Lesson Plan: Biomolecules

Organic Chemistry (Class 12)

Biomolecules

Where Chemistry meets Biology. This chapter covers the chemical basis of life: Carbohydrates (Energy), Proteins (Structure/Enzymes), Vitamins (Regulators), and Nucleic Acids (Information). Focus on the Cyclic Structure of Glucose and Peptide bonds.

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⚠️ Prerequisites

Stereochemistry: D/L configuration (relative to Glyceraldehyde) vs d/l (optical rotation).
Functional Groups: Reactions of Aldehydes (oxidation) and Alcohols (acetylation).
Amides: Formation of amide bond (Peptide linkage).

🧠 Study Approach

Structure is Everything: Don't just read about Glucose; draw the Fischer projection and the Haworth projection. Understand why Glucose forms a hemiacetal ring (C1 attacks C5-OH).

Study Sequence

1. Carbohydrates Classification

Monosaccharides, Oligosaccharides, Polysaccharides.
Reducing vs Non-Reducing Sugars: Presence of free -CHO or -C=O group (Tollens'/Fehling's test).

2. Structure of Glucose (CRITICAL)

Reactions proving structure: HI (n-hexane), Bromine water (Gluconic acid), $HNO_3$ (Saccharic acid), Acetic anhydride (Pentaacetate).
Cyclic Structure: $\alpha$-D-Glucose and $\beta$-D-Glucose (Anomers). Mutarotation.

3. Disaccharides & Polysaccharides

Glycosidic Linkage: Formation of ether bond by water loss.
Sucrose: Invert sugar (Hydrolysis changes rotation). Non-reducing.
Maltose/Lactose: Reducing.
Starch vs Cellulose vs Glycogen: Amylose vs Amylopectin.

4. Amino Acids (Proteins)

Essential vs Non-Essential. Zwitterion formation (Amphoteric nature). Isoelectric point.
Peptide Linkage: $-CO-NH-$ bond formation.

5. Structure of Proteins

Primary: Sequence of amino acids.
Secondary: $\alpha$-Helix (H-bonds) and $\beta$-Pleated sheet.
Tertiary/Quaternary: 3D folding (Disulphide bonds, Van der Waals).
Denaturation: Loss of biological activity (2°, 3° structure destroyed, 1° remains).

6. Vitamins

Fat Soluble: A, D, E, K (Stored in liver/adipose).
Water Soluble: B, C (Excreted in urine, need daily intake). Exception: B12.
Deficiency diseases (Night blindness, Scurvy, Rickets, Beri-Beri, Anaemia).

7. Nucleic Acids (DNA/RNA)

Components: Sugar (Ribose/Deoxyribose) + Base (AGCT/U) + Phosphate.
Nucleoside vs Nucleotide: Nucleoside = Sugar + Base. Nucleotide = Nucleoside + Phosphate.
Linkage: Phosphodiester linkage (backbone).
DNA Structure: Double helix, AT (2 H-bonds), GC (3 H-bonds).

🎯 How to Practice

Drawing Practice: Draw D-Glucose (Open chain), then cyclize it to $\alpha$-D-Glucopyranose. Memorize the positions of OH groups (Right-Left-Right-Right).

Linkage Logic: Differentiate linkages:
Peptide: $C-N$
Glycosidic: $C-O-C$
Phosphodiester: $P-O-C$.

Disease Table: Create a simple table: Vitamin | Name | Deficiency Disease. Memorize it. (e.g., Vit C - Ascorbic Acid - Scurvy).

📝 Quick Revision Notes

Glucose Reactions Proving Structure

HI $\to$ n-Hexane (Straight chain)
$NH_2OH$ $\to$ Oxime (Carbonyl group)
$Br_2/H_2O$ $\to$ Gluconic Acid (Aldehyde group)
$HNO_3$ $\to$ Saccharic Acid (Primary alcohol)

DNA Bases

Purines: Adenine (A), Guanine (G)
Pyrimidines: Cytosine (C), Thymine (T) (Uracil in RNA)
Pairing: A=T, G$\equiv$C

Zwitterion

$H_3N^+-CH(R)-COO^-$
( dipolar ion, neutral overall )

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