[Campbell Biology P.537] According to the "MAKE CONNECTIONS" section and your understanding ... | Practice Question

According to the "MAKE CONNECTIONS" section and your understanding of molecular biology, which of the following best explains why a base-pair substitution in a coding region might have no effect on the amino acid sequence, or why an insertion in an exon might not affect the protein produced?

  • A: Degeneracy of the genetic code for substitution; insertion/deletion in multiples of three for insertion.
  • B: Substitutions only affect introns; insertions always occur in non-coding regions.
  • C: DNA repair mechanisms correct all substitutions; insertions are always excised during RNA splicing.
  • D: The protein can fold incorrectly to compensate; the cell can simply ignore the mutated region.

Explanation

The genetic code is degenerate, meaning multiple codons can specify the same amino acid. Therefore, a base-pair substitution might result in a new codon that still codes for the original amino acid, leading to no change in the protein. An insertion or deletion within an exon only causes a frameshift mutation and thus significant changes to the protein if the number of inserted or deleted nucleotides is not a multiple of three. If a segment of DNA in an exon that is a multiple of three is inserted or deleted, it will add or remove amino acids without changing the reading frame, potentially having no effect on protein function or producing a functional, albeit altered, protein.