Gene expression turns a DNA sequence into a working protein through two steps: transcription (DNA to mRNA) and translation (mRNA to amino acid chain). This calculator walks a pasted DNA sequence through both steps, plus shows the complementary DNA strands, so you can check homework, lab results, or just build intuition for how the genetic code works.
How transcription and translation work here
Transcription copies one strand of DNA into a single-stranded mRNA molecule, swapping thymine (T) for uracil (U). If you paste the coding (sense) strand — the strand that already reads the same as the mRNA except for T/U — the calculator swaps T for U directly. If you paste the template (antisense) strand instead, it first computes that strand's reverse complement (recovering the coding-strand sequence), then makes the same T-to-U swap.
Translation then reads the mRNA in non-overlapping three-letter codons starting from the very first base — this is called reading frame 1. Each codon maps to one amino acid via the standard genetic code (the same 64-codon table used across nearly all known life). Translation stops as soon as it hits one of the three stop codons (UAA, UAG, UGA); everything after that point is not translated, even if more bases remain.
Reading the three result tabs
The mRNA tab is the primary output: the transcribed sequence, its length, and its base composition (counts of A, U, G, C). The Protein (Translation) tab shows the resulting amino acid chain both as a full names list (Met-Ala-...) and a compact one-letter code (MA...), plus a codon-by-codon table you can export to CSV. The Complement Strands tab shows two things about your original DNA: the literal complement (each base swapped, same order) and the reverse complement (the actual second strand of the double helix, read the normal 5' to 3' direction).
Limits and things to double-check
This tool always reads from the very first base of the mRNA (reading frame 1) — it does not search for an internal start codon (ATG) partway through a longer sequence, so if your real gene's coding sequence doesn't begin exactly where you started pasting, the translation will be shifted out of frame. It also only accepts the four standard DNA bases (A, T, G, C); ambiguity codes like N, R, or Y (common in raw sequencing reads) will be flagged as invalid rather than guessed at. For real lab or coursework use, always double-check reading frame and strand orientation against your source material.