AQA A Level Biology Lipids

Triglycerides and phospholipids are 2 groups of lipids

\ Triglycerides -

Triglycerides are formed by the condensation of 1 molecule of glycerol and 3 fatty acids

\  A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond

\ Properties related to structure

\ Triglycerides: energy storage molecules

•High ratio of C-H bonds to C atoms in hydrocarbon tail so release more energy than the same mass of carbohydrates

• Insoluble in water (clump together as droplets) so no effect on water potential of cell Phospholipids Properties related to structure 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 Saturated & unsaturated fatty acids

\  Emulsion test for lipids

  1. Add ethanol and shake (dissolves lipids)
  2. Then add water
  3. Positive: milky/white emulsion

\ Triglycerides are formed by the condensation of 1 molecule of glycerol and 3 fatty acids