What happens when egg white is boiled?

Egg white contains proteins (mainly albumin). On boiling, the protein gets denatured/coagulated.

What is denaturation?

Denaturation breaks the interactions responsible for higher levels of protein structure:

• Secondary structure: disrupted
• Tertiary structure: disrupted
• Quaternary structure: disrupted

However, the peptide bonds linking amino acids are not broken under ordinary boiling.

Which structure depends only on peptide bond sequence?

The primary structure is the linear sequence of amino acids in the polypeptide chain.

Since boiling does not hydrolyze peptide bonds, the primary structure remains intact.

Evaluate the options

• A: Quaternary $ightarrow$ destroyed during denaturation
• B: Primary $ightarrow$ remains intact
• C: Secondary $ightarrow$ destroyed during denaturation
• D: Tertiary $ightarrow$ destroyed during denaturation

Conclusion

The structure of protein that remains intact after coagulation of egg white on boiling is: $\boxed{\text{Primary structure}}$