Question

(a) Define 'Denatured Protein' with an example.

(b) What happens when glucose reacts with HCN ? Write the reaction involved.

(c) Name the disease caused by the deficiency of Vitamin C.

Hint:

Denaturation breaks the folded shape but not the primary structure. Glucose adds HCN at the CHO group to form a cyanohydrin. Lack of Vitamin C causes scurvy.

Answer 1

Step 1: Part (a), denatured protein:
A native protein has a fixed 3-D shape held by hydrogen bonds and other weak forces.
Heat, a change in pH, or certain chemicals break these bonds. The protein loses its secondary and tertiary structure, but the primary structure (the amino acid sequence) stays the same.
It also loses its biological activity. This changed protein is called a denatured protein.
Example: the white of an egg turns solid when the egg is boiled. The soluble globular albumin coagulates.

Step 2: Part (b), glucose with HCN:
Glucose has a free aldehyde group (-CHO). HCN adds across the C=O bond of this group, so glucose forms a cyanohydrin.
\[ \mathrm{HOCH_2(CHOH)_4CHO + HCN \rightarrow HOCH_2(CHOH)_4CH(OH)CN} \]
This reaction shows that glucose has a carbonyl group.

Step 3: Part (c), Vitamin C deficiency:
Vitamin C is ascorbic acid. Its lack causes scurvy, with bleeding gums and slow healing of wounds.

Final Answer:
(a) A protein that has lost its 3-D structure and activity on heating or a change in pH, for example boiled egg white. (b) Glucose cyanohydrin forms. (c) Scurvy. \[ \boxed{\text{(a) loss of 2}^{\circ}\text{ and 3}^{\circ}\text{ structure; (b) cyanohydrin; (c) scurvy}} \]