Question

Which of the following is/are examples of denaturation of protein?

• A. Coagulation of egg white
• B. Curdling of milk
• C. Clotting of blood
• D. Both (1) and (2)

Hint:

Denaturation of proteins can be caused by heat, acid, or mechanical agitation. This leads to a loss of their functional structure.

Answer 1

The Correct Option is D

To address the problem, we must identify which of the provided options represent protein denaturation.

1. Understanding Protein Denaturation:
Protein denaturation is the loss of a protein's native three-dimensional structure (secondary, tertiary, or quaternary). This occurs when non-covalent interactions (e.g., hydrogen bonds, hydrophobic interactions) or covalent bonds (e.g., disulfide bridges) are disrupted, but the primary peptide bonds remain intact. Common triggers include heat, pH variations, chemical agents, or mechanical stress.

2. Evaluating Option A (Coagulation of egg white):
The coagulation of egg white, observed during cooking, is induced by heat. Heat disrupts the hydrogen bonds and hydrophobic interactions within egg white proteins such as albumin, causing them to unfold and aggregate, transforming the liquid into a solid. This is a prime example of protein denaturation.

3. Evaluating Option B (Curdling of milk):
Milk curdles when an acid (e.g., lemon juice or vinegar) is introduced, lowering the pH. This modification of the charge on milk proteins like casein disrupts ionic and hydrogen bonds, leading to protein unfolding and aggregation into curds. This process also exemplifies protein denaturation.

4. Evaluating Option C (Clotting of blood):
Blood clotting is a physiological process wherein the enzyme thrombin converts soluble fibrinogen into insoluble fibrin. This forms a mesh that traps blood cells. This is a regulated, enzymatic event that does not involve the unfolding or structural loss of proteins due to external factors like heat or pH. Instead, it represents a functional alteration of protein structure, not denaturation.

5. Evaluating Option D (Both 1 and 2):
Option D encompasses both A (coagulation of egg white) and B (curdling of milk). As both A and B are instances of protein denaturation, and C is not, option D accurately identifies the denatured examples.

Final Answer:
The instances of protein denaturation are A (coagulation of egg white) and B (curdling of milk). Therefore, the correct option is D (Both 1 and 2).