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

 
Hint: The most common form of fatty acid that contains sixteen carbon atoms and no double carbon- carbon bonds is palmitic acid. A total of seven cycles of beta-oxidation must take place to fully break down the fatty acids.

Complete Step by Step Answer: 16 carbon atoms together form palmitic acid. So, by going with the formula $C_{2n}$, then 2n = 16. Thus, n = 8. Therefore, 8 Acetyl CoA is formed. Since (n - 1) is equal to the number of NADH and $FAD{H}_2$, so (n - 1) = 7 for palmitic acid. Hence, there will be 7 NADH and 7 $FAD{H}_2$.
1 NADH = 3 ATP Therefore, 7 NADH = 7*3 = 21 ATP 1 $FAD{H}_2$ = 2 ATP Therefore, 7 $FAD{H}_2$ = 7*2 = 14 ATP
1 Acetyl CoA through TCA cycle produce 12 ATP Then, 8 Acetyl CoA will give (12*8) = 96 ATP
Total ATP produced are = 21 + 14 + 96 = 131 ATP But since 2 ATP is used to activate the fatty acid in the first step Therefore, 131 - 2 = 129 ATP Thus, from the oxidation of one molecule of palmitic acid, the number of ATP molecules released is 129 ATP.

Additional Information: In the presence of CoA-SH and acyl-CoA synthetase, fatty acids are activated before oxidation, using ATP. Long chain acyl-CoA joins the carnitine- bound mitochondria. Beta oxidation of fatty acids occurs within mitochondria, in which two carbon atoms are separated from acyl-CoA at the carboxyl-terminal in the form of acetyl-CoA. The bond, hence the name beta- oxidation, is broken between the second carbon/beta carbon and the third carbon/gamma carbon. This system supplies energy from fats.
- The fatty acid oxidation rate is high during fasting but low in the fed animal. The higher concentration of unesterified (free) fatty acids in the bloodstream of the fasting animal relative to the concentration in the fed animal is one cause of this transition.
So, the answer is, “129.”

Note: - Fatty acid oxidation occurs in mitochondria at the following stage: Fatty Acid Activation Oxidation of beta TCA cycle - The mitochondrial aerobic mechanism of breaking down a fatty acid into acetyl-CoA units is fatty acid oxidation. Fatty acids travel as CoA derivatives using NAD and FAD in this pathway. - The main metabolic pathway by which energy is released from fatty acids is $\beta$- Oxidation. The intracellular concentration of 'free' (i.e., unesterified) fatty acids, which in turn is determined by their concentration in the blood, regulates the rate of fatty acid $\beta$- oxidation.