Exposure to an extreme environment, such as high temperature, acidity or alkalinity, causes protein denaturation. Denaturation disrupts and destroys the secondary and tertiary structures of proteins, warping them from a normal alpha-helix and beta-sheet structure to a random shape.
Denaturation processes are generally too weak to break the peptide bonds keeping the backbone structure of the protein together, so they do not induce complete dissociation. The weak bonding interactions that hold secondary structures together, including hydrogen bonds and polar interactions, are destroyed in denaturation. Other weak interactions destroyed in these processes include salt bridges and disulfide bonds. Numerous reagents can attack these weak bonds and induce denaturation.
Heating a protein disrupts the hydrogen bonds and nonpolar interactions in the secondary protein structure by increasing the kinetic energy of the molecules to the point of bond dissociation. This heat-induced denaturation is observed in cooked eggs, whose whites and yolks denature and coagulate. Denaturizing proteins with heat makes their digestion easier by allowing enzymes to better access and break down the peptide chains during digestion. Denaturing bacterial proteins in an autoclave enables the sterilization of medical equipment.
Hydrogen bonding between secondary amide groups or side chains can also be disrupted by alcohols. The powerful denaturing properties of alcohols are what make them excellent antiseptics.