Lecture Notes: Lipids

Introduction to Lipids

• Lipids include fats and oils.
• Types of lipids:
  • Fatty acids
  • Triglycerides
  • Phospholipids
  • Steroids
  • Waxes
  • Terpenes
  • Prostaglandins
• Characteristics:
  • Nonpolar, mostly hydrophobic (do not mix well with water).
  • Composed primarily of carbon-hydrogen (CH) bonds.
  • May contain oxygen, nitrogen (in phospholipids), and phosphorus.

Functions of Lipids

• Long-term energy storage (e.g., triglycerides).
  • When fasting, after depleting carbohydrates, the body uses triglycerides.
  • Lipase enzyme breaks down triglycerides into fatty acids and glycerol.
• Structural role in cell membranes (phospholipids).
• Provide thermal insulation and protection.

Fatty Acids

• Long hydrocarbon chains with a carboxylic acid group.
• Polar (hydrophilic) head and non-polar (hydrophobic) tail.
• Types:
  • Saturated fatty acids: No double bonds, solid at room temperature (e.g., butter).
  • Unsaturated fatty acids: Have double bonds, liquid at room temperature (e.g., vegetable oils).
  • Trans fatty acids: Hydrogen atoms on opposite sides of the double bond.

Triglycerides

• Composition: 3 fatty acids + 1 glycerol molecule.
• Formed by dehydration synthesis (losing water molecules in the process).
• Function: Efficient energy storage, nonpolar.
• Can be broken down by hydrolysis (adding water).

Phospholipids

• Made of a phosphate group, glycerol, and two fatty acid chains.
• Contain carbon, hydrogen, oxygen, phosphorus, and nitrogen.
• Key component of cell membranes (phospholipid bilayer).
• Have a polar head (phosphate group) and non-polar tails (fatty acids).

Steroids

• Characterized by four fused rings.
• Examples:
  • Cholesterol: Maintains cell membrane fluidity.
  • Estradiol: Primary female sex hormone.
  • Testosterone: Primary male sex hormone.
  • Cortisol: Reduces inflammation, known as hydrocortisone when medicated.

Waxes

• Nonpolar, long alkyl chains, high melting points.
• Examples: Beeswax, plant waxes, paraffin wax.
• Used for waterproofing and protection.

Terpenes

• Basic unit: Isoprene (5 carbon atoms, diene).
• Examples include limonene (found in citrus peels) and beta-carotene (found in carrots).
• Terpenes have carbon atoms in multiples of five.

Eicosanoids

• Categories: Prostaglandins, Thromboxanes, Leukotrienes.
• Prostaglandins: Vasodilators, inhibit platelet aggregation.
• Thromboxanes: Facilitate platelet aggregation, vasoconstrictors.
• Leukotrienes: Inflammatory mediators, signal molecules.

Conclusion

• Review of different lipid types and their functions.
• Importance in biological systems and energy storage.