1A.4 Lipids

• are lipids polymers?

  no, they are not the same unit repeating.
• what are the two types of lipids?

  triglycerides and phospholipids.
• what are triglycerides?

  one molecule of glycerol with 3 fatty acids.
• what are triglycerides used for?

  energy storage due to long hydrocarbon tails that hold lots of energy and their insolubility.
• what varies between fatty acids?

  the R group (tail).
• what are the two types of fatty acids?

  saturated and unsaturated.
• what is the difference between saturated and unsaturated fatty acids?

  • saturated fatty acids have no double bonds.• unsaturated fatty acids have some double bonds between C atoms which causes kinks.
• how are triglycerides formed?

  condensation reactions.
• what bond form between triglycerides?

  ester bond.
• what are phospholipids?


  one molecule of glycerol with one fatty acid and a phosphate group.
• what are phospholipids used for?

  make up the bilayer of the cell membrane as the head (phosphate group) is hydrophilic and the tail (fatty acid) is hydrophobic, so they form a double layer with the heads facing outwards. this stops water soluble substances from passing through.
• what is the test for lipids?

  ethanol emulsion test.
• how do you carry out a test for lipids?

  • add some ethanol to the sample.• shake for a minute.• pour into a test tube of water.• positive result = milk cloudy emulsion.
• why does a cloudy emulsion form when a sample contains lipids?

  the lipids are being finely dispersed in the water so the light is refracted.
• Why are unsaturated lipids liquid at room temp?

  the double bond means that the molecule bends and as a result parallel molecules cannot pack as closely together meaning their VDWs are weaker and the melting point is lower so liquid at room temp
• What is the COOH group called?

  Carboxyl
• how are ester bonds formed in phospholipids

  condensation reaction between one glycerol and one fatty acid producing one molecule of water
• Compare the structure of phospholipids and triglycerides

  Both are formed from condensation reactions to form an ester bond between glycerol and fatty acid chains

  the fatty acids in both of them can be saturated or unsaturated (double bonds causing kinks)

  However, phospholipids contain a phosphate group

  bound to the glycerol and triglycerides do not, and triglycerides contain three fatty acid chains whereas phospholipids contain two