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Topic: Determining ATP Generated from a Fatty Acid  (Read 4990 times)

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Offline Lii

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Determining ATP Generated from a Fatty Acid
« on: May 05, 2013, 03:20:39 PM »
So I'm working on a project where I need to determine the total ATP that a fatty acid would produce. I've done similar projects, but none were quite to this extent, and they were all single fatty acids. The one I'm working on now is a triacyl glycerol.

This is it: http://oi39.tinypic.com/4ftiqp.jpg

I believe a lipase would release the 3 fatty acids and I'd also end up with glycerol. So I ignored glycerol for right now and looked at the fatty acids individually, and this is what I came up with:

Each chain requires 2 ATP to enter the mitochondria.

FA1 and FA2 yield 4 Acetyl-CoA in 3 turns of beta-oxidation. FA3 yields 3 Acetyl-CoA and 1 propionyl-CoA in 3 turns of beta-oxidation.

Since 5 ATP are generated per turn, all 3 FAs generate 15 ATP each.

Propionyl-CoA goes to form succinyl-CoA, costing 1 ATP.

In the TCA cycle, 12 ATP (1 ATP directly, and 1 FADH2 = 2 ATPs, 3 NADH = 9 ATPs) are generated per Acetyl-CoA, giving 48 ATP for FA1 and FA2, and 36 for FA3.

Succinyl-CoA enters the TCA cycle and goes to form succinate, then fumerate, then malate, and finally oxaloacetate, generating a total of 5 ATP (again saying 1 GTP = 1 ATP, 1 FADH2 = 2 ATP, and 1 NADH = 3 ATP).

For all of this combined, I have a total of 175 ATP, and that's where I stopped.

For the glycerol, I was going to convert it to DHAP and send it through glycolysis. But before that, I wanted to go back through and see if I messed something up, and maybe get a second opinion?

Offline Lii

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Re: Determining ATP Generated from a Fatty Acid
« Reply #1 on: May 05, 2013, 05:00:46 PM »
Okay, I ended up working on the glycerol molecule this way:

glycerol -> g3p required 1 ATP, but g3p to dhap gave 1 NADH which gives 3 ATP.

Glycolysis starting with dhap gave 2 ATP and 1 NADH, giving a total of 5 ATP and a pyruvate.

2 ATP are required to move pyruvate into the mitochondria.

I converted the pyruvate to acetyl-CoA which yielded 1 NADH (3 ATP) and sent it though the TCA cycle, giving me another 12 ATP.

So for the glycerol I have a total of 20 ATP.
« Last Edit: May 05, 2013, 05:12:38 PM by Lii »

Offline Babcock_Hall

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Re: Determining ATP Generated from a Fatty Acid
« Reply #2 on: May 06, 2013, 12:15:48 PM »
I have not looked into all aspects of your accounting, but I have a few questions.  One is how many ATPs are you counting per NADH generated in the mitochondria.  Two is how many ATPs are you counting per FADH2 that is generated in the mitochondria.  Three is which shuttle system are you assuming for NADH that is generated in the cytoplasm.

Offline Lii

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Re: Determining ATP Generated from a Fatty Acid
« Reply #3 on: May 06, 2013, 05:34:03 PM »
3 for NADH and 2 for FADH2. And I was thinking the malate-aspartate shuttle.

Offline Babcock_Hall

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Re: Determining ATP Generated from a Fatty Acid
« Reply #4 on: May 06, 2013, 06:40:20 PM »
Those values may be a little out of date (my textbook uses 2.5 and 1.5, respectively, but I'll stick to your numbers for the sake of consistency).  IIRC in one turn of beta-oxidation, one produces two NADH and one FADH2.  Therefore, each turn of beta-oxidation gives 8 ATP.  You wrote, "Since 5 ATP are generated per turn, all 3 FAs generate 15 ATP each."  I am just not seeing how you calculated this.

