Biology Genetics Practice Test

Which statement correctly describes the start codon usage in bacteria and eukaryotes?

AUG initiates translation in both; bacteria start with formylmethionine, eukaryotes with methionine. AUG is used only in bacteria; eukaryotes use GUG. UAA initiates translation in bacteria; AUG in eukaryotes. GGC initiates translation in both.

Correct Answer:

AUG initiates translation in both; bacteria start with formylmethionine, eukaryotes with methionine.

Explanation:

Start codon use centers on how translation begins and which amino acid starts the polypeptide. AUG signals the start in both bacteria and eukaryotes, so translation begins at AUG in either domain. The initiating amino acid differs: in bacteria the initiator tRNA brings formylmethionine, so the first residue is formylmethionine; in eukaryotes the initiator tRNA brings methionine, which is usually not formylated and is often removed later in the process. While bacteria can occasionally use alternative start codons like GUG or UUG, AUG remains the standard start. The other options misstate which codons initiate translation or what amino acid starts the chain (for example, UAA is a stop codon, not a start signal).

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