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​Stop Codon

updated: May 10, 2022


A stop codon is a sequence of three nucleotides (a trinucleotide) in DNA or messenger RNA (mRNA) that signals a halt to protein synthesis in the cell. There are 64 different trinucleotide codons: 61 specify amino acids and 3 are stop codons (i.e., UAA, UAG and UGA).



Stop codon. A stop codon is to protein synthesis what a period is to a sentence. Since a protein isn't infinitely long, biology created an incredibly clever way to say, “Stop! You've reached the end of this protein.”

Prabarna Ganguly
Prabarna Ganguly, Ph.D.

Science Writer/Editor

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