On boiling the egg, what structural changes are taking place in the egg white ?

Options

A. The colour of the egg changes from colourless to white.
B. `2^(@)` and `3^(@)` structures are destroyed but `1^(@)` structure remains intact.
C. `1^(@),2^(@)and 3^(@)` structures of egg are destroyed.
D. A reversible change takes place which can be reversed by decreasing the temperature .

Explanation

### Step-by-Step Solution:

1. **Understanding the Composition of Egg White**:
- Egg white primarily consists of water and proteins, with the main protein being albumin.

2. **Protein Structure Levels**:
- Proteins have four levels of structure: primary (1°), secondary (2°), tertiary (3°), and quaternary (4°).
- In the case of egg white, the proteins are primarily in the secondary (2°) and tertiary (3°) structures.

3. **Effect of Boiling**:
- When an egg is boiled, the heat causes the proteins to denature. This means that the secondary and tertiary structures of the proteins are disrupted.
- The heating process breaks the non-covalent interactions (like hydrogen bonds, ionic bonds, and Van der Waals forces) that maintain the 2° and 3° structures.

4. **Conversion to Primary Structure**:
- As the proteins denature, they unfold and lose their 2° and 3° structures, resulting in a linear chain of amino acids, which represents the primary (1°) structure.
- The peptide bonds that link the amino acids remain intact during this process.

5. **Resulting Changes**:
- The denaturation of proteins leads to a change in the physical properties of the egg white, such as its color and texture. The egg white changes from a transparent liquid to a white, opaque solid.

6. **Irreversibility of the Process**:
- The denaturation process is generally irreversible; once the proteins have denatured and formed the solid structure, they cannot revert back to their original 2° and 3° structures.

### Conclusion:
- The boiling of an egg leads to the denaturation of the proteins in the egg white, resulting in the conversion of the 2° and 3° structures to a 1° structure, while the peptide bonds remain intact. This process is irreversible.