Question

Why does oxidation of fatty acid give more energy?

Answer 1

Triglycerides must first be broken down into one glycerol molecule and three fatty acid chains. The glycerol can then be converted to dihydroxyacetone to be used later in glycolysis (net gain of ~2ATP from glycolysis).

The fatty acids are then activated through the addition of a ‘Coenzyme A’

The fatty acid can now undergo beta-oxidation. Long fatty acids, such as palmitate (16C) will yield more energy.

The first step is the oxidation of the alpha and beta carbons to form one double bond
This produces one molecule of FADH2
It also produces a trans-Δ2-enoyl CoA
This is hydrolysed to add an oxygen and hydrogen to the beta carbon and another hydrogen to the alpha carbon to produce L-3-hydroxyacyl CoA
Next, the L-3-hydroxyacyl CoA is oxidised to form 3-ketoacyl CoA
This produces NADH
Thiolysis now occurs which involves the addition of a CoASH group that breaks the beta carbon from the alpha carbon
This leaves Acetyl CoA and an Acyl Coa shortened by 2 carbons
The shortened Acyl CoA will repeat the beta-oxidation until no carbons are left
For palmitate, the process is completed seven times for the 16 carbons. Each time, producing one NADH, one FADH2 and one acetyl CoA. The acetyl CoA will then produce one FADH2, three NADHs and one GTP-to-be-ATP (this will occur eight times).

Therefore:

7 NADH = 17.5 ATP
7FADH2 = 10.5ATP
Minus two for the activation of the fatty acid

+

24 NADH from Krebs = 60ATP
8FADH2 from Krebs = 12 ATP
8 GTP from Krebs = 8 ATP

The total ATP yield for the beta oxidation of palmitate is 106 ATP

Compared to the average yield of 30–32 ATP from one glucose molecule in glycolysis, the Krebs cycle and oxidative phosphorylation.

This is a very simplified version, comment if you require more in depth information.

Hope this helps! :)