Reference
Genetic code table
The standard genetic code as a codon table: read the first base down the left, the second across the top and the third down the right to find the amino acid. Start and stop codons are marked, and the vertebrate mitochondrial reassignments are listed separately.
| First \ Second | T | C | A | G | Third |
|---|---|---|---|---|---|
| T | TTT Phe F | TCT Ser S | TAT Tyr Y | TGT Cys C | T |
| TTC Phe F | TCC Ser S | TAC Tyr Y | TGC Cys C | C | |
| TTA Leu L | TCA Ser S | TAA Stop | TGA Stop | A | |
| TTG Leu L | TCG Ser S | TAG Stop | TGG Trp W | G | |
| C | CTT Leu L | CCT Pro P | CAT His H | CGT Arg R | T |
| CTC Leu L | CCC Pro P | CAC His H | CGC Arg R | C | |
| CTA Leu L | CCA Pro P | CAA Gln Q | CGA Arg R | A | |
| CTG Leu L | CCG Pro P | CAG Gln Q | CGG Arg R | G | |
| A | ATT Ile I | ACT Thr T | AAT Asn N | AGT Ser S | T |
| ATC Ile I | ACC Thr T | AAC Asn N | AGC Ser S | C | |
| ATA Ile I | ACA Thr T | AAA Lys K | AGA Arg R | A | |
| ATG Met M | ACG Thr T | AAG Lys K | AGG Arg R | G | |
| G | GTT Val V | GCT Ala A | GAT Asp D | GGT Gly G | T |
| GTC Val V | GCC Ala A | GAC Asp D | GGC Gly G | C | |
| GTA Val V | GCA Ala A | GAA Glu E | GGA Gly G | A | |
| GTG Val V | GCG Ala A | GAG Glu E | GGG Gly G | G |
start (ATG) stop
Codons are shown as DNA; replace T with U to read them as mRNA.
Vertebrate mitochondrial code
The mitochondrial genome reads a few codons differently from the standard code. These are the reassignments for the vertebrate mitochondrial code.
| Codon | Standard | Mitochondrial |
|---|---|---|
| AGA | Arg | Stop |
| AGG | Arg | Stop |
| ATA | Ile | Met |
| TGA | Stop | Trp |
Other organisms and organelles use further variant codes; the NCBI translation tables list them all. Nuclear genes use the standard code above.
This is the standard genetic code used by nuclear genes. ATG is the usual start codon and also encodes internal methionine; TAA, TAG and TGA are stops. Use the translate tool to apply the code to a sequence.
Frequently asked
Why is it shown in DNA rather than RNA?
The rest of the toolkit works in DNA, so the table uses T for consistency. To read a codon as mRNA, replace every T with U.
Is ATG the only start codon?
It is the usual one and the only one this table marks. Some genes, especially in bacteria, start at GTG or TTG; the ribosome and context decide, not the codon alone.
Which code should I use for a mitochondrial gene?
Use the vertebrate mitochondrial reassignments shown here for vertebrate mitochondria. Other lineages differ again; the NCBI translation tables are the full reference.