Lipids

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  • Lipids
    • Contain carbon, hydrogen and oxygen
      • Form large molecules known as macromolecules
    • Are commonly known as oils and fats
    • Non-polar molecules
      • Because the electrons in their outer shell are more evenly distributed than those in polar molecules
      • Cannot dissolve in water because of this
    • Glycerol
      • Remains the same in all lipids
      • 3 carbon atoms with 3 OH groups
    • Fatty acids
      • Carboxylic acid group (-COOH) at one end
      • Main body is a hydrogen chain thats 2-20 carbons long)
      • Can be saturated or unsaturated
      • Fatty acids that cannot be artificially made are called essential fatty acids
    • Saturation of fatty acids
      • Unsaturated fatty acids have one or more double bond between the carbon atoms in the hydrocarbon chain
        • Polyunsaturated - more than one double bond
        • Monounsaturated - only one double bond
      • Saturated fatty acids have no double bonds between the carbon atoms in the hydrocarbon chain
      • The presence of C=c bonds cause the molecule to kink
        • Molecules cannot pack closely together
        • Are liquid at room temperature
    • Triglycerides
      • Made up of one glycerol molecule and three fatty acid molecules
      • Condensation reactions form ester bonds which link the glycerol to the fatty acids
        • Process known as esterification
        • 3 water molecules are lost forming these bonds
      • Three water molecules must be supplied to break down the triglyceride
        • Reverses the condensation reaction
        • Examles of a hydrolysis reaction
      • In the alcohol group
    • Hydrogenation
      • When double bonds are artificially brocken down and hydrogen atoms are artificially added
      • Helps some oils/fats become solid at room temperature
    • Phospholipids
      • Composed of 2 fatty acids, 1 glycerol, and a phosphate group
      • The phosphate ions contain extra electrons making them negatively charged
        • So are soluble in water
      • Have a non polar tail(fatty acid chains) and a polar head(phosphate group)
        • Non polar tails are hydrophobic
        • Polar heads are hydrophilic
      • Act as surface action agents / sufactants
      • Form bi-layer membranes
    • Sterols
      • Compex alcohol molecules based on a four carbon molecule ring structurewith a hydroxyl group at one end
      • Cholesterol is a sterol
        • Hydrophillic/hydrophobic nature allows it to sit inside cell membranes
        • Influences the fluidity and strength of the membrane
    • Emulsion test
      • Used to identify lipids
      • Mix the sample with ethanol; mix this solution with water and shake; if a white emulsion forms a layer on top then lipids are present

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