Lipid Metabolism – Beta Oxidation of Fatty Acid

Lipid Metabolism – Beta Oxidation of Fatty Acid

Lipid Metabolism is Summarized Below:
 
Lipids = Glycerol + Fatty Acid
                  ↓↑       ↓↑

              Glucose         C2 unit        ↔         Acetoacetate
                                      ↓↑
                                 CO2 + H2O

Beta Oxidation of Fatty Acid:

The degradation of fatty acid proceeds step wise by series of reactions which remove 2 carbon atoms at a time from the carboxyl end of the carbon chain. This catabolic scheme or mechanism is known as Beta oxidation which was proposed by Knoop in 1905.

This process takes place in 5 steps under control of different enzymes.

Steps in Beta-oxidation of Fatty Acids:

1) Activation of fatty acids
2) Formation of unsaturated acyl-CoA
3) Formation of Beta hydroxy Acyl CoA
4) Formation of Beta-keto acyl CoA   
5) Thiolytlc cleavage of Acyl CoA

Acyls CoA enter in citric acid cycle and oxidized to CO2 and H2O and produce ATP molecules.

Energy from Oxidation of Fatty Acid:

Ex. palmitic acid (16 carbon) yield 8 molecules of acetate and run through the Beta oxidation cycle 7 times. Oxidation of a carbon (one cycle) yield 5 ATP (7 x 5 = 35 ATP) and 8 molecules of acetate where oxidized in TCA will produce (8 x 12 = 96). Total ATP = 35 + 96 = 131. Loss of 2 energy rich phosphate at activation step hence 131-2 = 129 ATP net gained.