How to calculate ATP yield: Difference between revisions

To calculate the exact ATP yield you must know your MRTs (specifically, the reactions related to glycolysis), because you need to follow the pathway from the starting compound all the way until it’s broken down into NADH and FADH2. These electron carriers will enter the mitochondria and produce ATP by oxidative phosphorylation. One molecule of NADH yields 2,5 ATP and one molecule of FADH2 yields 1,5 ATP. You also need to know that each acetyl-CoA yields 10 ATP in the TCA cycle.

In the TCA cycle one acetyl-CoA yields 3 NADH, 1 FADH2 and 1 GTP. GTP is equivalent to ATP so we count it as an ATP. 3 x 2,5 + 1 x 1,5 + 1 = 10 ATP total.

=== ATP yield of glucose ===

Let’s start with the simplest. Glucose is metabolised through the glycolysis into 2 acetyl-CoA, which will then go through the TCA cycle.

Glucose is first converted to glucose 6-phosphate. This requires 1 ATP, which we need to subtract from the total in the end. Glucose 6-phosphate is converted into fructose 6-phosphate, which doesn’t consume or produce ATP. Currently we are at a yield of -1 ATP.

Each pyruvate is converted to acetyl-CoA, which yields 1 NADH each. The yield is now -2 + 2 + 2 ATP and 2 + 2 NADH.

So, then we must add everything together. The reactions forming 2 acetyl-CoA from glucose have yielded -2 + 2 + 2 = 4 ATP and 4 NADH. Then, the 2 molecules of acetyl-CoA enter the TCA cycle and yield 3 NADH, 1 FADH2 and 1 ATP each.

This gives 4 ATP + 2 ATP, 4 + 6 NADH, and 2 FADH2, a total of 6 ATP, 10 NADH, and 2 FADH. 10 NADH = 25 ATP and 2 FADH2 = 3 ATP. 4 ATP + 25 ATP + 3 ATP gives 32 ATP, which is the ATP yield of one molecule of glucose.

=== ATP yield of glycolysis intermediates ===

For example, the ATP yield of glucose 6-phosphate is 32 – (-1) = 33 ATP, because glucose 6-phosphate doesn’t need to be phosphorylated and therefore doesn’t need the 1st ATP from above.

The ATP yield of fructose 1,6-bisphosphate is 32 – (-2) = 34 ATP.

When considering the ATP yield of phosphoenolpyruvate it’s important to remember that only one molecule of acetyl-CoA is produced, in contrast to during the breakdown of glucose. The ATP yield of PEP is 1 ATP + 1 NADH + 3 NADH + 1 FADH2 + 1 ATP = 1 + 1 x 2,5 + 3 x 2,5 + 1 x 1,5 + 1 = 13,5 ATP.

=== ATP yield of fatty acids ===

When considering the ATP yield of fatty acids it’s important to remember that for a fatty acid to enter beta oxidation a -CoA group must be attached to this fatty acid. This process (MRT 43) converts 1 ATP to 1 AMP, which is equal to consuming 2 ATP. In other words, the ATP yield of for example hexanoate is 2 ATP less than the yield of hexanoyl-CoA.

Beta-oxidation works in cycles. Each cycle of the beta-oxidation will make the fatty acid 2 carbons shorter, but it will yield 1 NADH, 1 FADH2 and 1 acetyl-CoA. Those 2 carbons the fatty acid lost are converted into acetyl-CoA. The fatty acid which is now 2 carbons shorter than the one we started with will enter the beta-oxidation, which will yield 1 NADH, 1 FADH2, 1 acetyl-CoA and a fatty acid which is 4 carbons shorter than the one we started with, and so on.

When the fatty acid is only 4 carbons long it will undergo its last round of beta-oxidation, and yield 1 NADH, 1 FADH2 and 2 acetyl-CoA.

Let’s do hexanoate as an example. The activation of hexanoate to hexanoyl-CoA requires 2 ATP, which we must keep in mind.

Beta-oxidation works in cycles. Hexanoyl-CoA will first undergo one cycle of beta-oxidation, which yields 1 NADH, 1 FADH2 and 1 acetyl-CoA, and the hexanoyl-CoA, which has lost 2 carbons, is now 4 carbons long and is therefore a butyryl-CoA.

Butyryl-CoA will undergo another cycle of beta-oxidation, yielding 1 NADH, 1 FADH2 and 2 acetyl-CoA.

In total we have 3 acetyl-CoA, each of which give 3 NADH, 1 FADH2 and 1 ATP. So the 3 acetyl-CoA give us 9 NADH, 3 FADH2 and 3 ATP.

We have undergone 2 beta-oxidation, each of which have yielded 1 NADH and 1 FADH2.

In total we have 9 NADH + 2 NADH = 11 NADH, 3 + 2 = 5 FADH2 and 3 ATP. This gives us 11 x 2,5 + 5 x 1,5 + 3 = 38 ATP. However, we mustn’t forget that we consumed 2 ATP when activating the fatty acid in the first place. So the total yield becomes 36 ATP.

=== ATP yields of ketone bodies ===

Acetoacetate is then converted into acetoacetyl-CoA by ''β-ketoacyl-CoA transferase'', which doesn’t require energy. Acetoacetyl-CoA is then converted into 2 acetyl-CoA by ''thiolase''.

=== Arsenate poisoning ===