Lipids

• Lipids are macromolecules which contain carbon, hydrogen and oxygen atoms, but unlike carbohydrates, lipids contain a lower proportion of oxygen
• Two groups of lipid that you need to know

  • Triglycerides
  • Phospholipids

  
• Triglycerides


  Non-polar, hydrophobic molecules made up of glycerol and fatty acids

  
• Fatty acids


  • Contain a methyl group at one end of a hydrocarbon chain and a carboxyl group at the other end
  • Can be saturated or unsaturated

  
• Formation of triglycerides


  Esterification - an ester bond forms when a hydroxyl group on glycerol bonds with the carboxyl group of a fatty acid, releasing water

  
• Saturated fatty acids


  Fatty acids with only single bonds between carbon atoms

  
• Unsaturated fatty acids


  Fatty acids with at least one carbon-carbon double bond

  
• Triglycerides


  • Store energy, provide insulation, increase buoyancy, and protect organs
• Phospholipids


  Lipids with a phosphate group attached to the glycerol, making them amphipathic (having both hydrophobic and hydrophilic parts)

  
• Phospholipids


  • Form the major component of cell membranes, creating a barrier to water-soluble molecules
  • Composition affects membrane fluidity
• The emulsion test can be used to qualitatively determine the presence of lipids in a sample
• Saturated fatty acids have only single bonds between carbon atoms, while unsaturated fatty acids have at least one carbon-carbon double bond

  
• Triglycerides are suitable for energy storage because their long hydrocarbon tails contain large amounts of chemical energy

  
• Phospholipids form a bilayer in cell membranes, with the hydrophobic fatty acid tails facing inwards and the hydrophilic phosphate groups facing outwards