Question

A bacterial protein is encoded by the following mRNA sequence 5 AUGGUGCUCAUGCCCTAA-3: The second methionine codon (AUG) in

this mRNA sequence will
A. serve as the initiation codon
B. encode N-formylmethionine
C. encode methionine that will eventually be removed
D. encode unformylated methionine

Answer 1

The second methionine codon (AUG) in an mRNA sequence encodes for unformylated methionine, which will be incorporated into the growing polypeptide chain.

Step-by-step explanation:

The second methionine codon (AUG) in an mRNA sequence will encode unformylated methionine. In prokaryotes, the initiator tRNA carries a formylated methionine (fMet) that is used to start the synthesis of a polypeptide chain. However, if an AUG codon appears after the initiation site, it codes for the incorporation of a regular, unformylated methionine into the growing polypeptide chain. In eukaryotes, the initiating methionine coded by AUG is also not formylated. The consensus sequence around the AUG, according to Kozak's rules, helps determine the efficiency of translation initiation in eukaryotes, but all subsequent AUG codons simply code for the addition of unformylated methionine into the polypeptide.