Lipids

• Triglycerides

  -have one molecule of glycerol with three fatty acids attached to it

  -fatty acids have hydrophobic tails (repel water molecules and make lipids insoluble in water)

  
• Saturated Fatty Acids

  Saturated - don't have any double bonds between their carbon atoms (therefore is 'saturated' with hydrogen)

  
• Unsaturated fatty acids

  Unsaturated - do have double bonds between carbon atoms, which causes the chain to kink (bend)

  
• Triglyceride Formation

  -Formed by condensation reaction between fatty acid and glycerol molecule.

  -An ester bond forms between the two molecules, releasing a molecule of water

  (this process happens twice)

  
• Phospholipids


  -found in cell membranes

  -Similar structure to triglycerides expect one of the fatty acid molecules is replaced by a phosphate group

  -The phosphate group is hydrophilic (attracts water)

  -The fatty acid tails are hydrophobic (repel water)

  
• Properties of Triglycerides

  -used as energy storage molecules

  -long hydrocarbon tails of the fatty acids contain lots of chemical energy - so a lot of energy is released when they are broken down.

  -Insoluble in water so don't affect water potential of the cell and cause water to enter the cells by osmosis

  -bundle together as insoluble droplets in cells because the fatty acid tails are hydrophobic (water-repelling) so they face inwards, shielding themselves from water with their glycerol heads.

  
• Properties of Phospholipids

  -make up the bilayer of cell membranes so control what enters and leaves a cell

  -phospholipid heads are hydrophilic and their tails are hydrophobic, so they form a double layer with their heads facing out towards the water on either side

  -the centre of the bilayer is hydrophobic so water-soluble substances can't easily pass through it

  
• Emulsion Test for Lipids

  • shake the test substance with ethanol for about a minute then pour the solution into water
  • Positive test will appear as a milky emulsion
  • (the more lipid, the more noticeable the milky colour is)