Which of the following genetic codons acts as both an initiation codon for translation and codes for the amino acid Methionine?
Answer and explanation
Correct answer: A. AUG
- Step 1: Translation initiation requires a designated start codon situated on the messenger RNA sequence.
- Step 2: The ribonucleotide triplet AUG serves a dual function: it specifies the initiation site for polypeptide synthesis and directs the incorporation of methionine (formyl-methionine in prokaryotes).
- Step 3: The codons UAA, UAG, and UGA function exclusively as nonsense (stop) signals that trigger chain termination.
Answer
AUG.
Why not the others: UAA (ochre) is a nonsense stop codon that terminates translation without encoding any amino acid; UAG (amber) is a nonsense stop codon that signals release factor binding; UGA (opal) is a nonsense stop codon terminating polypeptide chain elongation.
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