Lecture Notes: Carbon-Based Molecules and Macromolecules

Overview of Carbon Chemistry

• Carbon is fundamental in biology due to its ability to form diverse structures.
• It has 6 protons, 6 electrons, 4 valence electrons.
• Capable of forming 4 covalent bonds, leading to stable and complex molecules.
• Can bond with other carbon atoms or elements like H, O, N, P.

Types of Bonds

• Single Covalent Bonds: E.g., Methane (CH₄).
• Double Covalent Bonds: E.g., Carbon Dioxide (CO₂).
• Carbon forms chains (e.g., fatty acids) or rings (e.g., nitrogenous bases).

Macromolecules

• Composed of large number of atoms, known as polymers.
• Built from monomers via condensation reactions.
  • Types: Polysaccharides, Polypeptides, Lipids, Nucleic Acids.
  • Condensation: Two molecules bond, releasing water (H₂O).
  • Energy supplied by ATP.

Hydrolysis

• Opposite of condensation, breaks polymers into monomers using water.
• Important for digestion and metabolism.

Carbohydrates

• Known as sugars, basic unit is monosaccharide (e.g., glucose: C₆H₁₂O₆).
• Types: Monosaccharides, Disaccharides, Polysaccharides.
  • Monosaccharides: Small, soluble; quick energy source.
  • Polysaccharides: Starch, Glycogen, Cellulose.
  • Starch & Cellulose (plants), Glycogen (animals).

Glucose Structure

• Alpha and Beta forms differ by orientation of OH group on carbon 1.
• Polysaccharides differ by type of glucose and structure (branched/unbranched).

Important Polysaccharides

• Starch: Composed of alpha glucose, energy storage in plants.
• Glycogen: Similar to amylopectin, more branched; energy storage in animals.
• Cellulose: Beta glucose, structural component in plant cell walls.

Lipids

• Composed of C, H, O; hydrophobic.
• Types include fats, oils, waxes, steroids.

Fatty Acids

• Begins with carboxyl group; saturated (single bonds) vs. unsaturated (double bonds).
• Triglycerides: Three fatty acids + glycerol.
• Phospholipids: Two fatty acids + phosphate group.

Fatty Acids Structures

• Saturated (straight chains), Unsaturated (bent chains).
• Cis (same side H atoms), Trans (opposite side H atoms).

Functions and Types of Lipids

• Triglycerides: Energy storage, insulation, shock absorption.
• Phospholipids: Amphipathic; form cell membrane bilayers.
• Steroids: Four-ring structure, hydrophobic; e.g., cholesterol, hormones.

Key Concepts for IB Exam

• Understand the structure and function of macromolecules.
• Memorize glucose properties, polysaccharide types, and lipid structures.
• Recognize structural differences and their biological significance.