Amino Acid Mutation Question

[Mariolee]

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The question I encountered asks about which kind of mutation happened that would make cause a lack of 50 amino acids near the C terminus. The possible answers were

missense mutation
back mutation
a sense mutation
frameshift mutation

The answer was frameshift mutation because the addition or deletion of a base could lead to creation of stop codon causing deletion of the 50 amino acids in the chain. However, why could it not be a missense mutation? Can't the missense cause one amino acid to become a stop codon instead?

 

[aldol16]

The answer was frameshift mutation because the addition or deletion of a base could lead to creation of stop codon causing deletion of the 50 amino acids in the chain. However, why could it not be a missense mutation? Can't the missense cause one amino acid to become a stop codon instead?

That's more specifically called a nonsense mutation. "Missense" refers to the "wrong" sense, or the wrong amino acid substituted for the correct one. "Nonsense" refers to "no" sense because the stop codon does not code for an amino acid.

 

[NextStepTutor_3]

Yes good answer! Careful word choice is important. It's similar to the idea that you wouldn't call two enantiomers diastereomers - since diastereomers are particularly specified as "stereoisomers that aren't enantiomers." A missense mutation is the substitution of one amino acid for another, not the substitution of a stop codon for an amino acid. The two types of mutation don't overlap.