1.5 Lipids

1.5 Lipids

1. TRIGLYCERIDES

   • Three (tri) Fatty Acids
   • Glycerol (glyceride)
   • Each fatty acid forms an ESTER bond with glycerol in a CONDENSATION REACTION
   • Glycerol molecule is same in all moleculets but there are variations in the fatty acids meaning there are different properties
     • Saturated = NO carbon-carbon double bonds
     • Mono-unsaturated = 1 double bond
     • Polyunsaturated = More than 1 Double bond
   • High ratio of energy-storing Carbon-hydrogen bonds to carbon atoms = excellent source of energy
   • Low mass to energy ratio = good storage molecules. Beneficial to animals as reduced mass to carry around
   • Large, non-polar and insoluble = doesn't effect osmosis in cells or water potential in them
   • Triglycerides release water when oxidised, meaning they're an important source of water for organisms, especially those living in dry conditions

2. PHOSPHOLIPIDS

   • Similar to triglycerides but one fatty acid replaced with a PHOSPHATE MOLECULE
   • Fatty acid molecules - Hydrophobic 'tail'
     • Phosphate Molecules - Hydrophillic 'head'
   • Polar
   • Properties
     • Polar so form a bilayer between intercellular and extra cellular
     • Phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane. These glycolipids are important in cell recognition

3. Characteristics

   • Contain: Carbon, Oxygen and Hydrogen
   • Proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates
   • Soluble in solvents such as alcohols and acetone
   • Insoluble in water

4. Roles of Lipids

   • Source of Energy
     • When oxidised, lipids provide over 2x the energy of carbohydrates
   • Waterproofing
     • Lipids are insoluble = good at waterproofing.
       • Both plants and insects have waxy, lipid cuticles that conserve water. Where as mammals produce an oily secretion from the sebaceous glands in the skin
   • Insulation
     • Fats are slow conductors of heat meaning when stored they help retain body heat. They also act as electrical insulators in the myelin sheath around nerve cells
   • Protection
     • Fat is often stored around delicate organs

5. Testing For Lipids

   • Dry and grease-free testube
     • Add sample and ethanol
       • Shake tube throughly and dissolve lipid in sample
         • Add water, shake gently
           • Cloudy white = lipid present and emulsion formed
             • As a control, repeat the procedures using after instead of the sample; the final solution should be clear