Globular proteins are typically constructed from several layers of secondary structures, with a hydrophobic core and a hydrophilic surface. Is this true for fibrous proteins such as keratin? Explain. You are performing site-directed mutagenesis to test predictions about which residues are essential for protein function. Which of each pair of amino acid substitutions listed below would you expect to disrupt protein structure the most? Explain. Val replaced by Ala or Phe. Lys replaced by Asp or Arg. Gln replaced by Glu or Asn. Pro replaced by His or Gly. Protein denaturation can be triggered by a variety of environmental insults, including high temperature, covalent modification, and oxidation. Explain why researchers have observed a correlation between the level of heat shock proteins and the ratio of oxidized to reduced glutathione in cells subjected to oxidative stress.