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GENETIC CODE REFERENCE

Codon wheel

Read codons from the center outward.

Read 5′ → 3′Download PDF
Standard code · Options

Exports use the selected code. CSV includes all 64 codons in RNA and DNA, with listed initiation and stop flags.

Genetic code reference

How to read this chart
Standard Code codon wheelGenetic code 1; NCBI genetic-code tables, September 23, 2024. Read 5′ to 3′, center outward. Generated by Codon Chart.UCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUCAGUUU · PhenylalanineUUC · PhenylalanineUUA · LeucineUUG · LeucineUCU · SerineUCC · SerineUCA · SerineUCG · SerineUAU · TyrosineUAC · TyrosineUAA · StopUAG · StopUGU · CysteineUGC · CysteineUGA · StopUGG · TryptophanCUU · LeucineCUC · LeucineCUA · LeucineCUG · LeucineCCU · ProlineCCC · ProlineCCA · ProlineCCG · ProlineCAU · HistidineCAC · HistidineCAA · GlutamineCAG · GlutamineCGU · ArginineCGC · ArginineCGA · ArginineCGG · ArginineAUU · IsoleucineAUC · IsoleucineAUA · IsoleucineAUG · MethionineACU · ThreonineACC · ThreonineACA · ThreonineACG · ThreonineAAU · AsparagineAAC · AsparagineAAA · LysineAAG · LysineAGU · SerineAGC · SerineAGA · ArginineAGG · ArginineGUU · ValineGUC · ValineGUA · ValineGUG · ValineGCU · AlanineGCC · AlanineGCA · AlanineGCG · AlanineGAU · Aspartic acidGAC · Aspartic acidGAA · Glutamic acidGAG · Glutamic acidGGU · GlycineGGC · GlycineGGA · GlycineGGG · GlycinePheLeuSerTyrStopCysStopTrpLeuProHisGlnArgIleMetThrAsnLysSerArgValAlaAspGluGlySTART5′ → 3′START HERE
NonpolarPolarAcidicBasicStopStart initiation codon
3 listed initiation codons

Listed initiation codons · table 1

These are possible starts in NCBI table 1, not a prediction that a sequence starts there. The amino acids below are their internal assignments.

UUGInternal: LeuCUGInternal: LeuAUGInternal: Met

A chosen initiator is translated as methionine. Ordinary codon lookup keeps the internal assignment; initiation needs the appropriate organism and sequence context.

Standard code (NCBI table 1). Start-codon use depends on the organism and sequence context.

Read AUG: methionine

Practice
  1. 1. Inner ringA
  2. 2. Middle ringU
  3. 3. Outer letter ringG

Move from the center outward, then read the amino acid at the edge.

Read 5′ to 3′. Use the mRNA codon, not its tRNA anticodon.

Practice reading a codon chartEight codons, two short sequences and an explained answer key.

Use the standard genetic code (NCBI table 1) for every question, independently of the chart options above. These are illustrative sequences.

Worksheet PDFAnswer key PDF

Read 5′ to 3′. For questions 1–8, use an amino acid’s name, three-letter or one-letter code, or “Stop”. For 9–10, start at the first base and give the peptide in one-letter codes; stop at the first stop codon and omit it.

Show answers and explanations
  1. Tryptophan (Trp, W)

    First base U, second G, third G: Tryptophan (Trp, W).

  2. Lysine (Lys, K)

    First base A, second A, third A: Lysine (Lys, K).

  3. Aspartic acid (Asp, D)

    First base G, second A, third C: Aspartic acid (Asp, D).

  4. Serine (Ser, S)

    First base U, second C, third U: Serine (Ser, S).

  5. Stop

    First base U, second A, third G: Stop.

  6. Methionine (Met, M)

    First base A, second U, third G: Methionine (Met, M).

  7. Proline (Pro, P)

    First base C, second C, third A: Proline (Pro, P).

  8. Valine (Val, V)

    First base G, second U, third U: Valine (Val, V).

  9. MAWKD

    AUG = Met; GCC = Ala; UGG = Trp; AAA = Lys; GAC = Asp; UAA = Stop. The stop adds no amino acid.

  10. MF

    AUG = Met; UUU = Phe; UGA = Stop. The stop adds no amino acid. Do not translate GGU after that stop.

Assignments follow NCBI’s standard code. A start codon alone does not establish where a real gene begins. More about starts and stops.

KEEP A REFERENCE

Printable RNA and DNA codon wheels

Download a one-page PDF, an editable SVG or a high-resolution PNG. These sheets use the standard genetic code (NCBI table 1). For another code, use the chart’s download controls above.

Standard-code RNA codon wheel, with all 64 codons and their amino-acid or stop assignments

RNA codon wheel

PDF — RNA codon wheelSVG — RNA codon wheelPNG — RNA codon wheel
Standard-code DNA codon wheel, with all 64 codons and their amino-acid or stop assignments

DNA codon wheel

PDF — DNA codon wheelSVG — DNA codon wheelPNG — DNA codon wheel

Download all 64 codon assignments (CSV) for a spreadsheet: coding DNA, RNA, one-letter and three-letter symbols, and full amino-acid or stop names. The CSV always uses NCBI table 1 and reads both alphabets 5′ to 3′.

