DNA Sequence Analyzer
Paste any DNA sequence to instantly get nucleotide counts, GC content, the complementary strand, mRNA transcript, and codon-by-codon protein translation. No signup, runs entirely in your browser.
How to Use the DNA Sequence Analyzer
- 1Paste a DNA sequence using A, T, C, G (case-insensitive). Non-base characters are ignored automatically.
- 2Read the nucleotide counts and GC content — the percentage of G and C bases.
- 3Inspect the complementary strand and mRNA transcript generated by base-pairing rules.
- 4Follow the codon-by-codon translation from the first AUG to the stop codon.
Worked Example: From a Short Gene to a Peptide
Paste the coding sequence ATGGGCTAA. It has 9 bases: 4 are G or C, so GC content = 4/9 ≈ 44% — right in the 40–60% band used for reliable PCR primers. The complementary strand pairs each base (A↔T, G↔C): the analyzer returns TACCCGATT. Transcription swaps T for U in the message, giving the mRNA AUGGGCUAA.
Now split the mRNA into codons: AUG · GGC · UAA. AUG is the start codon and codes for methionine (Met); GGC codes for glycine (Gly); UAA is a stop codon, which ends translation without adding an amino acid. The resulting peptide is Met-Gly. This tiny example shows the whole central dogma in one screen — and why reading frame matters: delete the leading A and the codons regroup as TGG · GCT · AA, producing an entirely different, likely nonfunctional protein. That single-base shift is the essence of a frameshift mutation.
Molecular Biology Tips
GC content and stability
High GC content sequences are more stable due to the extra hydrogen bond in G-C pairs. PCR primers are typically designed to have 40-60% GC content to ensure reliable annealing.
Start and stop codons
Green AUG codons mark the translation start (methionine). Red Stop codons (UAA, UAG, UGA) terminate translation. In the tool, the first codon is assumed to be the start of the reading frame.
Reading frames
A sequence has three possible reading frames depending on where you start. The tool reads from position 1. If translation gives nonsense, try removing 1 or 2 leading bases to shift the reading frame.
Sequence direction
Enter your sequence 5′ to 3′ (left to right). The complement is shown 3′ to 5′ as it would appear on the antiparallel strand in a double helix.
Frequently Asked Questions
What format should I enter the DNA sequence in?
Enter the sequence using only the letters A, T, C, and G (case-insensitive). Spaces and non-ATCG characters are ignored. Enter the 5′ to 3′ template strand.
What is GC content and why does it matter?
GC content is the percentage of guanine and cytosine bases in a DNA sequence. G-C base pairs form 3 hydrogen bonds (vs 2 for A-T), making GC-rich regions more thermally stable. GC content above 60% indicates a high-melting-temperature sequence; below 40% indicates low stability.
How is the complementary strand generated?
Each base pairs with its complement: A pairs with T, T pairs with A, C pairs with G, and G pairs with C. The complement shown is the 3′ to 5′ strand (antiparallel to the template). To get the reverse complement (5′ to 3′ sense strand), reverse the output.
How does mRNA transcription work?
During transcription, RNA polymerase reads the DNA template and synthesises mRNA. Each T in the DNA is replaced by U in the mRNA (since RNA uses uracil instead of thymine). The mRNA sequence shown is the 5′ to 3′ message.
How is protein translation performed?
The mRNA is divided into codons (triplets of bases). Each codon maps to one amino acid using the standard genetic code. Translation starts at the first AUG (Met) codon and ends at a stop codon (UAA, UAG, or UGA). The tool translates from the beginning of the sequence.
Is my sequence stored?
No. All analysis runs locally in your browser. Your DNA sequence is never sent to any server.