Lipids

• Name 2 groups of lipids

  • Triglycerides
  • phospholipids
• Describe the structure of a fatty acid (RCOOH)

  • Variable R-group - hydrocarbon chain (saturated or unsaturated)
  • -COOH = carboxyl group
• Describe the difference between saturated and unsaturated fatty acids

  Saturated = no C=C double bonds in hydrocarbon chain; all carbons fully saturated with hydrogen

  Unsaturated = one or more C=C double bond in hydrocarbon chain (creating bend/kink)
• Describe how triglycerides form

  • 1 glycerol molecule and 3 fatty acids
  • Condensation reaction
  • Removing 3 water molecules
  • Forming 3 ester bonds
• Explain how the properties of triglycerides are related to their function

  Function = energy storage

  • High ratio of C-H bonds to carbon atoms in hydrocarbon chain

  So used in respiration to release more energy than same mass of carbohydrates

  • Hydrophobic/non-polar fatty acids so insoluble in water (clump together as droplets) - So no effect on water potential of cell (or can be used for waterproofing)
• Describe the difference between the structure of triglycerides and phospholipids

  One of the fatty acids of a triglyceride is substituted by a phosphate group
• What is the function of a phospholipid?

  Forms a bilayer in cell membrane, allowing diffusion of lipid-soluble (non-polar) or very small substances and restricting movement of water-soluble (polar) or larger substances
• How do the properties of phospholipids relate to their structure?

  
  

  1)Phosphate heads are hydrophilic

  • Attracted to water so point to water either side of membrane

  2)Fatty acid tales are hydrophobic

  • Repelled by water so point away from water to interior of membrane
• Describe the test for lipids

  1. Add ethanol, shake (to dissolve lipids), then add water
  2. Positive = milky white emulsion