1.3 Lipids

• Name two groups of lipid

  Triglycerides and 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 structure

  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-containing group

  
• Describe how the properties of phospholipids relate to their structure

  Function: form 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 ● Phosphate heads are hydrophilic

  ○ Attracted to water so point to water (aqueous environment) either side of membrane

  ● Fatty acid tails 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