Codon Table — The Standard Genetic Code
A codon table maps each of the 64 three-letter nucleotide codons to the amino acid it encodes. The standard genetic code (NCBI table 1) has 61 sense codons for 20 amino acids, one start codon (AUG → methionine) and three stop codons (UAA, UAG, UGA). Use the toggle to switch between DNA and RNA bases.
| 1st ↓ / 2nd → | T | C | A | G | 3rd |
|---|---|---|---|---|---|
| T | TTTPhe · F | TCTSer · S | TATTyr · Y | TGTCys · C | T |
| TTCPhe · F | TCCSer · S | TACTyr · Y | TGCCys · C | C | |
| TTALeu · L | TCASer · S | TAAStop | TGAStop | A | |
| TTGLeu · L | TCGSer · S | TAGStop | TGGTrp · W | G | |
| C | CTTLeu · L | CCTPro · P | CATHis · H | CGTArg · R | T |
| CTCLeu · L | CCCPro · P | CACHis · H | CGCArg · R | C | |
| CTALeu · L | CCAPro · P | CAAGln · Q | CGAArg · R | A | |
| CTGLeu · L | CCGPro · P | CAGGln · Q | CGGArg · R | G | |
| A | ATTIle · I | ACTThr · T | AATAsn · N | AGTSer · S | T |
| ATCIle · I | ACCThr · T | AACAsn · N | AGCSer · S | C | |
| ATAIle · I | ACAThr · T | AAALys · K | AGAArg · R | A | |
| ATGMet · M · start | ACGThr · T | AAGLys · K | AGGArg · R | G | |
| G | GTTVal · V | GCTAla · A | GATAsp · D | GGTGly · G | T |
| GTCVal · V | GCCAla · A | GACAsp · D | GGCGly · G | C | |
| GTAVal · V | GCAAla · A | GAAGlu · E | GGAGly · G | A | |
| GTGVal · V | GCGAla · A | GAGGlu · E | GGGGly · G | G |
Start codon (ATG → Met)Stop codon (TAA, TAG, TGA)
Start and stop codons
Translation begins at the start codon AUG (ATG in DNA), which also codes for methionine — that is why most proteins start with Met. It ends at one of the three stop codons, UAA, UAG or UGA, which do not encode any amino acid and release the finished polypeptide.
DNA vs RNA codons
The DNA and RNA codon tables are identical except that RNA uses uracil (U) wherever DNA uses thymine (T). During transcription the DNA coding strand is copied base-for-base into mRNA, with T replaced by U. See DNA vs RNA for the full picture.
Amino acids and their codons
All 20 standard amino acids, with their one- and three-letter codes, side-chain class and every codon that encodes them.
| Amino acid | 3-letter | 1-letter | Class | Codons (DNA) |
|---|---|---|---|---|
| Alanine | Ala | A | Nonpolar | GCT, GCC, GCA, GCG |
| Arginine | Arg | R | Basic | CGT, CGC, CGA, CGG, AGA, AGG |
| Asparagine | Asn | N | Polar | AAT, AAC |
| Aspartic acid | Asp | D | Acidic | GAT, GAC |
| Cysteine | Cys | C | Polar | TGT, TGC |
| Glutamic acid | Glu | E | Acidic | GAA, GAG |
| Glutamine | Gln | Q | Polar | CAA, CAG |
| Glycine | Gly | G | Nonpolar | GGT, GGC, GGA, GGG |
| Histidine | His | H | Basic | CAT, CAC |
| Isoleucine | Ile | I | Nonpolar | ATT, ATC, ATA |
| Leucine | Leu | L | Nonpolar | TTA, TTG, CTT, CTC, CTA, CTG |
| Lysine | Lys | K | Basic | AAA, AAG |
| Methionine | Met | M | Nonpolar | ATG |
| Phenylalanine | Phe | F | Nonpolar | TTT, TTC |
| Proline | Pro | P | Nonpolar | CCT, CCC, CCA, CCG |
| Serine | Ser | S | Polar | TCT, TCC, TCA, TCG, AGT, AGC |
| Threonine | Thr | T | Polar | ACT, ACC, ACA, ACG |
| Tryptophan | Trp | W | Nonpolar | TGG |
| Tyrosine | Tyr | Y | Polar | TAT, TAC |
| Valine | Val | V | Nonpolar | GTT, GTC, GTA, GTG |
| Stop | Stop | * | — | TAA, TAG, TGA |
Frequently asked questions
- What is a codon table?
- A codon table (or genetic code chart) maps each of the 64 possible three-nucleotide codons to the amino acid it encodes during translation. The standard code has 61 sense codons specifying 20 amino acids, plus three stop codons.
- What is the start codon?
- AUG (ATG in DNA) is the start codon. It both initiates translation and codes for methionine, so most proteins begin with methionine.
- What are the stop codons?
- There are three stop codons — UAA, UAG and UGA (TAA, TAG and TGA in DNA). They signal the ribosome to terminate translation and do not encode an amino acid.
- What is the difference between a DNA and an RNA codon table?
- They are identical except that RNA uses uracil (U) where DNA uses thymine (T). For example, the DNA codon ATG corresponds to the mRNA codon AUG. Use the DNA/RNA toggle above to switch between them.
- Why do several codons code for the same amino acid?
- The genetic code is degenerate (redundant): 61 codons encode just 20 amino acids, so most amino acids have two or more synonymous codons. Synonymous codons usually differ in the third 'wobble' position.