Organic compounds - Lipids

Properties

• Lipids are hydrophobic.
• Mostly hydrocarbons with nonpolar bonds.
• Three families: fats, phospholipid, steroids.

Fats (Glycerides)

• Large molecules composed of glycerol and 3 fatty acids.
• Glycerol : C₃H₈O₃ alcohol
• Fatty acids
  • carboxyl head -COOH
  • long non-polar hydrocarbon tail : insoluble in H₂O.
  • water H-bonds to each other but not fats.
  • if no double bonds then a straight saturated fat (lots of H).
  • straight tails pack well : solid fat.
  • if there are double bonds then the tail is bent (unsaturated).
  • bent tails don't pack well : liquid fat.
  • Bonus: bond a metal hydroxide with a fatty acid : soap!
    • nonpolar tails mix with nonpolar grease.
    • polar heads mix with water...
    • shake : little clumps of grease surrounded by soap molecules.
    • Li soaps are used as lubricants.
    • Na soaps are solid
    • K soaps are liquid.

Phospholipid

• Molecules composed of glycerol, 2 fatty acids and phosphate group.
• Fatty acid end hydrophobic, phosphate end hydrophilic.
• Tends to form a double layer (bilayer) - tail to tail with PO₄ heads out.
• Forms a membrane !

Waxes

• Large molecules composed of alcohol and 3 fatty acids.

Steroids

• Has no fatty acids.
• Four carbon rings with various functional groups attached.
• Examples: cholesterol, some hormones (sex).