Q1(e). Permanent and temporary denaturation of a protein

Answer in brief

Denaturation is loss of native 2°, 3° and 4° structure and of activity with peptide bonds intact; temporary denaturation reverses when the agent is removed, permanent does not.

Key points

• Temporary (reversible): mild agents such as urea, guanidinium chloride, gentle warming, small pH change; chain unfolds but stays soluble.
• Permanent (irreversible): boiling, strong acid or alkali, Hg²⁺, Pb²⁺, Ag⁺, alcohol, UV; chains aggregate, wrong S–S bridges, coagulation.
• Example: ribonuclease A in 8 M urea + β-mercaptoethanol is active again after dialysis.
• Example: boiled egg white (albumin); curdling of milk (casein).
• Renaturation (Anfinsen, RNase A): the 1° sequence alone fixes the 3-D fold.