During the denaturation of proteins, which of these structures will remain intact?

Solution

Chemistry ma’am · 3 steps

Ask which bonds the heat or acid actually breaks. Peptide bonds are covalent, so they survive.

1. What denaturation does. Heat, a change in pH or strong salts disturb the weak forces that hold a protein in its folded shape. The globules unfold and the helices uncoil, so the protein loses its biological activity.

   Structure	Held together by	During denaturation
   Primary	covalent peptide bonds, -CO-NH⁻	intact: these bonds are strong and do not break
   Secondary	hydrogen bonds between C=O and N-H groups	lost: the α-helix and β-sheet open up
   Tertiary	hydrogen bonds, disulphide links, van der Waals and ionic forces	lost: the overall folding is undone
   Quaternary	the same forces, acting between subunits	lost: the subunits come apart

2. Why primary survives. The primary structure is only the sequence of amino acids, joined by covalent peptide bonds. Denaturation does not hydrolyse these bonds, so the sequence stays the same.
3. So. Only the primary structure remains intact, which is option (a). A boiled egg white is a good example: it sets, but its protein chains still have the same sequence.

The idea to keep. Denaturation breaks the weak forces, not the peptide bonds. So the shape is lost, but the amino acid sequence, which is the primary structure, stays the same.

Answer from the NTA final answer key. Solution by PrepWiser.