What Is a Stop Codon?

1. A triplet base sequence of a messenger ribonucleic acid (mRNA) that stops peptide chain synthesis during protein translation. 2. A codon that functions as a signal to terminate protein synthesis during mRNA translation. 3. Codons in mRNA molecules that stop protein synthesis.

Stop code: UAG, UAA, UGA are stop codons. The corresponding stop codon sequences on the DNA are TAG, TAA, TGA.

Stop codons are also called "meaningless codons." Codons that do not encode any amino acids, such as UAA, UAG and UGA. When the peptide chain is extended to one of the three codons, it stops immediately, so that the synthesized polypeptide chain is released. Therefore, the stop codon is regarded as a stop signal ^.

Yanofsky was studying in 1964

Their experimental method is not

Until 1965, Weigert, M. and Ggaren, A replaced the amino acid at the tryptophan site in the alkaline phosphatase gene to prove that the base composition of the nonsense codon in E. coli revealed amber and ochre mutant genes They are stop codons UAG and UAA. At that time, 61 of the 64 ciphers were deciphered, leaving only UAA, UAG, and UGA to be determined. Garen et al. Used a similar strategy to Brenner to identify nonsense codons. They isolated a large number of back mutants from a nonsense mutant strain in the alkaline phosphatase gene (pho A) of E. coli, and then explored each nonsense mutation in the peptide equivalent to the returned non What is the amino acid at the sense codon position? It can be seen that the nonsense codon is generated from the codon at the tryptophan site of the gene. In the back mutation, the nonsense codon becomes the corresponding codon for Trp, Ser, Tyr, Leu, Glu, Gln, and Lys. Only the URG of Trp becomes UAG, and then based on this mutation back to 7 amino acids, so the nonsense mutation codon produced by Trp is UAG. In 1967 Brennr and Crick proved that UGA was the third nonsense codon. According to the three nicknames of nonsense mutations, the three stop codons UAA are called ochre codons (corresponding to ocher mutations); UAG is called amber codons (corresponding to amber mutations); UGA is called opal codons ( (Corresponds to opal mutation).

Recent studies have found that the genetic code used by mitochondria and chloroplasts is slightly different. There are four stop codons for mitochondria and chloroplasts, which are UAA, UAG, AGA, and AGG.