This codon calculator runs the central dogma end to end: paste a DNA sequence and it transcribes the mRNA, reads the codons in frame, and translates them into the amino acid sequence using the standard genetic code — flagging start and stop codons along the way.
DNA → RNA → Protein, in One Pass
Transcription copies the coding strand into mRNA (T becomes U); translation reads that message in codons — nucleotide triplets — each specifying one amino acid per the standard genetic code: 61 sense codons for 20 amino acids (the code is redundant, mostly at the third “wobble” position) plus 3 stop codons. Sequence hygiene partners live on this hub: base composition at our GC Content Calculator, and the partner-strand view at the Reverse Complement Calculator — note this tool expects the coding strand; paste a template strand and you should reverse-complement it first. Part of our Biology Calculators collection.
Worked Example (Verified)
DNA: ATG GCT TTT GGA TAA (the widget’s default):
- mRNA: AUG GCU UUU GGA UAA
- Protein: Met – Ala – Phe – Gly – Stop (single-letter: M A F G *) — a tidy four-residue peptide with a textbook start and stop
- Shift the frame by one base and the same letters decode to entirely different amino acids — the reading frame is information, which is why frameshift mutations (insertions/deletions not divisible by 3) are so destructive
- Try TAA vs TAG vs TGA: three different spellings of “stop” (opal/amber/ochre in geneticist slang)
Reading the Code Like a Biologist
- Degeneracy protects: leucine, serine and arginine each claim 6 codons — many point mutations are silent at the protein level.
- Start is context, not just ATG: translation initiates at the first AUG in a favorable (Kozak) context; internal ATGs simply code Met.
- The “universal” code has known dialects — mitochondria and some ciliates reassign codons (e.g., TGA = Trp in mitochondria); this calculator uses the standard code and says so.
- Real translation ends at the stop; sequences here that run off the end report exactly that rather than inventing a terminus.
Related Tools
- Reverse Complement Calculator — get the coding strand from the template
- GC Content Calculator — composition and melting estimates
- Biology Calculators — the full collection
Frequently Asked Questions
How do you translate a DNA sequence into protein?
Replace T with U for the mRNA, group into triplets from the start codon, and look each codon up in the genetic code table: AUG = Met, GCU = Ala, UUU = Phe, GGA = Gly, UAA = Stop — exactly the worked example above.
What are the three stop codons?
UAA (ochre), UAG (amber) and UGA (opal) in mRNA — TAA, TAG, TGA in DNA spelling. They recruit release factors instead of tRNAs, ending translation; readthrough and reassignment exist in nature but are exceptions with their own machinery.
What is a reading frame, and why does it matter?
The phase in which triplets are grouped: a sequence has 3 frames per strand (6 with the reverse strand), usually only one encoding the intended protein (the open reading frame). The frame selector here lets you inspect the others — a vivid demonstration of why indels shift everything downstream.
Why are there 64 codons but only 20 amino acids?
4³ = 64 triplets must cover 20 amino acids plus punctuation, so the code is degenerate: most amino acids have 2–6 codons, differing at the third base. The redundancy buffers mutations and is a rich subject in evolutionary biology.
Should I paste the coding or template strand?
The coding (sense) strand — the one whose sequence matches the mRNA (with T for U). If your sequence is the template strand, run it through the Reverse Complement Calculator first; translating the template directly gives a meaningless frame.
Is this codon calculator free?
Yes — free, instant, and sequences never leave your browser.