2 faty acids

• Free fatty acids released by lipolysis enter circulation and are transported bound to albumin.
• About 95% of the energy obtained from fat comes from the oxidation of fatty acids.
• Certain tissues, such as the brain and erythrocytes, cannot oxidize fatty acids.
• β-oxidation


  Oxidation of fatty acids on the β-carbon atom
• Stages of β-oxidation


  1. Activation of fatty acids

  2. Transport into mitochondria

  3. β-Oxidation proper
• Fatty acids are oxidized by most tissues in the body.
• Brain, erythrocytes, and adrenal medulla cannot utilize fatty acids for energy requirement.
• Activation of fatty acids

  1. Fatty acids activated to acyl CoA

  2. Requires ATP, coenzyme A, and Mg2+
• Transport of Acyl CoA into mitochondria

  1. Acyl group transferred to carnitine

  2. Transported across membrane

  3. Converted back to acyl CoA

  4. Carnitine returns to cytosol
• Carnitine acyl transferase I is inhibited by malonyl CoA.
• β-Oxidation proper


  1. Oxidation by acyl CoA dehydrogenase

  2. Hydration by enoyl CoA hydratase

  3. Second oxidation by β-hydroxyacyl CoA dehydrogenase

  4. Cleavage by β-ketoacyl CoA thiolase
• Each cycle of β-oxidation liberates a two carbon unit, acetyl CoA.
• Palmitoyl CoA undergoes 7 cycles of β-oxidation to yield 8 acetyl CoA.
• Acetyl CoA can enter the citric acid cycle and get completely oxidized to CO2 and H2O.
• The energy yield by the oxidation of palmitic acid is 129 ATP.
• The efficiency of energy conservation by fatty acid oxidation is 40%.
• β-oxidation of odd carbon chain fatty acids leaves behind a three-carbon fragment, propionyl CoA.
• Propionyl CoA is converted to succinyl CoA for the TCA cycle.
• Oxidation of unsaturated fatty acids provides less energy than that of saturated fatty acids.
• Fatty acid oxidation is accompanied by the production of metabolic water.
• Camel can store lipids in its hump, which is a good source of water and energy supply.