![]() AUG is also known as a start codon, as it initiates the process of translation.If this is a mutation as a stop codon and its finishes prematurely it is called an amber codon. Three codons, UAA, UAG, and UGA, are known as stop codons as they stop the process of translation.The genetic code is universal because it is the same among all organisms.Every three nucleotides in the genetic code corresponds to one codon, which can either encode an amino acid or a stop signal for translation.Practice Exam 4 B/B Section Passage 10 Question 54 Sample Test B/B Section Passage 4 Question 21 These codons are similar in all organisms and thus are considered universal. Out of these 61 codons, the codon AUG (which encodes the amino acid methionine) also serves as a the start signal ( start codon) for translation initiation. ![]() The remaining 61 codons encode 20 amino acids. Three of these codons are stop codons: UAA, UAG, and UGA. There are 64 possible nucleotide triplets (4 possible nucleotides in groups of three = 4 3), which is far more than the number of amino acids. ![]() Thus, the genetic code is degenerate, meaning many amino acids that are encoded by a few different codons. You’ll see that many amino acids are actually encoded by more than one codon. Take a look at the chart below showing which codons encode which amino acids. Mutations can also have wider impacts upon translation and transcription. If there is a mutation which occurs and causes an early stop codon in an mRNA sequence this is called an amber codon. There is also a stop codon present, which signals the end of translation and synthesis of the polypeptide chain. In the example below, a short polypeptide of three amino acids is encoded by nine RNA nucleotides. Every three nucleotides in the RNA sequence is “read” as a separate codon, which encodes a specific amino acid this is why codons are known as the “triplet code”. Each three nucleotides (triplet) in the genetic code, known as a codon, encodes a specific amino acid or stop signal.Īfter DNA is transcribed into RNA, the RNA is translated into a polypeptide sequence.
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