Fatty acid oxidation of an odd number

[deleted783484]

If we had a 17 carbon fatty acid we would get 8 acetyl coa that would follow 7 rounds of beta oxidation + 1 propionyl coa

Each round of oxidation yields 1 NADH and 1FADH2 (4ATP/round) => 4*7 rounds = 28ATP
Activation -2 ATP
8 acetylcoa => 8 rounds of TCA and each round = 10 ATP so => 80 ATP

So, from the 16 carbons => 106 ATP for 16 carbons

Now we have an additional propionyl coa that turns to succinyl coa and in the process there is loss of 1 ATP.

Now here is my question, does succinyl coa enter the TCA cycle and yield 1GTP,1 FADH2 and 1 NADH or does it not produce anything from the TCA cycle but convert back to pyruvate to undergo another TCA cycle?

Thanks!

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[yeasureyoubetcha]

If we had a 17 carbon fatty acid we would get 8 acetyl coa that would follow 7 rounds of beta oxidation + 1 propionyl coa

Each round of oxidation yields 1 NADH and 1FADH2 (4ATP/round) => 4*7 rounds = 28ATP
Activation -2 ATP
8 acetylcoa => 8 rounds of TCA and each round = 10 ATP so => 80 ATP

So, from the 16 carbons => 106 ATP for 16 carbons

Now we have an additional propionyl coa that turns to succinyl coa and in the process there is loss of 1 ATP.

Now here is my question, does succinyl coa enter the TCA cycle and yield 1GTP,1 FADH2 and 1 NADH or does it not produce anything from the TCA cycle but convert back to pyruvate to undergo another TCA cycle?

Thanks!

Think about what you're cycling. The energy equivelants are coming from the oxidation of acetyl-coA. The succinylcoA enters the TCA cycle as an intermediate as a substrate for GNG to build back to glucose. It would not convert back to pyruvate and undergo another TCA cycle. That would be regulatory mechanisms in the cell prevent this type of futile cycling. If beta oxidation is happening, you're typically in a gluconeogenic state. They glycerol head and the succinyl coA will enter as gluconeogenic precursors while the beta-oxidation provides the energy to the hepatocytes to run GNG to make glucose for the body from whatever precursor sources there are.

 

[deleted783484]

Think about what you're cycling. The energy equivelants are coming from the oxidation of acetyl-coA. The succinylcoA enters the TCA cycle as an intermediate as a substrate for GNG to build back to glucose. It would not convert back to pyruvate and undergo another TCA cycle. That would be regulatory mechanisms in the cell prevent this type of futile cycling. If beta oxidation is happening, you're typically in a gluconeogenic state. They glycerol head and the succinyl coA will enter as gluconeogenic precursors while the beta-oxidation provides the energy to the hepatocytes to run GNG to make glucose for the body from whatever precursor sources there are.

Makes sense, so now to count the net ATP from propionyl coa do I count the ATP used in gluconeogenesis?

Thanks a lot

 

[yeasureyoubetcha]

Makes sense, so now to count the net ATP from propionyl coa do I count the ATP used in gluconeogenesis?

Thanks a lot

I'm not sure anyone would ask this on an exam. Usually its just the # of ATP from beta-ox + Propionyl-CoA. If you get anything it'll probably be an even chain FA question.

If you want to count ATP's as youre trying to do, the question you ought to be asking would have to be what is the complete oxidation of the fatty acid. You wouldn't need to factor in the cost of 4 ATP from GNG in this case. I was just pointing out that in the case of beta oxidation feeding GNG, when the propionyl coa enters the TCA as succinyl coA there are 2 fates: remain a TCA intermediate in the mitochondria, or get built up into glucose.