Lecture on Lipids

Introduction to Lipids

• Lipids are carbon-containing compounds.
• Characterized by insolubility in water (hydrophobic due to nonpolar C-H and C-C bonds).
• Dissolve in nonpolar organic solvents (e.g., benzene).

Properties of Lipids

• Hydrophobic: Insoluble in water due to nonpolar bonds.
• Energy Storage: Contain twice as much energy as polysaccharides.
• Structure:
  • Composed mainly of carbon and hydrogen atoms.
  • Not built from monomers like other macromolecules (carbohydrates, proteins, nucleic acids).
  • Vary widely in structure and function.

Types of Lipids

1. Fats

   • Nonpolar molecules, also known as triacylglycerols or triglycerides.
   • Composed of three fatty acids linked to glycerol.
   • Primary role is energy storage. Store twice as much energy as carbohydrates.
   • Formed via dehydration reactions creating ester linkages (important for Bio 181).
   • Not considered polymers, as fatty acids are not linked into chains.

2. Phospholipids

   • Major component of cell membranes.
   • Consist of glycerol linked to a phosphate group and two hydrocarbon chains.
   • Amphipathic: Possess both hydrophilic (polar head) and hydrophobic (nonpolar tail) regions.
   • Formed from glycerol, phosphate group, and additional small organic molecules.
   • Form bilayers in cell membranes, with hydrophilic heads outward and hydrophobic tails inward.

3. Steroids

   • Synthesized from cholesterol.
   • Contain a four-ring carbon structure.
   • Examples: Cholesterol, which is important in cell membrane structure and fluidity.
   • Types include fat steroids (insoluble in water) and protein steroids (e.g., insulin).

Structure and Function Considerations

• Saturated vs. Unsaturated Fats

  • Saturated: Only single bonds, dense, solid at room temp (e.g., butter).
  • Unsaturated: One or more double bonds, less dense, liquid at room temp (e.g., oils).
  • Saturation affects physical state and nutritional value (polyunsaturated fats may protect the heart).

• Hydrogenation and Trans Fats

  • Hydrogenation adds hydrogen, converting unsaturated to saturated fats.
  • Produces trans fats, which are linked to increased heart disease risk.

Applications

• Biological Importance
  • Energy storage, membrane structure, signaling.
  • Phospholipids crucial for forming cell membranes.
  • Steroids serve as important signaling molecules.

The lecture wraps up with an emphasis on the importance of cholesterol in producing necessary steroids and its role in cell membrane integrity.