Question

How many net ATP equivalents (including GTPs) would be produced from the complete catabolism of a 16-carbon fatty acid in the presence of oxygen (products can go through Kreb's, ETC, and ATP synthase)?

I believe the answer is 129. Can you break down the step-by-step process of this?

Answer 1

The steps involved in the fatty acid beta oxidation:
1. The activation of the fatty acid
2. Beta-Oxidation
3. Krebs Cycle.

1. The activation of the fatty acid/Charging of fatty acid:
The fatty acid molecule converts in to Fatty acyl Co.A in the presence of ATP and Co.A. The ATP undergoes two hydrolysis and forms AMP, 2Pi molecules. Due to two hydrolysis of ATP, it is considered to be 2 ATPs.

Fatty acid + CoA + ATP ------> Fatty acyl CoA + AMP + 2(P)

2. Beta oxidation:
Here the oxidation occurs at beta or second carbon, hence it is reffered as beta oxidation. During beta oxidation only two molecules of the fatty acid forms one molecule of 2c acteyl co.A., so the number of cycles form one charged fatty acid = no. of carbons in fattyacid/ 2 -1.

As the last one has two carbon molecules, it won't invovle in the further cycle.
so,

here the number of cycles from 16c fatty acid = 16/2-1 = 8-1 =7.

During each cycle of beta oxiation one NADH and one FADH2 molecules will be synthesized, the total number of NADH and FADH2 molecules from 10C fatty acid = 4 NADH and 4 FADH2.

3. Krebs cycle:
IF one acetyl co.A is involved in the kerbs cycle, it results 12 ATP molecules (3 NADH= 9 ATP, 1 FADH2 = 2ATP and 1 ATP = 12 ATP).

The total ATP molecules from 16C fatty acid =
during beta oxiation =
7NADH = 21 ATP
7FADH2 = 14 ATP

From kerbs cycle
8 Acetly Co.A = 8 x 12 = 96 ATP.

The NET ATPs = 21 + 14 + 96 - 2 = 129 ATPs.