Lipids

• Lipid characteristics: contain carbon, hydrogen and oxygen
• Lipid characteristics: the proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates
• Lipid characteristics: they are insoluble in water
• Lipid characteristics: they are soluble in organic solvents (such as alcohols and acetone).
• The main groups of lipids are triglycerides (fats and oils) and phospholipids.
• Lipids roles: Phospholipids contribute to the felxiblity of membranes and the transfer of lipid-soluble substances across them.
• Lipids roles: source of energy
• When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuble water.
• Lipids roles: waterproofing
• Lipids are insoluble in water and therefore usefil as a waterproofing. Both plants and insects have waxy, lipid cuticles that conserve water.
• Lipids roles: insulation.
• Fats are slow conductors of heat when stored beneath the body surface help to retain body heat. They also act as electrical insulators in the meylin sheath around nerve cells.
• Lipids roles: protection
• Fat is often stored around delicate organs for protection.
• Fats are a solid at room temperature.
• Oils are liquid at room temperature.
• Triglycerides have three fatty acids combined with one glycerol molecule.
• Each fatty acid of a triglyceride forms an ester bond with glycerol in a condensation reaction.
• Hydrolysis of a triglyceride therefore prodcues glycerol and three fatty acids.
• Formation of a triglyceride:

  A) glycerol

  B) 3 fatty acids

  C) triglyceride

  
• As the glycerol molecules in all triglycerides is the same, the differences in the properties of different fats sand oils come from the variations in fatty acids.
• There are over 70 different fatty acids.
• Fatty acids all have a carboxyl (-COOH) group with a hydrocarbon chain attached.
• If the hydrocarbon chain of a fatty acid has no carbon-carbon bonds then the fatty acid is described as saturated.
• A fat is saturated when all of the carbon atoms are linked to the maximium amount of hydrogen atoms.
• If there is a single double bond in the hydrocarbon tail of a fatty acid then the fat is mono-unsaturated.
• If there is more that one double bond present in the hydrocarbon tail of a fatty acid then the fat us poly-unsaturated.
• Which type of fat is this?

  A) saturated

  
• What type of fat is this?

  A) mono-unsaturated

  
• What type of fat is this?

  A) poly-unsaturated