Chapter 10: Biomolecules

Write two main functions of carbohydrates in plants.

Classify the following into monosaccharides and disaccharides. Ribose, 2-deoxyribose, maltose, galactose, fructose, and lactose.

What do you understand by the term glycosidic linkage?

What is glycogen? How is it different from starch?
Glycogen is an animal storage carbohydrate, more highly branched than starch.

• In animals, excess carbohydrates are stored as glycogen, which is highly branched.
• Starch, the plant storage carbohydrate, is made of two components: amylose (linear) and amylopectin (branched).
• Glycogen resembles amylopectin's structure but is even more branched.

What are the hydrolysis products of (i) sucrose and (ii) lactose?

What is the basic structural difference between starch and cellulose?
 Starch and cellulose are both carbohydrates but differ in structure and function.

• Starch is made of α-D-glucose units with two forms: amylose (linear) and amylopectin (branched).
• Cellulose is made of β-D-glucose units linked in straight chains with β-glycosidic bonds.
• Starch stores energy in plants; cellulose provides structural support to cell walls.

What happens when D-glucose is treated with the following reagents? (i) HI (ii) Bromine water (iii) HNO₃
D-glucose undergoes different reactions with each reagent, producing different products.

• (i) With HI: D-glucose is converted to n-hexane upon long heating.
• (ii) With bromine water: D-glucose forms gluconic acid.
• (iii) With nitric acid (HNO₃): D-glucose is oxidized to saccharic acid.

Enumerate the reactions of D-glucose which cannot be explained by its open-chain structure.
 Some behaviors of D-glucose (like different melting forms and reaction patterns) are not explained by its open-chain structure.

• D-glucose forms two crystalline forms (α and β) with different melting points, which isn't possible for a simple open-chain structure.
• Pentaacetate of glucose does not react with hydroxylamine, indicating the -CHO group is not free, which conflicts with the open-chain model.
• Reactions like Schiff’s test and 2,4-DNP test are not given by glucose, though they are by typical aldehydes.

What are essential and non-essential amino acids? Give two examples of each type.
Essential amino acids can't be made by the body and must come from diet; non-essential ones can be synthesized within.

• Essential amino acids: must be obtained from food—examples: leucine and valine.
• Non-essential amino acids: can be made by the body—examples: alanine and glycine.

Define the following as related to proteins (i) Peptide linkage (ii) Primary structure (iii) Denaturation.
These are three key terms explaining how proteins are structured and behave.

• (i) Peptide linkage: A bond formed by removing a water molecule between -COOH of one amino acid and -NH₂ of another.
• (ii) Primary structure: The precise order of amino acids in a protein chain; even a small change creates a new protein.
• (iii) Denaturation: Loss of protein shape and biological activity due to changes in temperature or pH, where secondary and tertiary structures break but the primary sequence stays unchanged.