Lipids

• Key lipid information


  • Only contain carbon, hydrogen, and oxygen (like carbohydrates, but with lower oxygen proportion)
  • Non-polar/hydrophobic; so insoluble in water
  • Macromolecules, **NOT POLYMERS**
  • Have no repeating subunits
  • Large and diverse group of compounds (triglycerides, phospholipids, steroids/hormones, waxes)
• Triglycerides


  • Most common lipids in living organisms
  • Join together creating globules
  • Naturally occurring ones are esters formed by condensation reactions between glycerol and three fatty acids
  • Compact and insoluble
  • Stored at high concentrations as small droplets in cell cytoplasm
  • Respiratory substance (releases twice as much energy as carbs)
  • Hydrolysed and oxidised to release energy for cell metabolism, and 'metabolic water'
  • Important to some animals; camels (go no drinking for 3 weeks due to store) or insects (never drink, only get it metabolically)
• Formation of Triglycerides 


  • Glycerol + Fatty acids (e.g. stearic acid) → Ester + 3 water
  • Ester bond formed as polar parts of glycerol molecule are lost linking to fatty acids
  • Different triglycerides are produced dependant on three fatty acids (could be same or different)
  • Fatty acids will affect their chemical and physical properties
• Fats and Oils

  • If all (or most) fatty acids are unsaturated
  • Forms oil
  • Liquid at room temperature
  • Major energy store in seeds and fruits
  • If all (or most) fatty acids are saturated
  • Forms saturated fat
  • Solid at room temperature
  • Major energy store in animals (stored as adipose)
  • Adipose, useful for;
  • Thermal insulation (mammals)
  • Protection (for delicate organs)
  • Electrical insulations (myelin sheath, prevents ion leakage)
  • Buoyancy (lipids float)
  • Triglycerides are also converted to a variety of other molecules such as:
  • Phospholipids
  • Cholesterol
  • Steroid Hormones
• Glycerol (alcohol)

  • Molecular formula is C_3H_8O_3
  • Soluble (alone) due to its three -OH groups
  • Structural formula is

  A) C

  B) C

  C) C

  D) H

  E) OH

  F) OH

  G) OH

  H) H

  I) H

  J) H

  K) H

  
• Three organic/fatty acids

  • Long, non-polar hydrocarbon chains
  • Have polar carboxyl (-COOH) group at one end (gives acidic properties)
  • Different fatty acids vary in length but are larger than glycerol
  • Fatty acids can be divided into:
  • Saturated (only single bonds)
  • Unsaturated (one or more double, C=C, bonds)