DNA to mRNA Transcription Calculator
Transcribe a DNA template strand into its mRNA, or convert a coding length in base pairs into mRNA nucleotides, codons and the resulting protein length.
How it works
Transcription is 1:1 — mRNA nucleotides = transcribed template bases · Template→mRNA: A→U, T→A, G→C, C→G · Codons = ⌊nucleotides ÷ 3⌋ · Protein length ≈ codons − 1 (stop codon)
During transcription RNA polymerase reads the DNA template strand and builds a complementary mRNA, base-for-base, so the mRNA has the same number of nucleotides as the transcribed region. The template pairs A→U, T→A, G→C and C→G. Dividing the mRNA length by three gives the number of codons, and because one codon signals stop, the protein is about one amino acid shorter than the codon count. This simple model ignores introns, the 5′ cap, poly-A tail and untranslated regions.
Worked example
A 300 bp coding sequence transcribes to 300 mRNA nucleotides. That is 300 ÷ 3 = 100 codons, and with one stop codon the protein is about 99 amino acids long.
Sources: Transcription (biology) — Wikipedia
Frequently asked questions
Is mRNA the same length as the DNA it comes from?
For the transcribed region, yes — transcription copies the template base-for-base. In eukaryotes the primary transcript is then spliced (introns removed) and gets a cap and poly-A tail, so the mature mRNA differs from the raw gene length.
How do I get the mRNA from the template strand?
Replace each template base with its RNA complement: A→U, T→A, G→C, C→G, reading 5′→3′ on the new mRNA. The coding (sense) strand looks identical to the mRNA except T becomes U.
Why is the protein one amino acid shorter than the codon count?
One of the codons is a stop signal (UAA, UAG or UGA) that ends translation without adding an amino acid, so a 100-codon message encodes about 99 residues.
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Educational estimate, not medical or laboratory advice — verify formulas, units and assumptions for your specific organism or protocol.