Which of these is a stop codon in DNA?

The story behind the answer

TAA is a stop codon in DNA. In the coding strand of DNA, the three stop signals are TAA, TAG, and TGA; they correspond to UAA, UAG, and UGA in mRNA. These do not encode amino acids—instead, they recruit release factors that terminate translation and free the newly made protein. By contrast, ACT and ACA code for threonine, and GTA codes for valine.

Remember it this way: “TAA, TAG, TGA—stop today!” or the classic RNA mnemonic “U Are Annoying, U Are Gone, U Go Away” (UAA, UAG, UGA), then switch U→T for DNA. Historic names: ochre (TAA), amber (TAG), opal/umber (TGA).