How to translate DNA to protein by hand
First transcribe: the mRNA has the same sequence as the DNA coding strand, except every thymine (T) becomes uracil (U). Then read the mRNA in non-overlapping groups of three bases called codons. Translation begins at the first start codon (AUG, which codes for methionine) and continues until a stop codon (UAA, UAG, or UGA), which codes for no amino acid and ends the protein. Each codon maps to one amino acid via the genetic code below. The reading frame matters, shifting the start by one base changes every codon downstream.
Note: this tool reads the coding (sense) strand in the 5′→3′ direction and uses the standard genetic code. It translates the full sequence in the chosen frame; in real cells, ribosomes begin at the first AUG.
The genetic code (mRNA codons)
Related tools: Peptide charge & pI calculator · Amino acid quiz · Gene expression regulation explorer · Amino acid chart (all 20) · Codon chart (genetic code) · all biochem tools.
Worked example 1: the default sequence, frame 1
ATGGCCTTACATTGA, 15 bases, dividing evenly into 5 codons in frame 1.
The start codon falls right at the beginning here, so the full-frame translation and the "real" biological protein are the same thing: Met-Ala-Leu-His.
Worked example 2: finding the real ORF inside a longer frame
TTACGGATGAAACGTTAG in frame 1, the AUG isn't at the start this time, which is exactly the point of this example.
This tool shows every codon in the frame so you can see the whole picture, but a real ribosome ignores everything before the first AUG. Codons 1 and 2 (Leu, Arg) are shown for reference only. They're never actually part of the protein a cell would make from this reading frame.
FAQ
Why does the protein sometimes include amino acids before the start codon?
This tool translates the whole reading frame for reference, with AUG and stop codons flagged. A real ribosome only starts at the first AUG and ignores everything before it. See example 2 above.
Why do different reading frames give completely different proteins?
Codons are read in non-overlapping groups of three, so shifting the start by even one base regroups every downstream base into different codons. There are three reading frames per strand (six counting both strands), and usually only one is biologically real for a given gene.
Why is AUG both the start codon and the codon for methionine?
A special initiator tRNA recognizes the first AUG to kick off translation; any AUG appearing later in the frame is read normally and just inserts methionine into the middle of the chain like any other codon.
What's the difference between the coding strand and template strand?
The coding (sense) strand matches the mRNA sequence except T instead of U, what this tool expects as input. The template (antisense) strand is what RNA polymerase actually reads, and it's the reverse complement of the coding strand.
Practice problems
1. Translate ATGAAACCCTTTTAA in frame 1. What protein results?
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2. Translate GATGCATTAGCTAG starting in frame 2 (skip the first base). What's the real biological protein (starting only at the highlighted AUG)?
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See also: what happened to OligoCalc