Transcription and translation

How the transcription translation tool works

The transcription translation tool takes a raw DNA sequence and converts it into a chain of amino acids. You paste a DNA sequence into the calculator, and the tool first transcribes it into messenger RNA (mRNA). It then translates that mRNA sequence into a protein sequence using the standard genetic code. The output shows you the exact mRNA string and the corresponding protein chain.

The science behind transcription

The central dogma of molecular biology explains how information flows from DNA to RNA to protein. Transcription is the first step. An enzyme called RNA polymerase reads one strand of DNA and builds a complementary mRNA strand. The rules are simple. Cytosine pairs with guanine, and adenine pairs with thymine. However, RNA uses a base called uracil instead of thymine. When the enzyme encounters an adenine on the DNA strand, it adds a uracil to the growing mRNA strand. This mRNA strand carries the genetic blueprint out of the nucleus to the ribosome.

Translation and reading frames

Translation happens at the ribosome. The ribosome reads the mRNA sequence in chunks of three bases. These three-letter chunks are codons. The transcription translation tool reads your sequence one codon at a time to build the final protein. Translation almost always starts at a specific start codon, AUG, which also codes for the amino acid methionine. The ribosome continues reading the sequence, adding amino acids until it hits a stop codon (UAA, UAG, or UGA). Stop codons do not code for an amino acid. They tell the ribosome to release the finished protein chain.

The starting point for reading the codons matters. Because codons are three bases long, a ribosome can read any given sequence in three different ways depending on where it starts. These are reading frames. If the ribosome shifts by just one base, the entire sequence of codons changes. This usually results in a completely different and nonfunctional protein. The tool defaults to the first reading frame, but you can shift the frame to see how the resulting protein changes.

What the calculator leaves out

This tool uses the standard genetic code shared by most plants, animals, and bacteria. It does not account for alternative genetic codes. For example, human mitochondrial DNA uses a slightly different code where the codon UGA codes for tryptophan instead of acting as a stop signal. The calculator also ignores post-translational modifications. Real proteins often fold into complex 3D structures and undergo chemical changes after translation, which this simple sequence converter cannot predict.