Q.On boiling egg albumin becomes opaque white.

Step 1. Egg albumin is a globular protein (section 14.3.3a), normally folded compactly with hydrophobic side chains buried in its interior and polar side chains exposed on its water-facing surface -- this arrangement is why raw egg white is a clear, water-soluble liquid.

Step 2. Boiling supplies enough thermal energy to disrupt the non-covalent interactions (hydrogen bonds, electrostatic attractions, dispersion forces) that hold albumin's specific secondary/tertiary folded shape together -- this is denaturation (section 14.3.5); crucially, the covalent peptide bonds of the primary structure are NOT broken.

Step 3. As the protein unfolds, its previously-buried hydrophobic interior becomes exposed to the surrounding water (Do you know box, section 14.3.5); the unfolded chains, no longer individually water-soluble, aggregate together and coagulate. …

Identify the physical change (clear liquid to opaque white solid) as protein denaturation caused by heat, and explain it via loss of non-covalent folding forces, hydrophobi …

• Claiming that boiling 'breaks down' or chemically decomposes the protein (e.g. hydrolyses its peptide bonds); denaturation specifically leaves the primary sequence intact. …