what codons stop the making of a protein
Lesson Summary. Stop codons are sequences of DNA and RNA that are needed to stop translation or the making of proteins by stringing amino acids together. There are three RNA stop codons: UAG, UAA, and UGA. In DNA, the uracil (U) is replaced by thymine (T). If a change in the DNA sequence, or mutation, of a gene occurs that creates a stop codon, this is called a nonsense mutation.