Protein denaturation example — In a hard boiled egg, which structural level of ovalbumin is least affected by denaturation?

Introduction:
Cooking an egg is a classic demonstration of protein denaturation. Heat disrupts weak interactions, leading to loss of native structure and aggregation. This question asks which level of protein structure remains least affected under such conditions for the major egg white protein, ovalbumin.

Given Data / Assumptions:

• Ovalbumin is heated to the point of irreversible denaturation in a hard boiled egg.
• No proteolysis or peptide bond hydrolysis is implied by normal cooking times.
• Denaturation refers to loss of native secondary, tertiary, and quaternary organization.

Concept / Approach:
Primary structure is the linear amino acid sequence linked by peptide bonds. Heat denaturation primarily disrupts noncovalent forces (hydrogen bonds, hydrophobic interactions, ionic pairs) and can break some disulfide arrangements but generally does not cleave peptide bonds. Therefore, the amino acid sequence remains largely intact, while higher order structures are altered.

Step-by-Step Solution:

Verification / Alternative check:
Electrophoresis after cooking shows bands corresponding to intact polypeptide mass unless deliberate hydrolysis is performed. Functional assays lose activity, confirming higher order structural loss despite preserved sequence.

Why Other Options Are Wrong:

• Secondary and tertiary: these are the first to change during denaturation.
• Quaternary: inter subunit arrangements or aggregation are affected by heat.
• All equally affected: different levels respond differently; covalent backbones are most resistant.

Common Pitfalls:
Equating denaturation with chemical degradation. Denaturation is not the same as hydrolysis; it is a loss of native conformation without necessarily breaking the peptide chain.

Final Answer:
The primary structure of ovalbumin.