Lipids

• Generally, lipids are either fats or oils, and fats are solid at room temperature and oils are liquid.
• Lipids are non-polar molecules, so they do not dissolve in water.
• Saturated fatty acids are straight chains that pack together tightly, making them solid at room temperatures. Unsaturated fatty acids have kinks in their chain which makes it harder for them to pack together as closely, resulting in liquids at room temperature.
• Lipids are large complex molecules known as macromolecules, which are not built from repeating monomers.
• Triglycerides


  One glycerol molecules with three fatty acids.
• Fatty acids are carboxylic acids with a long hydrocarbon tail and a carboxyl group.
• Esterification

  A condensation reaction caused by the interactions of hydroxyl groups. The form an ester bond and a water molecule.
• Ester bond


  An oxygen bonded to a carbon that already has a double bond to another oxygen.
• When triglycerides are broken down, three water molecules need to be supplied to reverse the reaction that formed the triglyceride.
• Saturated 


  When a carbon chain has no double bonds.
• Unsaturated


  When a carbon chain as one or more double bonds.
• The presence of double bonds in a carbon chain cause the molecule to kink or bend and therefore cannot pack closely together. This makes the liquid at room temperature rather than solid, and they are therefore oils, not fats.
• Phospholipids


  Glycerol, two fatty acids and an inorganic phosphate group.
• Fatty acids are non-polar, and so are hydrophobic. Phosphate heads are hydrophilic.
• Hydrophilic


  Attracts water
• Hydrophobic


  Repels water.
• Lipids contain carbon, hydrogen, and oxygen.
• Phospholipids can form a two layered bilayer, with the hydrophilic head facing outwards.
• Sterols are lipids that are complex alcohol molecules.
• Cholesterol is a sterol that is primarily manufactured in the liver and intestines. They position themselves between the phospholipids in a cell membrane to regulate fluidity by keeping the membrane fluid at low temperatures and stopping it become too fluid at high temperatures.
• Roles of lipids:

  1. Membrane formation and the creation of hydrophobic barriers
  2. hormone production
  3. electrical insulation necessary for impulse transmission.
  4. waterproofing, e.g., bird feathers, plant leaves.
  5. Thermal insulation
  6. Cushioning of vital organs
  7. Buoyancy for aquatic animals
• Lipid emulsion test

  Add ethanol and water and shake. White emulsion is formed from a positive result.