Assignments from NCBI’s genetic-code tables. Read the sequence 5′ to 3′. Switching to DNA letters replaces U with T; it does not complement a strand.

How to read a codon wheel

A codon wheel, also called a genetic code wheel, is the codon chart drawn in rings. Start with the first base of your codon in the innermost letter ring. Move outward through the second and third bases, then read the amino acid at the edge. For UGG, follow U, then G, then G to reach tryptophan, abbreviated Trp or W. Always read the input codon 5′ to 3′; the wheel is not a template-strand decoder.

Search above the wheel for a codon such as UGG or an amino acid such as tryptophan. The answer appears immediately and matching sectors are highlighted. Ambiguous triplets such as GCN show every possible assignment; Inspect opens the full explanation.

The wheel and codon table show the same assignments in different arrangements. Select a segment at the outside of the wheel to inspect that codon, or use the three labeled base selectors. With a keyboard, Tab into the wheel and use Right or Down to move clockwise, Left or Up to move back. Home selects the first codon and End the last. Each step updates the highlighted reading path and the codon lookup.

Practice: translate a short mRNA

The guided lookup names the three rings for your selected codon. Try the codon practice exercise for eight codon lookups and two short translations, with explained answers and printable worksheets. The exercise always uses the standard code.

Read this messenger RNA three bases at a time from its start codon: 5′-AUG GCC UGG AAA GAC UAA-3′.

  1. AUG: A in the inner ring, U in the next ring, G in the outer letter ring, then methionine (Met, M) at the edge. It is also the start codon.
  2. GCC: alanine (Ala, A). All four codons that begin GC give alanine, so here the third base makes no difference.
  3. UGG: tryptophan (Trp, W), the only codon for it in the standard code.
  4. AAA: lysine (Lys, K).
  5. GAC: aspartic acid (Asp, D).
  6. UAA: stop. Translation ends here, and the stop codon adds no amino acid.

The peptide is Met-Ala-Trp-Lys-Asp, or MAWKD in one-letter code. For a longer sequence, the DNA-to-protein translator reads RNA or DNA in all six reading frames.

The selected codon’s lookup labels its exact Watson–Crick anticodon in both directions. If the selected code allows either an amino acid or stop, that pairing is conditional on the amino-acid outcome. For sequence pairing and modeled human or E. coli tRNA readers under the standard code, use the anticodon finder.

RNA, DNA and alternative codes

Most classroom wheels use RNA letters. Switching to DNA replaces U with T; it does not reverse or complement the sequence. If you have the DNA template strand, first establish its direction and obtain the coding-strand sequence with the reverse complement tool.

The standard genetic code is the default. The genetic-code guide compares alternative assignments, including UGA as a stop in table 1 and tryptophan in table 2. Open Options beside the download button (the slider icon on phones) for the code selector. It contains the mitochondrial and other alternative tables published by NCBI. Some assignments depend on context. A dagger marks an amino-acid assignment that can also act as termination; the note below the wheel identifies those codons. A wheel alone cannot establish the biological context that resolves such an assignment.

Open the Listed initiation codons panel below the wheel to inspect every possible start in the chosen table. It shows each codon's ordinary internal assignment and compares the start list with table 1; a listed start is not a prediction of initiation in your sequence. Code CSV in Options exports all 64 codons with both alphabets, internal assignments, initiation/stop flags and source details.

A wheel for printing

Choose an RNA or DNA sheet in the printable wheel downloads. The PDF fits on one A4 page; SVG keeps the illustration editable, and PNG is useful for inserting into slides. These permanent downloads use NCBI table 1. Changing the interactive code selector does not change them.

For the code selected in Options, download SVG or PNG. Both visibly label the full genetic-code name, NCBI table number and RNA or DNA alphabet, retain the selected codon's highlight, and explain † when assignments depend on context. The SVG stays sharp when scaled for a handout or slide. Print removes the navigation and lookup controls. For longer sequences, the DNA-to-protein translator calculates reading frames directly and reports incomplete codons and unresolved assignments. The amino acid reference provides full names alongside one-letter and three-letter abbreviations.

Inspect ambiguous codons and code differences

A wheel sector represents one exact triplet. An ambiguous input can cover several sectors: UGR expands to UGA and UGG because R means A or G. In the standard code those sectors mean Stop and tryptophan, so the inspector keeps both possibilities visible. In NCBI table 2 they both encode tryptophan. Search UGR and choose Inspect to compare the answer with the highlighted sectors.

Marked codons and the differences panel compare the selected table's internal assignments and context-dependent termination with table 1. They do not count initiation-marker differences. The full codon table's ambiguity explanation offers a row-and-column view of the same idea. Changing the table updates the wheel and selected-code SVG/PNG exports together.