What is the start codon?

What is the start codon?

• A. AUG
• B. UAA
• C. UGG
• D. UAG

Answer: (A)

Starting translation relies on a signal that marks where to begin reading the mRNA. The start codon is AUG, which sets the reading frame and encodes the amino acid methionine (in bacteria, the initiator tRNA brings formyl-methionine). This AUG signal tells the ribosome to start building the protein from that point. Other options are not start signals: UAA and UAG are stop codons that terminate translation, and UGG codes for the amino acid tryptophan but is not a start codon. (Note: while AUG is the canonical start codon in most organisms, some organisms can use rare non-AUG starts, but AUG remains the primary signal.)

Starting translation relies on a signal that marks where to begin reading the mRNA. The start codon is AUG, which sets the reading frame and encodes the amino acid methionine (in bacteria, the initiator tRNA brings formyl-methionine). This AUG signal tells the ribosome to start building the protein from that point. Other options are not start signals: UAA and UAG are stop codons that terminate translation, and UGG codes for the amino acid tryptophan but is not a start codon. (Note: while AUG is the canonical start codon in most organisms, some organisms can use rare non-AUG starts, but AUG remains the primary signal.)