🥛Lipids 🥛

• Fats are lipids that are solid at room temperature
• Oils are lipids that are liquid at room temperature
• lipids are non-polar so they are not soluble in water
• lipids are large, complex molecules = macromolecules
• a triglyceride is made by combining one glycerol molecule with three fatty acids

  Glycerol is an alcohol

  Fatty acids are carboxylic acids
• The three hydroxyl groups of the glycerol molecule react in condensation reactions with the hydroxyl groups of the fatty acids forming ester bonds that hold the resulting triglyceride together

  Three water molecules are also produced

  This reaction is called esterification
• fatty acid chains that have no double bods between carbon atoms are saturated
• fatty acid chains that have one double bond in the carbon chain are monounsaturated
• fatty acid chains that have more than one double bond in the carbon chain are polyunsaturated
• the presence of double bonds in the carbon chains of fatty acids causes the molecule to bend/kink and so they can't pack closely together

  This makes the lipid liquid at room temperature so it is therefore an oil
• plants contain unsaturated triglycerides and they tend to be more healthy in the human diet than saturated triglycerides
• Phospholipids are modified triglycerides

  One of the fatty acid chains in the triglyceride is replaced with a phosphate group

  This results in a phospholipid with a charged, hydrophilic head and two non-polar, hydrophobic tails
• Phospholipids are surface active agents (surfactants) because they form a layer on the surface of water with the phosphate heads in the water and the fatty acid tails sticking out
• Phospholipids can form bilayers with the hydrophobic tails facing towards the centre of the sheet, protected from the water by the hydrophilic heads
• Sterols are another type of lipid found in cells

  They are complex alcohol molecules based on a four carbon ring structure with a hydroxyl group at one end

  They have dual hydrophobic and hydrophilic characteristics like phospholipids do
• Cholesterol is a sterol

  It adds stability to cell membranes and regulates their fluidity
• The non-polar nature of lipids means they are used for:

  • membrane formation and creation of hydrophobic barriers
  • hormone production
  • electrical insulation necessary for impulse transmission
  • Waterproofing (birds feathers and plant leaves)
• Triglycerides are important for long term energy storage.

  They are stored under the skin and around vital organs where they also provide:

  • thermal insulation to reduce heat loss
  • cushioning to protect vital organs
  • buoyancy for aquatic animals
• Lipids can be identifyed in the lab by the emulsion test:

  • first the sample is mixed with ethanol
  • the resulting solution is mixed with water and shaken
  • if white emulsion forms as a layer on top of the solution then lipid is present
  • If the solution remains clear no lipids are present