Question

A short segment of an mRNA molecule is shown below. The polypeptide it codes for is also shown: 5'-AUGGUGCUGAAG : methionine-valine-leucine-lysine. A mutation in the DNA occurs so that the fourth base (counting from the 5 end) in the messenger RNA now reads A rather than G. What sequence of peptides will the mRNA now code for ______________.

Answer 1

The mutated mRNA sequence will code for the amino acid sequence methionine-cysteine-cysteine-glutamic acid.

Step-by-step explanation:

The original mRNA segment, 5'-AUGGUGCUGAAG, codes for the polypeptide methionine-valine-leucine-lysine. However, with the mutation where the fourth base of the mRNA sequence is now A instead of G, the new sequence will be 5'-AUGAUGCUGAAG.

This change in the mRNA sequence will result in a different amino acid sequence being coded for by the mRNA. To determine the new amino acid sequence, we need to refer to the genetic code chart.

Based on the genetic code, the codon AUG codes for methionine. So, the new sequence 5'-AUGAUGCUGAAG will still code for methionine as the first amino acid.

The next codon UGC codes for cysteine, the third codon UGU codes for cysteine again, and the last codon GAA codes for glutamic acid. Therefore, the new amino acid sequence coded for by the mutated mRNA is methionine-cysteine-cysteine-glutamic acid.