Which statement defines the start site for translation?

Which statement defines the start site for translation?

• A. The start codon AUG
• B. The stop codon UAA
• C. The poly-A tail
• D. The 5' cap

Answer: (A)

Translation begins at the start codon AUG on the mRNA, which defines the reading frame and specifies the first amino acid, methionine. The ribosome is recruited to the mRNA (often via the 5' cap in eukaryotes) and then scans until it encounters AUG in the proper context to start elongation. The other features don’t set the start site: the stop codon marks the end of translation, the poly-A tail relates to mRNA stability and translation efficiency rather than initiation, and while the 5' cap helps initiate ribosome binding, the actual starting point is the AUG codon itself.

Translation begins at the start codon AUG on the mRNA, which defines the reading frame and specifies the first amino acid, methionine. The ribosome is recruited to the mRNA (often via the 5' cap in eukaryotes) and then scans until it encounters AUG in the proper context to start elongation. The other features don’t set the start site: the stop codon marks the end of translation, the poly-A tail relates to mRNA stability and translation efficiency rather than initiation, and while the 5' cap helps initiate ribosome binding, the actual starting point is the AUG codon itself.