12 - Lipids and Membranes

Lecture Information

Title: Lipids and MembranesInstructor: David N. LangelaanLocation: Room 8F, Tupper Medical BuildingContact: dlangela@dal.caContent Questions: BIOC2300@dal.ca

Session Objectives

  • Describe major lipid classes: Fatty Acids, TAGs, Phospholipids, Steroids, Glycolipids.

  • Apply fatty acid nomenclature.

  • Explain the fluid mosaic model and lipid membrane properties.

Lipid Characteristics

  • General Properties: Hydrophobic or amphipathic; not free in solution. Storage and transport challenges due to aggregation.

  • Classification:

    • By structure:

      • Fatty Acids (FA): Aliphatic carboxylic acids.

      • Triacylglycerols (TAGs): Esters of 3 FA and glycerol.

      • Phospholipids (PLs): Phospho-head with diacylglycerol/ceramide.

      • Steroids: E.g., cholesterol.

      • Glycolipids: E.g., glycosphingolipids.

    • By function: Membrane structures, energy storage, bioactive compounds.

Fatty Acids

  • Characteristics: Amphipathic with a hydrophilic group and hydrophobic tail.

  • Types: Saturated, mono-, and poly-unsaturated.

  • Nomenclature:

    • Omega: Count from the tail (e.g., α-linolenic acid: 18:3(n-3)).

    • Delta: Count from the carboxyl group (e.g., α-linolenic acid: 18:3(9,12,15)).

  • Essential fatty acids must be obtained from the diet.

Triacylglycerols (TAGs)

  • Consist of 3 fatty acids and glycerol; major energy reserve, stored in adipose tissue.

Phospholipids (PLs)

  • Major cell membrane components; variations in headgroups affect function.

Cholesterol

  • Maintains membrane fluidity; requires transport via lipoproteins; involves health risks if imbalanced.

Biological Membranes

  • Fluid Mosaic Model: Composed of lipids (PLs, cholesterol) and proteins; allows lateral movement but not flip-flop.

  • Factors affecting fluidity: Degree of saturation, chain length, and presence of cholesterol.

Membrane Proteins

  • Types:

    • Integral: Non-polar interactions, traverses bilayer.

    • Peripheral: Interacts with the membrane surface.

Key Terms

  • Lipid, amphipathic, fatty acid, eicosanoid, triacylglycerol, phospholipid, cholesterol, fluid mosaic model, integral and peripheral proteins.