Why Might a Point Mutation in DNA Make a Difference

Question

Why might a point mutation in DNA make a difference in the level of protein's activity?
A) It might result in a chromosomal translocation.
B) It might exchange one stop codon for another stop codon.
C) It might exchange one serine codon for a different serine codon.
D) It might substitute an amino acid in the active site.
E) It might substitute the N-terminus of the polypeptide for the C-terminus.

Accepted Answer

A point mutation that substitutes an amino acid in the active site of a protein can alter the protein's activity because the active site is where the protein interacts with its substrates or other molecules to carry out its function. Even a small change in one amino acid can affect the shape and properties of the active site, making it less efficient or even nonfunctional. Choice A (chromosomal translocation) involves a large-scale rearrangement of genetic material and is unlikely to be caused by a single point mutation. Choice B (exchange of stop codons) and Choice C (exchange of synonymous codons) would not alter the protein sequence or activity. Choice E (substitution of N-terminus for C-terminus) would radically alter the protein structure and function.