Which codon signals the start of translation?

Which codon signals the start of translation?

• A. AUG
• B. UAA
• C. UGA
• D. UAG

Answer: (A)

Translation begins at a specific codon that signals the ribosome to start assembling the protein, and that codon is AUG. It not only codes for methionine (the amino acid used to start a polypeptide in both bacteria and eukaryotes) but also serves as the binding site for the initiator tRNA. Once this tRNA pairs with AUG, the ribosome is positioned in the correct reading frame and can begin elongation with the remaining codons. The other codons listed are stop signals (UAA, UAG, UGA) that tell the ribosome to terminate translation rather than start it. In bacteria, initiation is helped by the Shine-Dalgarno sequence to position AUG correctly relative to the ribosome, while in eukaryotes the ribosome typically finds AUG by scanning from the 5' cap and recognizing a favorable Kozak context. So AUG is the start codon signaling the start of translation.

Translation begins at a specific codon that signals the ribosome to start assembling the protein, and that codon is AUG. It not only codes for methionine (the amino acid used to start a polypeptide in both bacteria and eukaryotes) but also serves as the binding site for the initiator tRNA. Once this tRNA pairs with AUG, the ribosome is positioned in the correct reading frame and can begin elongation with the remaining codons. The other codons listed are stop signals (UAA, UAG, UGA) that tell the ribosome to terminate translation rather than start it. In bacteria, initiation is helped by the Shine-Dalgarno sequence to position AUG correctly relative to the ribosome, while in eukaryotes the ribosome typically finds AUG by scanning from the 5' cap and recognizing a favorable Kozak context. So AUG is the start codon signaling the start of translation.