Notes

• characteristics of lipids

  • contain carbon, hydrogen, + oxygen
  • insoluble in water
  • soluble in organic solvents (alcohols + acetone)
• source of energy

  provide more than 2x as much energy as the same mass of carbohydrates, and release water when oxidised
• waterproofing

  insoluble in water; plants + animals have a waxy cuticle made of lipids which conserve water
• insulation

  fats are slow conductors of heat and help to retain body heat; also act as electrical insulators in the myelin sheath around nerve cells
• protection

  fats are stored around delicate organs like the kidneys
• glycerol + 3 fatty acids —> triglyceride + 3 water
• def. triglyceride

  a group of lipids formed by the condensation of one molecule of glycerol + 3 molecules of fatty acid, joined by 3 ester bonds
• def. saturated

  an R-group of a fatty acid that has no double bonds between carbon atoms
• def. mono-unsaturated

  an R-group of a lipid that has one double bond between carbon atoms
• def. polyunsaturated

  an R-group of a lipid that has more than one double bond between carbon atoms
• double bonds in the R-group cause the molecule to bend, so they can't pack closely together and are liquid (oils) at room temperature
• phosphate + glycerol + 2 fatty acids —> phospholipid
• phospholipids are polar molecules - hydrophilic phosphate + hydrophobic fatty acid chains
• triglycerides have a high ratio of energy storing C-H bonds to C atoms 


  makes them a good source of energy
• triglycerides have a low mass to energy ratio


  makes them good storage molecules as much energy can be stored in a small volume
• triglycerides are large non-polar molecules and are insoluble in water 


  they don't affect the water potential of a cell or osmosis
• triglycerides have a high ratio of H to O atoms + release water when oxidised 


  makes them an important source of water
• phospholipids are polar molecules 


  they form a bilayer in aqueous environments within a cell-surface membrane
• the hydrophilic heads of phospholipids help to hold at the the surface of the cell-surface membrane
• phospholipid structure allows them to form glycolipids by combining with carbohydrates in the cell-surface membrane 


  glycolipids are important in cell recognition
• testing for lipids (emulsion test)

  • add 2cm^3 of the sample + 5cm^3 of ethanol to test tube + shake thoroughly to dissolve any lipid
  • add 5cm^3 of water + mix gently
  • the presence of a lipid leads to a milky-white emulsion