Codon Table Quick Reference (Standard Genetic Code): Bidirectional Codon–Amino Acid Lookup
All 64 codons of the standard genetic code (NCBI translation table 1). The two tables below can be queried directly: the first is arranged by codon position, the second allows reverse lookup by amino acid.
▶ marks start codons, ■ marks stop codons.
Codon to amino acid
| 1st · 2nd | T | C | A | G |
|---|---|---|---|---|
| TT | TTT Phe | TTC Phe | TTA Leu | TTG Leu ▶ |
| TC | TCT Ser | TCC Ser | TCA Ser | TCG Ser |
| TA | TAT Tyr | TAC Tyr | TAA Stop ■ | TAG Stop ■ |
| TG | TGT Cys | TGC Cys | TGA Stop ■ | TGG Trp |
| CT | CTT Leu | CTC Leu | CTA Leu | CTG Leu ▶ |
| CC | CCT Pro | CCC Pro | CCA Pro | CCG Pro |
| CA | CAT His | CAC His | CAA Gln | CAG Gln |
| CG | CGT Arg | CGC Arg | CGA Arg | CGG Arg |
| AT | ATT Ile | ATC Ile | ATA Ile | ATG Met ▶ |
| AC | ACT Thr | ACC Thr | ACA Thr | ACG Thr |
| AA | AAT Asn | AAC Asn | AAA Lys | AAG Lys |
| AG | AGT Ser | AGC Ser | AGA Arg | AGG Arg |
| GT | GTT Val | GTC Val | GTA Val | GTG Val |
| GC | GCT Ala | GCC Ala | GCA Ala | GCG Ala |
| GA | GAT Asp | GAC Asp | GAA Glu | GAG Glu |
| GG | GGT Gly | GGC Gly | GGA Gly | GGG Gly |
Amino acid to codons (reverse lookup)
| Amino acid | 1-letter | 3-letter | Codons (count) |
|---|---|---|---|
| Alanine | A | Ala | GCA GCC GCG GCT (4) |
| Arginine | R | Arg | AGA AGG CGA CGC CGG CGT (6) |
| Asparagine | N | Asn | AAC AAT (2) |
| Aspartic acid | D | Asp | GAC GAT (2) |
| Cysteine | C | Cys | TGC TGT (2) |
| Glutamine | Q | Gln | CAA CAG (2) |
| Glutamic acid | E | Glu | GAA GAG (2) |
| Glycine | G | Gly | GGA GGC GGG GGT (4) |
| Histidine | H | His | CAC CAT (2) |
| Isoleucine | I | Ile | ATA ATC ATT (3) |
| Leucine | L | Leu | CTA CTC CTG CTT TTA TTG (6) |
| Lysine | K | Lys | AAA AAG (2) |
| Methionine | M | Met | ATG (1) |
| Phenylalanine | F | Phe | TTC TTT (2) |
| Proline | P | Pro | CCA CCC CCG CCT (4) |
| Serine | S | Ser | AGC AGT TCA TCC TCG TCT (6) |
| Threonine | T | Thr | ACA ACC ACG ACT (4) |
| Tryptophan | W | Trp | TGG (1) |
| Tyrosine | Y | Tyr | TAC TAT (2) |
| Valine | V | Val | GTA GTC GTG GTT (4) |
| Stop | * | Stop | TAA TAG TGA (3) |
Before You Use This
This table uses DNA notation (T, not U). The corresponding mRNA position uses U: DNA TTT equals mRNA UUU, both encoding phenylalanine. The search box above accepts both notations.
This table applies to the standard genetic code only. Mitochondria, some ciliates, and mycoplasmas use alternative codon tables — for example, in vertebrate mitochondria TGA encodes tryptophan rather than a stop codon, and ATA encodes methionine rather than isoleucine. When analyzing mitochondrial genes or sequences from non-standard organisms, confirm which table applies first.
Degeneracy is not evenly distributed. Leucine, serine, and arginine each have 6 codons; methionine and tryptophan have only 1 each. Changes at the third codon position usually do not alter the amino acid (synonymous substitution), which is why third-position polymorphisms are often treated as nearly neutral sites in evolutionary analyses.
FAQ
What is the difference between an RNA codon table and a DNA codon table?
Only one letter differs: DNA uses T, mRNA uses U; everything else is identical. DNA TTT is mRNA UUU — both encode phenylalanine. The search box above accepts both notations and automatically treats U as T.
Is ATG the only start codon?
No. NCBI table 1 also designates TTG and CTG as start codons, and GTG is used as a start codon in rare cases. The vast majority of eukaryotic genes use ATG, but relying solely on ATG when annotating prokaryotic genomes will cause you to miss real genes.
Why does leucine have 6 codons while tryptophan has only 1?
This reflects the uneven degeneracy of the genetic code. Degeneracy is concentrated at the third codon position — a change there usually does not change the amino acid. This arrangement means that most point mutations at the third position are synonymous, reducing the probability that a random mutation alters the protein.
Can this table be used for mitochondrial sequences?
No. Vertebrate mitochondria use NCBI table 2, in which TGA encodes tryptophan rather than a stop codon and ATA encodes methionine rather than isoleucine. Some ciliates and mycoplasmas also have their own tables. Always confirm which table applies before analyzing non-nuclear genomic sequences.
How reliable is the data in this table?
All 64 codons have been individually verified against the NCBI official Genetic Codes page (table 1), and degeneracy for all 21 amino acid classes, all 3 stop codons, and start codon designations have been independently cross-checked. The table on this page is generated programmatically from that data — there is no manual transcription step.
Related tools
Amino Acid Properties Reference: Molecular Weight, Side-Chain pKa, Hydrophobicity, and Codon Count
Properties of all 20 standard amino acids: residue mass, side-chain pKa, Kyte-Doolittle hydrophobicity, and codon count. Searchable by code or name.
Restriction Enzyme Recognition Sequences Reference & Cut-Site Finder
Recognition sequences, cut sites, end types, and average spacing for 30 common restriction enzymes; paste any sequence to locate cut sites (linear or circular).
Non-Standard Genetic Code Tables: Mitochondrial, Bacterial, and Ciliate Codon Differences (NCBI transl_table Reference)
All 27 NCBI genetic code tables with per-codon differences from the standard table, searchable by table number or codon.
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