Question

(a) Define the following terms :

(i) Denaturation as related to proteins

(ii) Oligosaccharides

(b) On the basis of structure differentiate between Amylose and Amylopectin.

Hint:

Denaturation destroys the secondary and tertiary structure only. Amylose is linear with C1-C4 links, amylopectin is branched with extra C1-C6 links.

Answer 1

Step 1: Understanding the Concept:
This question tests three ideas from the chapter on Biomolecules: protein structure, the classification of carbohydrates, and the two components of starch.
A protein has four levels of structure. The primary structure is the amino acid sequence. The secondary and tertiary structures are the folds held by hydrogen bonds and other weak forces.

Step 2: Define denaturation, part (a)(i).
Denaturation is the loss of the secondary and tertiary structure of a protein, while the primary structure stays the same.
It happens when the weak hydrogen bonds and other interactions break. Heat, a change in pH, or chemicals such as urea can cause it.
The protein unfolds and loses its biological activity. For example, the white of an egg turns solid and white when boiled, because the egg albumin is coagulated.

Step 3: Define oligosaccharides, part (a)(ii).
Oligosaccharides are carbohydrates that give two to ten monosaccharide units on hydrolysis.
The units are joined by glycosidic linkages. They are named by the number of units: disaccharides, trisaccharides and so on.
For example, sucrose is a disaccharide. It gives one glucose and one fructose unit on hydrolysis.

Step 4: Differentiate Amylose and Amylopectin, part (b).
Both are polysaccharides present in starch, and both are built from \(\alpha\)-D-glucose units. They differ in how the chain is built.
Amylose: It is a long, unbranched (linear) chain. The glucose units are joined only by \(\alpha\)-glycosidic links between C1 and C4. It forms about 15-20% of starch and is water soluble.
Amylopectin: It is a branched chain polymer. The main chain has C1-C4 \(\alpha\)-links, and the branches start through C1-C6 \(\alpha\)-links. It forms about 80-85% of starch and is insoluble in water.

Final Answer:
Denaturation is the loss of the secondary and tertiary structure of a protein with the primary structure intact. Oligosaccharides give 2 to 10 monosaccharide units on hydrolysis. Amylose is linear (C1-C4 links only) and amylopectin is branched (C1-C4 and C1-C6 links).