Lipids
  • Lipids enhance the flavour of food, making it feel smoother and creamier and can supply over twice the energy of carbohydrates
  • This can be and advantage if large amounts of energy need to be consumed in a small mass of food - it also means a large amount of energy can be stored in a small mass e.g. seeds
  • Lipids are organic molecules found in every type of cell; they're insoluble in waters but soluble in organic solvents such as ethanol
  • The most common lipids that we eat are triglycerides, used as energy stores in plants and animals
  • Triglycerides are made up of three fatty acids and one glycerol molecule linked by condensation reactions
  • The bond that forms between each fatty acid and the glycerol is known as an ester bond - three are formed in a triglyceride
Saturated fats:
  • If the fatty acid chains in a lipid contain the maximum number of hydrogen atoms, they are said to be saturated.
  • In a saturated fatty acid the hydrocarbon chain is long and straight
  • There are no carbon-carbon double bonds in the saturated fatty acid chain and no more hydrogens can be added to it
  • Animal fats from meat and dairy products are major sources of saturated fats
  • Straight, saturated hydrocarbon chains can pack together closely - the strong intermolecular bonds between triglycerides made up of saturated fatty acids result in fats that are solid at room temperature
Unsaturated fats:
  • Monounsaturated fats have one double bond between two of the carbon atoms in each fatty acid chain
  • Polyunsaturated fats have a large number of double bonds
  • A double bond causes a kink in the hydrocarbon chain; these kinks prevent the unsaturated hydrocarbon packing closely together
  • The weaker the intermolecular bonds between unsaturated triglycerides result in oils that are liquid at room temperature
Other types of lipid:
  • Cholesterol is a short lipid molecule and a vital component of cell membranes with roles in their organisation and functioning
  • The steroid sex hormones and some growth hormones are produced from cholesterol
  • Bile salts, involved in lipid digestion and assimilation are formed from cholesterol
  • Therefore, cholesterol is essential for good health
  • Cholesterol is made in the liver from saturated fats and also obtained in our diet, found associated with saturated fats in foods like eggs, meat and dairy
  • However, too high a blood cholesterol level can become unhealthy
  • Phospholipids are similar to triglycerides but one of the fatty acids is replaced by a negatively charged phosphate group
  • As well as supplying energy in diet, fats also provide a source of essential fatty acids, that is, fatty acids that the body needs but can't synthesize
  • In addition, fat soluble vitamins can only enter our diet dissolved in fats - therefore, fats must be present in a balanced diet to avoid deficiency symptoms

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