During denaturation of proteins, which of the following bond/ interaction is not broken?

Peptide bonds

The correct answer is option 4. Peptide bonds.

Here is a detailed explanation of how each type of bond or interaction is affected during protein denaturation:

1. Electrostatic Attraction

Electrostatic attractions, also known as ionic bonds, occur between positively and negatively charged side chains of amino acids. These interactions contribute to the stabilization of the protein's tertiary and quaternary structures.

Effect of Denaturation: During denaturation, the protein structure unfolds, which disrupts these electrostatic interactions. This is often due to changes in the environment, such as alterations in pH or ionic strength, which affect the charge distribution and thereby weaken or break these ionic bonds.

2. Hydrogen Bonds

Hydrogen bonds are non-covalent interactions that form between hydrogen atoms attached to electronegative atoms (like oxygen or nitrogen) and other electronegative atoms. These bonds help stabilize the secondary structures (α-helices and β-sheets) and contribute to the overall tertiary structure of proteins.

Effect of Denaturation: Denaturation involves the disruption of the protein's three-dimensional structure, which breaks the hydrogen bonds that stabilize these structures. For example, when a protein is exposed to high temperatures or harsh chemicals, the hydrogen bonds are disrupted, leading to the unfolding of the protein.

3. Disulphide Bonds

Disulphide bonds are covalent bonds formed between the sulfur atoms of two cysteine residues in a protein. They play a crucial role in stabilizing the tertiary and quaternary structures of proteins.

Effect of Denaturation: Disulphide bonds are generally more resistant to denaturation compared to non-covalent interactions. However, they can still be disrupted, especially by strong reducing agents that break these covalent bonds. During denaturation, if the conditions are severe (e.g., reducing agents or high temperatures), disulphide bonds can be broken, leading to further destabilization of the protein structure.

4. Peptide Bonds

Peptide bonds are covalent bonds that link amino acids together in the primary structure of proteins. Each amino acid is connected to the next by a peptide bond, forming the backbone of the protein chain.

Effect of Denaturation: Peptide bonds are not affected during denaturation. Denaturation primarily affects the higher-order structures of the protein (secondary, tertiary, and quaternary) but does not break the covalent peptide bonds that hold the amino acids in sequence. The primary structure of the protein remains intact, but the overall three-dimensional structure is disrupted.

Summary

Electrostatic attractions and hydrogen bonds are disrupted during denaturation due to the loss of the protein's three-dimensional structure.

Disulphide bonds can also be affected by denaturation, especially under harsh conditions that break covalent bonds.

Peptide bonds are not broken during denaturation, as they are responsible for maintaining the primary structure of the protein.

Thus, the bond or interaction that is not broken during the denaturation of proteins is peptide bonds.