What happens at the molecular level during the denaturation of a globular protein by heating or extreme pH changes?

Answer and explanation

Correct answer: C. Higher structures unfold as non-covalent bonds break, but primary peptide sequence remains intact

  1. Step 1: Denaturation is the process in which a protein loses its native three-dimensional conformation and biological activity due to physical (heat) or chemical (pH, urea, organic solvents) stress.
  2. Step 2: Denaturation breaks relatively weak non-covalent interactions (hydrogen bonds, ionic bonds, hydrophobic interactions) that stabilize the folded secondary and tertiary structures, causing globular proteins to unfold into random coils.
  3. Step 3: Crucially, the strong covalent primary peptide bonds () linking amino acids together in sequence are not broken during denaturation.
  4. Step 4: Examples include the coagulation of egg white (albumin) upon boiling and the curdling of milk by lactic acid.
Answer
Secondary, tertiary, and quaternary structures are disrupted as non-covalent hydrogen bonds unfold, but the covalent primary peptide bond sequence remains intact
Why not the others: 'All covalent peptide bonds are completely hydrolyzed...' describes enzymatic or chemical proteolysis, not physical denaturation; 'Converted into inorganic hydrocarbon gas...' is false; 'Nitrogen atoms undergo nuclear transmutation...' is impossible in chemical systems.

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