Transcribe a DNA sequence to mRNA, find codons, translate to amino acids, and calculate molecular properties. Supports template and coding strand input.
Transcription — the synthesis of mRNA from a DNA template — is the first step in gene expression. In the cell, RNA polymerase reads the template strand 3'→5' and synthesizes a complementary mRNA strand 5'→3'. The resulting mRNA has the same sequence as the coding (sense) strand, except with uracil (U) replacing thymine (T).
Understanding this process is fundamental to molecular biology and genetics. Given a DNA sequence, scientists routinely need to determine the mRNA sequence, identify reading frames, locate start codons (AUG), translate codons to amino acids, and calculate the resulting protein's molecular weight. Each step follows deterministic rules based on the genetic code — the universal mapping of 64 codons to 20 amino acids and 3 stop signals.
This calculator performs the complete central dogma workflow: DNA → mRNA → protein. Enter a DNA sequence (template or coding strand), and it transcribes to mRNA, identifies all three reading frames, finds open reading frames (ORFs), translates codons to amino acids using the standard genetic code, and calculates the protein's molecular weight. It handles sequences of any length and highlights start/stop codons for easy ORF identification.
This calculator automates the tedious manual process of transcription and translation that biology students and researchers perform constantly. It eliminates errors in codon reading, frame selection, and amino acid assignment — especially for sequences longer than a few codons. This dna to mrna transcription calculator helps you compare outcomes quickly and reduce avoidable mistakes when making day-to-day care decisions. Use the estimate as a planning baseline and confirm final decisions with a qualified professional when risk is high.
Template strand → mRNA: A→U, T→A, G→C, C→G (complementary, read 3'→5'). Coding strand → mRNA: T→U (direct replacement). mRNA → Protein: AUG = Met (start), UAA/UAG/UGA = Stop, all other codons per the standard genetic code. Protein MW ≈ Σ(amino acid MW) - (n-1) × 18.02 (water lost per peptide bond).
Result: mRNA: AUGGCUAGCAAAUUU → Met-Ala-Ser-Lys-Phe
Coding strand T→U gives AUGGCUAGCAAAUUU. Reading frame 1: AUG (Met), GCU (Ala), AGC (Ser), AAA (Lys), UUU (Phe). Starts with AUG — this is an open reading frame. Protein MW ≈ 540 Da.
The genetic code maps 64 codons to 20 amino acids plus 3 stop signals. It was fully deciphered by 1966 through the work of Nirenberg, Khorana, and Holley (Nobel Prize 1968). Key features: **Universality** — nearly all organisms use the same code (with minor exceptions in mitochondria and some protists). **Degeneracy** — 18 of 20 amino acids have more than one codon. Third-position wobble (flexible base pairing) allows a single tRNA to recognize multiple codons. **Non-overlapping** — each nucleotide belongs to exactly one codon. **Comma-free** — no punctuation between codons; the reading frame, once established, continues without interruption.
An open reading frame (ORF) is a sequence of codons that begins with a start codon (usually AUG) and extends to a stop codon without interruption. In prokaryotes, the longest ORF on each strand is a strong candidate for a protein-coding gene. Eukaryotic gene prediction is more complex because of introns — the ORF in genomic DNA may be interrupted by non-coding sequences that are spliced out at the mRNA level. Bioinformatics tools like Glimmer (prokaryotes) and Augustus (eukaryotes) use statistical models trained on known genes to predict ORFs more accurately than simple length-based methods.
The molecular weight of a protein can be estimated from its amino acid composition: MW = Σ(residue weights) - (n-1) × 18.02, where 18.02 Da is the water molecule lost at each peptide bond. Average amino acid residue weight is ~110 Da, so a rough estimate is MW ≈ 110 × number of residues. More precisely, each amino acid has a specific residue weight (Gly = 57.02, Trp = 186.21), and the actual MW depends on the exact sequence. Post-translational modifications (glycosylation, phosphorylation) add additional mass not predicted from sequence alone.
The template (antisense) strand is read by RNA polymerase 3'→5' to produce mRNA. The coding (sense) strand has the same sequence as the mRNA (with T instead of U). If your textbook shows the "gene sequence," it's usually the coding strand. If RNA polymerase binds to it, it's the template strand.
There are three possible reading frames for each strand (6 total for both strands). The correct reading frame starts with AUG (the start codon for methionine) and continues without a stop codon for the expected length of the protein. In practice, the longest open reading frame (ORF) is often the correct one.
The genetic code is degenerate (redundant): most amino acids are encoded by 2-6 different codons. Leucine and serine each have 6 codons. Methionine and tryptophan each have only 1. This redundancy buffers against point mutations — many third-position changes don't alter the amino acid (synonymous mutations).
Stop codons (UAA, UAG, UGA) signal the ribosome to terminate translation. They don't code for any amino acid. Release factors recognize stop codons and catalyze the release of the completed polypeptide. In rare cases, stop codons can be "read through" by suppressor tRNAs or recoded to selenocysteine (UGA) or pyrrolysine (UAG).
Mitochondria use a slightly different genetic code. Key differences: UGA = Trp (not stop), AGA/AGG = Stop (not Arg) in vertebrate mitochondria. This calculator uses the standard (universal) genetic code. For mitochondrial sequences, adjust these codons manually.
Different organisms prefer different synonymous codons — this is codon usage bias. E. coli prefers different codons than human cells. When expressing a human gene in E. coli, rare codons can stall translation. Codon optimization tools redesign sequences to match the host organism's preferred codons without changing the protein sequence.