Lipids

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  • Lipids
    • Contain:
      • Hydrogen
      • Carbon
      • Oxygen
    • Consist of two different molecules: Glycerol and Fatty Acids
      • Formed by one molecule of glycerol and 3 molecules of fatty acids
        • They are therefore known as triglycerides
    • Fatty Acid structure
      • A carboxyl group (COOH)
      • A variable length hydrocarbon chain (CH2)n
        • There are always an even number of hydrogen atoms (between 2 and 14)
      • A methyl group (CH3)
    • Fatty acids can be:
      • Saturated (Fats mainly found in animals)
        • Only single bonds between carbon atoms in the hydrocarbon chain. Every bond has a hydrogen attached, so the lipid is 'saturated' with hydrogen
          • They have a high melting point and are solid at room temperature
            • A high intake of saturated fats is a contributory factor in heart disease
      • Unsaturated (Fats mainly found in plants)
        • Have more than one double bond in their hydrocarbon chain
          • This gives the molecules a kink and they tend not to pack together giving unsaturated fats a more open and oily nature
            • They have a low melting point so are liquid at room temperature e.g. plant oils
    • Formation of a triglyceride
      • Three fatty acids bond with a glycerol molecule to form a triglyceride
        • There are three condensation reactions releasing three water molecules
          • Three ester bonds are formed
      • Triglycerides are non polar so they do not attract water, therefore they are hydrophobic molecules
    • Function of Lipids
      • To act as an energy store in cells. A lipid stores twice as much energy as the same mass of carbohydrates, making it a very efficient store
        • Lipids are used in seeds to store energy
      • Although lipids have a higher energy yield/gram than carbohydrates, they cannot be broken down as quickly for use in respiration, so are used as long term energy stores in animals
      • Provide insulation (thermal) against heat loss
      • To protect vital organs in animals, e.g. heart and kidneys
      • Bouyancy in aquatic animals
      • As a source of metabolic water for organisms that live in low water environments e.g. Camels
      • Provide a waterproofing layer
    • Emulsion test for lipids/ triglycerides
      • 1. Mix the lipid with ethanol
        • 2. Pour/decant the mixture into water
          • 3. A white emulsion shows that lipid is present
    • Lipids do not dissolve in water but do dissolve in some organic solvents e.g. ethanol and acetone
    • Phospholipids
      • One fatty acid is replaced by a phosphate group (PO4 3-)
        • The phosphate group is ionised which makes is polar, so it attracts water molecules.

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