Answer:
d. Lysine is replaced by tryptophan (nonpolar)
Explanation:
Amino acid substitutions can have varying affects on the protein function, depending on the specific substitution and the location of the substitution.
If the substitution occurs in an important region, for example an enzyme active site, then the function of the protein could be destroyed.
Additionally, if the substitution replaces the amino acid with a highly different amino acid with different properties (eg. polarity), it could alter the structure and function of the protein.
Replacing lysine (polar) with a tryptophan (non-polar) changes the properties of the amino acid at that location, whereas the other substitutions do not.
