Question

What is the effect of denaturation on the structure of proteins ? What are the common types of secondary structures of proteins ?

Hint:

Denaturation breaks hydrogen bonds, so secondary and tertiary structure are lost while the primary structure remains. The secondary structures are the alpha-helix and the beta-pleated sheet.

Answer 1

Step 1: What is denaturation?
Denaturation is the loss of the biological activity of a protein when it is heated or treated with acid, alkali or alcohol.
The protein is changed from its native, working form into a different form.

Step 2: Effect on structure.
The hydrogen bonds that hold the secondary and tertiary structures are broken. So the globular protein unfolds and the helix uncoils.
The primary structure (the order of amino acids) stays the same, because peptide bonds are not broken.
Because the folded shape is lost, the protein loses its biological activity. An example is the coagulation of egg white on boiling.

Step 3: Types of secondary structure.
There are two common types.
1. \( \alpha \)-helix: the chain is coiled into a right-handed spiral, held by hydrogen bonds between the C=O of one amino acid and the N-H of the fourth amino acid after it.
2. \( \beta \)-pleated sheet: chains lie side by side in a zig-zag sheet and are joined by hydrogen bonds between neighbouring chains.

Final Answer:
Denaturation destroys the secondary and tertiary structures (primary stays) and the protein loses activity. The secondary structures are the \( \alpha \)-helix and the \( \beta \)-pleated sheet.