1.3 lipids

• name two groups of lipids

  triglycerides and phospholipids
• structure of a fatty acid

  variable R-group - hydrocarbon chain (saturated or unsaturated)

  COOH group is a carboxyl group
• differences between saturated and unsaturated fatty acids

  saturated has no c=c double bonds in hydrocarbon chain as all carbons are fully saturated with hydrogen

  unsaturated has one or more c=c double bond in hydrocarbon chain (creating bend/link)
• describe how triglycerides form

  1 glycerol molecule and 3 fatty acids

  condensation reaction

  removing 3 water molecules

  forming 3 ester bonds
• how the properties of triglycerides are related to their structure

  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)
• difference between the structure of triglycerides and phospholipids

  one of the fatty acids of a triglycerides is substituted by a phosphate-containing group
• describe how the properties of phospholipids relate to their structure

  phosphate heads are hydrophilic so are attracted to water so point to water (aqueous environment) either side of membrane

  fatty acid tails are hydrophobic so repelled by water so point away from water/to interior of membrane
• function of phospholipids

  form a bilayer in cell membrane, allowing diffusion of lipid-soluble (non-polar) or very small substance and restricting movement of water-soluble (polar) or larger substances
• function of triglycerides

  energy store
• test for lipids

  add ethanol

  shake to dissolve lipids

  add water

  positive result is a milky white emulsion