TBR Biology Chapter 8 Passage 7 #38

[Jengreef]

The question asks how many ATPs are produced from the complete oxidation of Caprylic Acid,which is an 8-carbon saturated fatty acid.

Part of finding the answer to this is calculating how many times this molecule undergoes beta oxidation. The solution states 4 times. But after 3 rounds, we should only have two molecules of acetyl CoA remaining (6 carbon chain and 2 carbon chain after the first round; 4 and 2 after the second round; 2 and 2 in the third round, which is simply two acetyl CoA, which do not undergo beta oxidation again)

The confusing thing is the solutions acknowledge that caprylic acid is only oxidized thrice in the very next paragraph. So is the solutions wrong, or am I misunderstanding what one round of beta oxidation actually amounts to?

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[Captain Sisko]

The question asks how many ATPs are produced from the complete oxidation of Caprylic Acid,which is an 8-carbon saturated fatty acid.

Part of finding the answer to this is calculating how many times this molecule undergoes beta oxidation. The solution states 4 times. But after 3 rounds, we should only have two molecules of acetyl CoA remaining (6 carbon chain and 2 carbon chain after the first round; 4 and 2 after the second round; 2 and 2 in the third round, which is simply two acetyl CoA, which do not undergo beta oxidation again)

The confusing thing is the solutions acknowledge that caprylic acid is only oxidized thrice in the very next paragraph. So is the solutions wrong, or am I misunderstanding what one round of beta oxidation actually amounts to?

What's the answer?

 

[Jengreef]

61 atp

 

[Captain Sisko]

61 atp

Well I've purged most of my biochem info now that class is over by if I recall correctly for each cycle you get one each of nadh fadh2 and acetyl coa. So in the end you get three nadh three fadh2 and four AcCoA. The AcCoA goes to three nadh, one fadh2, and one gtp in Krebs, and the two electron carriers go to 2.5 and 1.5 atp respectively. So each AcCoA gets you ten atp for a total of 52 atp for the eight carbon saturated fatty acid. However you use two high energy bonds to activate the free fatty acid into acyl coa. This gives you a total of 50 atp so I'm not sure where 61 comes from. My analysis hinges on the aforementioned conversions in the et chain, which are based on a given efficiency. I suppose you could plug in whatever tbr uses to get your answer, but your reasoning makes sense. Hope my nonsensical rambling helped a little.

 

[Jengreef]

well, 4 acetyl CoAs give a net 48 ATP with 12 ATP per AcCoA: 1 GTP can be converted into 1 ATP according to the book, and 11 ATP from 1 FADH and 3 NADH. 3 rounds of Beta Oxidation would give a total of 15 ATP pushing the total to 63, minus the 2 ATP cost for activating the fatty acid, thus 61. I just realized that you end up with the same amount one way or another, but it does seem TBR made a typo since the molecule really undergoes oxidation thrice, not four times.