BETA-OXIDATION

Beta-oxidation is the process by which fatty acids, in the form of acyl-CoA molecules, are
broken down in mitochondria and/or peroxisomes to generate acetyl-CoA, the entry molecule for
the citric acid cycle.
The beta oxidation of fatty acids involve three stages:
1. Activation of fatty acids in the cytosol
2. Transport of activated fatty acids into mitochondria (carnitine shuttle)
3. Beta oxidation proper in the mitochondrial matrix
Fatty acids are oxidized by most of the tissues in the body. However, some tissues such as the
adrenal medulla do not use fatty acids for their energy requirements and instead use
carbohydrates.
Energy yield
The ATP yield for every oxidation cycle is 14 ATP (according to the P/O ratio), broken down as
follows:
Source ATP Total
1 FADH2 x 1.5 ATP = 1.5 ATP (some sources say 2 ATP)[citation needed]
1 NADH x 2.5 ATP = 2.5 ATP (some sources say 3 ATP)
1 acetyl CoA x 10 ATP = 10 ATP (some sources say 12 ATP)
TOTAL = 14 ATP
For an even-numbered saturated fat (C2n), n - 1 oxidations are necessary, and the final process
yields an additional acetyl CoA. In addition, two equivalents of ATP are lost during the
activation of the fatty acid. Therefore, the total ATP yield can be stated as:
(n - 1) * 14 + 10 - 2 = total ATP
For instance, the ATP yield of palmitate (C16, n = 8) is:
(8 - 1) * 14 + 10 - 2 = 106 ATP
Represented in table form:
Source ATP Total
7 FADH2 x 1.5 ATP = 10.5 ATP
7 NADH x 2.5 ATP = 17.5 ATP
8 acetyl CoA x 10 ATP = 80 ATP
Activation = -2 ATP
NET = 106 ATP
For sources that use the larger ATP production numbers described above, the total would be 129
ATP ={(8-1)*17+12-2} equivalents per palmitate.
Beta-oxidation of unsaturated fatty acids changes the ATP yield due to the req