You are performing site-directed mutagenesis to test predictions about which residues are essential for a protein's function. Which of each pair of amino acid substitutions listed below would you expect to disrupt protein structure the most? Explain.
(a) Val replaced by Ala or Phe.
(b) Lys replaced by Asp or Arg.
(c) Gln replaced by Glu or Asn.
(d) Pro replaced by His or Gly.