The stop codon is the codon that codes for the stoppage of protein synthesis. That is the production of new proteins should stop. There are 3 STOP codons in the genetic code - UAG, UAA, and UGA. These codons signal the end of the polypeptide chain during translation. These codons are also known as nonsense codons or termination codons as they do not code for an amino acid. A stop codon is a genetic code that signals the end of protein manufacturing inside the cell, like a period at the end of a sentence.