Lecture Notes: Lipids

Overview of Lipids

• Lipids are non-polar hydrocarbons, hydrophobic (water-fearing).
• Function in different environments (e.g., aquatic animals' fur).
• Functions of Lipids:
  • Long-term energy storage.
  • Physical and temperature insulation.
  • Component in hormones and cell membranes.

Types of Lipids

• Fats

  • Comprised of glycerol and three fatty acids (triacylglycerol/triglyceride).
  • Formation through ester linkage, dehydration synthesis.
  • Fatty Acids
    • Long hydrocarbon chains with carboxyl group.
    • Chain length: 4 to 36 carbons (commonly 12 to 18).
    • Saturated Fatty Acids
      • Single bonds in hydrocarbon chain.
      • Examples: Stearic acid, solid at room temp.
      • Associated with cardiovascular disease.
    • Unsaturated Fatty Acids
      • One or more double bonds (monounsaturated or polyunsaturated).
      • Kinked structure due to double bonds, liquid at room temp (e.g., olive oil).
    • CIS and Trans Fats
      • CIS: Hydrogens on the same side, kinked, liquid at room temp.
      • Trans: Hydrogens on opposite sides, more solid, unhealthy.
      • Trans Fats: Created by hydrogenating oils.

• Essential Fatty Acids

  • Required in the diet, not synthesized by the body.
  • Omega-3 and Omega-6
    • Sources: Fish (Omega-3), nuts (Omega-6).

• Waxes

  • Long fatty acid chains bonded to long-chain alcohols via ester linkage.
  • Waterproofing agent (e.g., feathers, plant leaves).

• Phospholipids

  • Components of cell membranes.
  • Structure: Two fatty acid tails (hydrophobic) + glycerol + phosphate group (hydrophilic).
  • Amphipathic molecule: Hydrophilic head, hydrophobic tails.
  • Phospholipid bilayer: Cell membrane structure, dynamic/fluid nature.

• Steroids

  • Fused ring structure: Three six-sided rings, one five-sided ring.
  • Hydrophobic and nonpolar.
  • Cholesterol: Essential for hormone production (e.g., testosterone, estrogen), vitamin D, and bile salts.
  • Steroids can pass through cell membranes easily (lipophilic).

Important Concepts

• Phospholipid Bilayer: Provides a selective barrier for cells.
• Role of Steroids in Membrane Fluidity: Maintains proper membrane consistency.
• Heart Disease: Linked more with saturated fats than with dietary cholesterol.

Next Topic

• Introduction to Proteins (next video)