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High Yield Topic

Biomolecules

Chemistry Unit 14
25 min read
IAT Advanced
Hot Topic

1. Core Concept

Biomolecules are the organic building blocks of life. They range from simple sugars to massive polymers (proteins, DNA) that regulate biological processes through specific structural recognition.

2. Carbohydrates

  • Classification: Monosaccharides (Glucose, Fructose), Disaccharides (Sucrose, Lactose, Maltose), Polysaccharides (Starch, Cellulose, Glycogen).
  • Glucose Structure: Contains an aldehyde group and 5 -OH groups. Forms a 6-membered pyranose ring.
  • Fructose Structure: Forms a 5-membered furanose ring.
  • Glycosidic Linkage: Bond holding two monosaccharides together (e.g., in Sucrose: C1 of Glucose and C2 of Fructose).
  • Reducing Sugars: Any carbohydrate that reduces Tollens' or Fehling's reagent (all monosaccharides, most disaccharides except Sucrose).

3. Proteins

Building Blocks: Amino acids (R-CH(NH2)-COOH).

Zwitterion: At isoelectric point, amino acids exist as H3N+-CH(R)-COO-.

Peptide Bond: -CONH- link between amino acids.

Structure Levels:

  • Primary: Sequence of amino acids.
  • Secondary: α-helix or β-pleated sheets (H-bonding).
  • Tertiary: 3D folding (Active form).
  • Quaternary: Interaction between multiple polypeptide chains (e.g., Hemoglobin).

Denaturation: Loss of biological activity due to change in pH or temperature (destroys secondary/tertiary structure, keeps primary intact).

4. Enzymes & Vitamins

Enzymes:

Usually globular proteins acting as biological catalysts (Lock and Key model) by significantly lowering activation energy.

Vitamins:

  • Fat Soluble: A, D, E, K (stored in liver/adipose tissue).
  • Water Soluble: B-complex, C (supplied regularly).

Deficiencies: A (Night blindness), B1 (Beri-beri), C (Scurvy), D (Rickets), K (Blood clotting failure).

5. Nucleic Acids

Components: Sugar (Ribose/Deoxyribose) + Phosphate + Nitrogen Base (Purines: A, G; Pyrimidines: C, T, U).

  • DNA: Double helix, A=T, G≡C. Sugar: Deoxyribose.
  • RNA: Single-stranded, A=U, G≡C. Sugar: Ribose.

6. Conceptual Insights

  • Glucose vs. Fructose: Same molecular formula (C6H12O6) but different functional groups (Aldose vs. Ketose).
  • Cellulose: Indigestible by humans because we lack the enzyme to break β-glycosidic linkages.

7. Common Mistakes

  • Anomers vs Epimers: Anomers differ only at C1 in cyclic form (e.g., α/β-Glucose). Epimers differ at any other chiral carbon.
  • DNA/RNA Bases: Uracil (U) is unique to RNA, Thymine (T) is unique to DNA.
  • Denaturation: It does not break peptide bonds (primary structure). It only unfolds the higher-order structures.

8. IAT Exam Focus Points

Key Exam Focus:

  • Hydrolysis Products:
    • Sucrose → Glc + Fru
    • Lactose → Glc + Gal
    • Maltose → Glc + Glc
  • Vitamin Solubility: Memorize Fat-soluble (ADEK) vs Water-soluble (BC).
  • Reducing Sugars: Recognize that Sucrose is non-reducing because both hemiacetal groups are involved in the glycosidic bond.

9. Practice Mock Test

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End of Chapter

Biomolecules

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