Question

From the oxidation of one molecule of palmitic acid (fatty acid), the number of ATP molecules gained as net are

• A. $131$
• B. $129$
• C. $38$
• D. $142$

Answer 1

The correct option is B $129$

The oxidation of fatty acid occurs in the following step in mitochondria:

1. activation of fatty acid

2. beta-oxidation

3. Kreb's cycle

Palmitic acid is made up of 16 carbons, so going by the formula C${}_{2n}$, then 2n=16 for palmitic acid, hence, n=8. So, 8 acetyl Co-A are produced. Now, n-1 will be the number of NADH and FADH${}_2$ produced, so, n-1=7 for palmitic acid. Hence, there will be 7 FADH${}_2$ and 7 NADH.

Now, 1 NADH gives 3 ATP, so 7 NADH will give 21 ATP

1 FADH${}_2$ gives 2 ATP, so 7 FADH${}_2$ will give 14 ATP

1 Acetyl Co-A through Kreb's cycle gives 12 ATP, so 8 Acetyl Co-A will give 96 ATP.

Hence, a total of 131 ATP will be formed. But 2 ATPs have been used in the activation of the fatty acid in the first step so, 131-2=129 ATPs as net will be formed.

Hence, the correct answer is '129'