Codon ChartHow to convert DNA to mRNA
In transcription, RNA polymerase reads the DNA template strand 3′ to 5′ and builds mRNA 5′ to 3′, pairing each template base with its partner: A with U, T with A, C with G and G with C. The mRNA therefore has the same sequence as the other DNA strand, the coding strand, with U in place of T.
Paste your strand, choose which strand it is, and choose Convert. The result lines up the coding strand, the template strand, the mRNA, each codon's tRNA anticodon and the amino acid, codon by codon, like a transcription and translation worksheet. Spaces, line numbers and 5′/3′ labels in your sequence are ignored; the labels are checked against the strand you chose.
Worked example: template strand to amino acids
This is the example in the converter, an illustrative sequence rather than a natural gene:
| Row | Sequence |
|---|---|
| Template DNA | 3′-TAC CGG ACC TTT GTA ATT-5′ |
| Coding DNA | 5′-ATG GCC TGG AAA CAT TAA-3′ |
| mRNA | 5′-AUG GCC UGG AAA CAU UAA-3′ |
| tRNA anticodons | UAC, CGG, ACC, UUU, GUA, each written 3′ to 5′ |
| Amino acids | Met-Ala-Trp-Lys-His, then the UAA stop codon |
Each template base pairs with one mRNA base: TAC becomes AUG, the start codon, and ATT becomes UAA, a stop codon. The codon chart gives each codon's amino acid.
Which strand do you have?
The mRNA depends on which strand you start from and which way it is written. All four of these describe the same gene fragment and give the same mRNA, 5′-AUGGCCUGGAAACAUUAA-3′:
| You have | Written | Example | What the converter does |
|---|---|---|---|
| Template strand | 3′ to 5′ | TAC CGG ACC TTT GTA ATT | Pairs each base |
| Template strand | 5′ to 3′ | TTA ATG TTT CCA GGC CAT | Reverses it, then pairs each base |
| Coding strand | 5′ to 3′ | ATG GCC TGG AAA CAT TAA | Replaces T with U |
| mRNA | 5′ to 3′ | AUG GCC UGG AAA CAU UAA | Reads it as it is |
Classroom exercises often give the template strand 3′ to 5′, so its first triplet pairs straight into the first codon. Sequence databases write every strand 5′ to 3′; a template strand written that way has to be reversed before pairing. To flip a strand without transcribing it, use reverse complement.
Codons, anticodons and amino acids
Each three-base codon of the mRNA pairs with a tRNA anticodon carrying one amino acid. The two run antiparallel, so an anticodon written 3′ to 5′ under its codon is the codon's complement: AUG pairs with 3′-UAC-5′. The converter shows those exact Watson–Crick partners. Real tRNAs often read several codons through looser "wobble" pairing at the third position, so a cell needs fewer than 61 tRNAs. Codon versus anticodon explains the orientation in more detail.
Amino acids come from the standard genetic code (NCBI table 1). The amino acid chart lists all 20 with their three-letter and one-letter codes.
Where translation starts and stops
By default the converter reads from the first base, as worksheets do. Choose The first AUG to start at the first start codon instead: a real mRNA is translated from its start codon, not from its first base. Translation ends at the first stop codon, UAA, UAG or UGA. No tRNA reads a stop codon; a release factor ends translation, so the converter shows no anticodon there.
A longer sequence can hold a gene in any of six reading frames. To translate every frame or find complete open reading frames, use DNA to protein.
Sources: OpenStax Biology 2e, Prokaryotic Transcription and Ribosomes and Protein Synthesis; NHGRI glossary: transcription, messenger RNA and anticodon; codon assignments from NCBI table 1.