Lipids

• Lipids


  • Fuel - most common energy-storing molecules, provide twice the energy of carbs
  • Major component of cell membranes
  • Hydrophobic, nonpolar molecules
  • Fewer polar-OH groups, and more nonpolar CH bonds
• Animals have excess carbs

  Convert to fats and store fat molecules in adipose tissue for energy storage
• 4 families of lipids

  • Triglycerides
  • Phospholipids
  • Steroids/Sterols
  • Waxes
• Triglycerides

  • Built from glycerol and 3 fatty acids
  • Saturated fats have only single bonds between carbon atoms, making them solid at room temperature
  • Unsaturated/polyunsaturated fats have double bonds between carbon atoms, making them liquid at room temperature
• Triglyceride formation

  1. Glycerol reacts with fatty acids in a condensation reaction

  2. Hydroxyl and carboxyl groups form an ester linkage
• Glycerol


  • 3-C alcohol with each C bearing a hydroxyl group (OH)
  • Forms the backbone to which 3 fatty acids are attached
• Fatty acids


  • Long hydrocarbon chains ending in a carboxyl (-COOH) group
  • Can be saturated or unsaturated/polyunsaturated
• Phospholipids

  • Made of: glycerol (backbone), 2 fatty acids, & a highly polar phosphate group
  • Have a hydrophobic "tail" (fatty acid end) and a hydrophilic "head" (phosphate group)
  • Well suited to form cell membranes
• Steroids/Sterols


  • Hydrophobic molecules
  • Contain 4 fused hydrocarbon rings and several functional groups
  • Cholesterol is a component of membranes, found in blood, and a precursor of other steroids like sex hormones and vitamin D
• Waxes

  • Long-chain fatty acids linked to alcohols or carbon rings
  • Hydrophobic - so good for water-proof coatings on plants (Cutin) and animal parts (birds' waxy wings & beeswax)