Lipids

• Lipids

  Triglycerides and phospholipids are 2 groups of lipids
• Triglyceride formation

  1. Condensation of 1 molecule of glycerol and 3 fatty acids

  2. Condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond
• Triglycerides

  • Energy storage molecules
  • High ratio of C-H bonds to C atoms in hydrocarbon tail
  • Release more energy than the same mass of carbohydrates
  • Insoluble in water (clump together as droplets)
  • No effect on water potential of cell
• Phospholipids

  • Form bilayer in cell membrane, allowing diffusion of non-polar/small molecules
  • Phosphate heads are polar/hydrophilic so are attracted to water → orient to aqueous environment either side of membrane
  • Fatty acid tails are non-polar/hydrophobic so are repelled by water orient to interior of membrane → repels polar/charged molecules
• Fatty acid types


  • Saturated: no C=C double bonds in hydrocarbon chain; all carbons fully saturated with hydrogen
  • Unsaturated: one or more C=C double bonds in hydrocarbon chain
• Emulsion test for lipids


  1. Add ethanol and shake (dissolves lipids)

  2. Then add water

  3. Positive: milky/cloudy white emulsion