Lipids and Biological Membranes Notes

Cell Membrane and Lipids

• Cell: Basic unit of life; develops from fertilized egg to trillion cells, each surrounded by a cell membrane.

Membrane Lipids

• Definition: Membrane lipids are amphipathic molecules, meaning they have both hydrophobic (water-fearing) and hydrophilic (water-loving) regions.
  • Structure: Composed of a polar head and non-polar tails.
• Key Example: Phosphatidylcholine.

Membrane Structure

• Formation: Membrane lipids form a bilayer:
  • Forces Driving Formation:
  • Hydrogen bonds and electrostatic forces (polar heads with aqueous environment).
  • Hydrophobic interactions (non-polar tails).
  • Van der Waals forces contributing to close packing.
  • Characteristics:
  • Weak forces allow lateral movement (fluidity).
  • Impermeable to water, ions, and polar molecules.

Types of Membrane Lipids

• Predominant: Phosphoglycerides, which are characterized by a glycerol backbone combined with fatty acids and phosphate groups.
  • E.g., Phosphatidylcholine has a choline group as the alcohol.
• Four Major Phosphoglycerides:
  1. Phosphatidylcholine
  2. Phosphatidylserine
  3. Phosphatidylethanolamine
  4. Phosphatidylinositol

Fatty Acids

• Structure: Composed of a hydrocarbon chain and a carboxyl group.
  • Saturation and types:
  • Saturated: No double bonds (e.g., Palmitic acid).
  • Unsaturated: One or more double bonds (mono-unsaturated and polyunsaturated).
  • Cis and Trans forms affect fluidity.
• Nomenclature:
  • Carbon counting from carboxyl or last carbon (ω positions).

Membrane Fluidity

• Factors Influencing Fluidity:
  • Saturation of fatty acids: More unsaturation leads to looser packing and greater fluidity.
  • Length of fatty acid chains: Longer chains lead to less fluidity.

Omega Fatty Acids

• Importance: Both Omega-3 and Omega-6 fatty acids are essential for human health.
  • Examples:
  • Omega-6: Linoleic acid (18:2)
  • Omega-3: Alpha-linolenic acid (ALA, 18:3)
  • Other significant Omega-3s: Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA).

Glycolipids and Cell Recognition

• Definition: Membrane lipids with sugar groups vital for cell recognition.
  • Functions: Cell-cell adhesion, migration, and immune response.

Cholesterol

• Role: A type of membrane lipid that enhances membrane fluidity while also providing stability.

Membrane Proteins

• Functions: Variety of functions, including:
  • Transport (channels and pumps: Na+, K+ transporters, insulin).
  • Receptor activity.
• Types: Integral (span the membrane) and peripheral membrane proteins.

Signaling Molecules

• Example: PTGS1 (Prostaglandin-Endoperoxide Synthase 1) produces arachidonic acid-derived signaling molecules (prostaglandins) that mediate pain and inflammation.
• Effect of Aspirin: Blocks PTGS1 and reduces prostaglandin production, alleviating pain and inflammation.

Triacylglycerol (TAG)

• Definition: Not a membrane lipid; serves as a storage form of lipids.

Key Study Points

• Understand chemical properties of membrane lipids (amphipathic) and forces driving bilayer formation.
• Structure of fatty acids: hydrocarbon + carboxyl.
• Saturation: location and type of double bonds; influence on fluidity.
• Key features of membrane lipids (phosphoglyceride, glycolipid, cholesterol) and characteristics of membrane proteins.
• Impact of aspirin on pain and related biochemistry of PTGS1.