Lipids

• what 3 atom types do lipids contain ?

  1. carbon
  2. hydrogen
  3. oxygen
• What are the 2 groups of lipid?

  1. Triglycerides
  2. Phospholipids
• What are the bonds involved in the formation of a Triglyceride?

  Ester bond during esterfication
• Triglyceride formation image :

  =

  
• How can fatty acids vary?

  • Length of the hydrocarbon chain (R group)
  • The fatty acid chain (R group) may be saturated or unsaturated 
• Basic structure of a fatty acid image :

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• What's the structure of a triglyceride ?

  • 1 molecule of glycerol and 3 fatty acid attached
  • the fatty acids have long 'tails' made up of hydrocarbons
  • The tails are hydrophobic (repel water) and non-polar
  • These tails make the lipids insoluble in water
  • all fatty acids have the same basic structure but the hydrocarbon tail varies

  
• How are Triglycerides formed?

  • Condensation reaction
  • a fatty acids joins to a glycerol molecule - an ester bond is formed
  • a molecule of water is released
  • The process happens twice more to form a triglyceride

  
• What are the 2 types of fatty acid ?

  1. Saturated
  2. Unsaturated
• What is a saturated fatty acid ?

  • don't have any double bonds between their carbon atoms
  • (the fatty acid is "saturated" with hydrogen)

  
• What is an unsaturated fatty acid?

  • have at least one double bond between carbon atoms which cause the chain to kink
  • potential to combine with other bonds

  
• where are phospholipids found ?

  Cell membranes
• What is the structure of a phospholipid?

  • contains one phosphate group, one glycerol and 2 fatty acid molecules
  • Their heads (phosphate group) are hydrophilic (attracts water)
  • Their fatty acid tails are hydrophobic (repel water)

  A) hydrophobic

  B) hydrophilic

  
• How does the structure of a Phospholipid relate to its function? ( making up the bilayer of cell membranes)

  1. Their heads are hydrophilic and their tails are hydrophobic so they form a double layer with their heads facing out towards the water on either side.
  2. The center of the bilayer is hydrophobic, so water-soluble substances cant easily pass through it - the membrane acts like a barrier to those substances

  
• How does the structure of a Triglyceride relate to its function as an energy storage molecule ?

  1. The long hydrocarbon tail of the fatty acids contain lots of chemical energy - lots is released when they are broken down (lots of carbon/hydrogen bonds)
  2. They are insoluble - don't affect the water potential of the cell and cause water to enter by osmosis (which would make them swell)
  3. easily be stored because they have a low mass

  
• What is the test for lipids ?

  • Emulsion Test
  • shake the test substance with ethanol for around a minute so it dissolves and then pour the solution into water
  • Any lipid will present as a milky emulsion
  • The more lipid there is - the more noticeable the milky colour will be

  
• Non polar molecules are ..

  • hydrophobic ( don't dissolve in water)
• Solubility of Lipids ?

  1. insoluble in water
  2. soluble in organic solvents e.g. alcohol
• what's lipids role ?

  • cell membranes (phospholipid bilayer)
  • source of energy
  • Waterproofing
  • insulation (fats are slow heat conductors and electrical insulators)
  • Protection
• In a Phospholipid whats the bond in-between the phosphate group and the glycerol molecule?

  • Phosphoester bond
• Differences between Triglycerides and Phospholipids

  1. Triglycerides have 3 fatty acid chains but phospholipids have 2
  2. Phospholipids contain a phosphate - triglycerides do not
  3. functions = phospholipids - cell membranes component (phospholipid bilayer) triglycerides - energy storage
• polar molecules are....

  • hydrophilic