Triglycerides: Basics

• Lipids


  Macromolecules which contain carbon, hydrogen and oxygen atoms, but have a lower proportion of oxygen compared to carbohydrates. They are non-polar and hydrophobic, so they are insoluble in water.
• Types of lipids


  • Fats and Oils (composed mainly of triglycerides)
  • Phospholipids
  • Steroids and waxes
• Triglycerides


  Non-polar, hydrophobic molecules composed of glycerol and fatty acids

  
• Glycerol


  • 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 (chains of hydrogens bonded to carbon atoms, typically 4 to 24 carbons long) and a carboxyl group at the other end

  
• Fatty acids


  • Can vary in length of the hydrocarbon chain and 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.
• Triglyceride formation


  Esterification - An ester bond forms when the hydroxyl group of the glycerol bonds with the carboxyl group of the fatty acid, releasing a water molecule. Three water molecules are released for one triglyceride to form.

  
• Triglycerides are formed by esterification
• Triglycerides


  • Store more energy per gram than carbohydrates and proteins (37kJ compared to 17kJ), do not cause osmotic water uptake in cells so more can be stored, and their oxidation releases metabolic water
• Triglyceride storage


  • Plants store triglycerides, in the form of oils, in their seed and fruits. Mammals store triglycerides as oil droplets in adipose tissue.

  
• Triglycerides


  • Provide insulation by being part of the myelin sheath around nerve fibres and the adipose tissue layer below the skin, increase buoyancy, protect organs, and provide waterproofing