the third base. Three codons code for nothing and order a stop: UAA, UAG and UGA. AUG does two jobs at once, because it is methionine and also the start signal.

    How to work it out by hand

    1. Find the first AUG, which is where the ribosome starts reading
    2. Split the sequence into groups of three from there
    3. Look each codon up in the table and note its amino acid
    4. Stop at UAA, UAG or UGA: that codon adds no amino acid

    What is worth knowing

    The reading frame is everything: shifting the start by a single base gives a completely different protein, which is why inserting one nucleotide is so destructive while inserting three barely shows. If one or two bases are left over at the end they are reported separately rather than padded out. This is the standard code; human mitochondria use a variant in which UGA is tryptophan and AGA and AGG are stops.

    Frequently asked questions

    Can I paste DNA instead of RNA?

    Swap the Ts for Us first, or use the complementary strand calculator, which gives you the RNA directly. Here a T is reported as an invalid letter.

    Why is there no amino acid for the stop codon?

    Because it codes for none. UAA, UAG and UGA only mark where the protein ends.

    What if there is no AUG?

    There is no translation from a start codon. Switch the option to "at the first base" if you want to read the sequence as it stands.

    Why do several codons give the same amino acid?

    Because there are 64 codons for 20 amino acids. That redundancy cushions errors: many changes in the third base leave the protein untouched.

    Does this table apply to every organism?

    To almost all of them: the standard code is close to universal. Mitochondria and a few protozoa have a handful of exceptions.