text: what is the function of a stop codon?   a stop codon is a stop signal that terminates transcription. you might know that rna polymerase transcribes dna, for the purpose of protein synthesis. when the required gene is fully copied onto the rna transcript, it recognizes a stop signal when it reads the stop codon. that is when the transcription stops and the mrna transcript cuts off from the dna.  stop codon is very crucial because without a stop signal the whole dna would be transcribed, which is a great waste of time and cell energy.  i hope that helped....