Offline Lii

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Re: Determining ATP Generated from a Fatty Acid
« Reply #5 on: May 06, 2013, 07:18:11 PM »
Hm, my book is saying it produces 1 NADH and 1 FADH2.

Offline Babcock_Hall

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Re: Determining ATP Generated from a Fatty Acid
« Reply #6 on: May 06, 2013, 08:34:49 PM »
Yes, you are right with respect to the number of NADH molecules; I must have been thinking of something else.

Offline Babcock_Hall

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Re: Determining ATP Generated from a Fatty Acid
« Reply #7 on: May 06, 2013, 08:41:25 PM »

Propionyl-CoA goes to form succinyl-CoA, costing 1 ATP.

In the TCA cycle, 12 ATP (1 ATP directly, and 1 FADH2 = 2 ATPs, 3 NADH = 9 ATPs) are generated per Acetyl-CoA, giving 48 ATP for FA1 and FA2, and 36 for FA3.

Succinyl-CoA enters the TCA cycle and goes to form succinate, then fumerate, then malate, and finally oxaloacetate, generating a total of 5 ATP (again saying 1 GTP = 1 ATP, 1 FADH2 = 2 ATP, and 1 NADH = 3 ATP).
One way to deal with oxaloacetate is to convert it to PEP (via the enzyme PEP carboxykinase), and this allows for its ultimate oxidation to carbon dioxide (Zubay, Biochemistry, 4th ed., p. 340).  Otherwise it simply adds to the pool of TCA cycle intermediates.
« Last Edit: May 06, 2013, 08:56:45 PM by Babcock_Hall »

Offline Babcock_Hall

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Re: Determining ATP Generated from a Fatty Acid
« Reply #8 on: May 06, 2013, 08:56:06 PM »
Okay, I ended up working on the glycerol molecule this way:

glycerol -> g3p required 1 ATP, but g3p to dhap gave 1 NADH which gives 3 ATP.

Glycolysis starting with dhap gave 2 ATP and 1 NADH, giving a total of 5 ATP and a pyruvate.

2 ATP are required to move pyruvate into the mitochondria.
The other possibility is the flavoprotein dehydrogenase would oxidize 3-phosphoglycerol to DHAP.  This would produce FADH2, instead of NADH.

Can you explain the 2 ATPs involved in transport of pyruvate?  I am not following you there.

Offline Lii

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Re: Determining ATP Generated from a Fatty Acid
« Reply #9 on: May 07, 2013, 01:29:56 AM »
If I converted oxaloacetate to PEP wouldn't that cost 1 GTP? I'm trying to maximize ATP yield, which is also why I went the NADH route with g3p rather than the FADH2 route.

I thought I read that pyruvate required ATP to enter the mitochondria... but looking back I might have misread something.

Offline Babcock_Hall

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Re: Determining ATP Generated from a Fatty Acid
« Reply #10 on: May 07, 2013, 09:10:55 AM »
When one has anaplerotic pathways (such as propionyl CoA being converted into succinyl CoA, the question for the organism is whether or not it needs more TCA cycle intermediates.  If one has too few, the cycle will go too slowly, but if not, then the question becomes how to oxidize them completely.  If the organism converts the oxaloacetate to PEP, then it runs the PEP through glycolysis, the PDH complex and the TCA cycle.

Offline Lii

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Re: Determining ATP Generated from a Fatty Acid
« Reply #11 on: May 07, 2013, 11:54:45 AM »
Okay, so if it converts it to PEP then it'll go through the TCA cycle again, and it just keeps repeating like that?

Offline Babcock_Hall

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Re: Determining ATP Generated from a Fatty Acid
« Reply #12 on: May 08, 2013, 12:30:26 PM »
I think it is the other way around.  If you leave it as oxaloacetate, then it is a catalyst, and it will simply go around the cycle every time another acetyl CoA is added.  On the other hand, if you convert it to PEP, it becomes pyruvate, and then acetyl CoA.  Then it enters the TCA cycle and gets oxidized to carbon dioxide.

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