Lipids

• Macromolecules which contain carbon, hydrogen and oxygen atoms. However, unlike carbohydrates lipids contain a lower proportion of oxygen
• Non-polar?and?hydrophobic?(insoluble?in water)
• There are?two groups of lipid?that you need to know:
  • Triglycerides (the main component of fats and oils)
  • Phospholipids

   

Triglycerides

• Are non-polar, hydrophobic molecules
• The monomers are?glycerol?and?fatty acids
• Glycerol is an alcohol (an organic molecule that contains a hydroxyl group bonded to a carbon atom)
• Fatty acids contain a?methyl?group at one end of a?hydrocarbon?chain known as the R group (chains of hydrogens bonded to carbon atoms, typically 4 to 24 carbons long) and at the other is a?carboxyl?group
  • The shorthand chemical formula for a fatty acid is?RCOOH

   

• Fatty acids can vary in two ways:
  • Length?of the hydrocarbon chain (R group)
  • The fatty acid chain (R group) may be?saturated?(mainly in animal fat) or?unsaturated?(mainly vegetable oils, although there are exceptions e.g. coconut and palm oil)

   

• Unsaturated fatty acids can be?mono?or??poly-unsaturated
  • If H atoms are on the same side of the double bond they are?cis-fatty acids and are metabolised by enzymes
  • If H atoms are on opposite sides of the double bond they are?trans-fatty acids and cannot form enzyme-substrate complexes, therefore, are not metabolised. They are linked with coronary heart disease

   

Examples of different types of fatty acids with the functional groups and presence of double bonds highlighted

• Triglycerides are formed by?esterification
• An?ester bond?forms when the hydroxyl (-OH) group of the glycerol bonds with the carboxyl group (-COOH) of the fatty acid
  • The formation of an ester bond is a?condensation reaction
  • For each ester bond formed a water molecule is released
  • Three fatty acids?join to?one glycerol?molecule to form a?triglyceride
  • Therefore for one triglyceride to form,?three water molecules?are released

   

Formation of a triglyceride from a glycerol molecule and three fatty acid molecules by the process of esterification.