1.5 - Lipids

• What are the 2 groups of lipids ?


  Triglycerides and Phospholipids
• What are lipids insoluble in ?


  Water
• What are lipids soluble in ?


  Organic solvents like alcohols and acetone
• 1 role of lipids in cells ?


  In the cell membranes (cell-surface and organelle)
• 4 other roles of lipids ?


  Energy, Waterproofing (as they’re insoluble in water), Insulation, Protection for organs
• States of fats and oils at room temperature ?


  Fats are solids whereas oils are liquids
• What makes up a triglyceride ?


  3 fatty acids and a glycerol
• How is a triglyceride formed and what bonds are made ?


  Formed by a condensation reaction between fatty acids and a glycerol, creating an ester bond
• What‘s the structure of a fatty acid ?


  A carboxyl group with a hydrocarbon chain attached
• What can the R-group of a fatty acid be ?


  Saturated or unsaturated
• What would the fatty acid be called if it had a single double bond ?

  Mono-unsaturated
• What would a fatty acid be called if it had more than 1 double bond ?


  Polyunsaturated
• When the condensation reaction occurs, which component loses the hydroxyl group and which loses a hydrogen ?


  The fatty acid loses the hydroxyl and the glycerol loses the hydrogen
• Why are triglycerides a good energy source ?


  Have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms
• Why are triglycerides good storage molecules ?


  Have a low mass to energy ratio so much energy can be stored in a small volume
• Why does triglyceride storage not affect osmosis in cells ?


  They are large, non-polar and insoluble in water (don’t effect water potential)
• Why are triglycerides an important source of water ?


  They release water when oxidised
• What’s a phospholipid compared to a triglyceride?


  One of the fatty acid molecules is replaced by a phosphate molecule
• The 2 components of a phospholipid ?


  Phosphate head and fatty acid tail
• Key property of the phosphate head ?


  It’s hydrophilic so water is attracted to it but it doesn’t interact with fat
• Key property of the fatty acid tail ?


  It’s hydrophobic which repels water but mixes readily with fat
• Why are phospholipids described as polar ?

  Have 2 poles that behave differently
• What do phospholipids do in an aqueous solution ?


  Form a bilayer within cell-surface membranes, forming a hydrophobic barrier between the inside and outside of the cell
• What does the phospholipid structure allow them to form ?


  Glycolipids by combining with carbohydrates within the cell-surface membrane (important for cell regeneration)
• What’s the test for lipids known as ?

  The emulsion test
• Method for the emulsion test ?


  Add 5cm3 of ethanol to 2cm3 of the sample, shake to dissolve any lipids, add 5cm3 of water and shake, a milky-white emulsion indicates the presence of a lipid
• What would the control of the emulsion test be ?


  Repeat the test using water instead of the sample, final solution should be clear