Medicine & USMLE

Fatty Acids

  1. Fatty Acids
  2. Triacylglycerols
  3. Phospholipids
  4. Sphingolipids
  5. Terpenes
  6. Steroids
  7. Waxes


Fatty acids are a group of lipids consisting of a carboxylic acid head connected to a long, hydrocarbon chain. Fatty acid tails can either be saturated or unsaturated. Saturated tails only consist of single carbon to carbon bonds, while unsaturated fatty acids have at least one double bond. 

Overall, fatty acids serve as building blocks for more complex lipids in the body. They are also a consumable source of energy for cells. Because of their long hydrocarbon tails, fatty acids are hydrophobic, or nonpolar, molecules.

Key Points

  • Fatty Acids
    • Structure
      • Head: Carboxylic acid
      • Attached to long hydrocarbon tail
        • Tail can be saturated or unsaturated 
          • Saturated = only single carbon-carbon bonds
            • Chain-like structure allows tight packing which causes solid state at room temperature (high melting point)
          • Unsaturated = one or more double bonds
            • Double bonded carbons changes molecular shape and prevents effective stacking of chains, causing liquid state at room temperature (low melting point)
              • Double bonds can be cis (hydrogens on same side) or trans (opposite sides)
                • Cis generates a kink/bend
    • Nonpolar/hydrophobic 
    • Role
    • Building blocks for more complex lipids
    • Consumable source of energy
      • High # of carbon-hydrogen bonds in tails stores more energy per gram than any other macromolecule in the body