Total Energy from Fatty Acids: Study with Video Lessons, Practice Problems & Examples

The total ATP yield from the complete oxidation of a fatty acid involves several key processes. Initially, fatty acid activation incurs a cost of 2 ATP. During one cycle of beta-oxidation, 1 FADH₂ and 1 NADH are produced, along with 1 Acetyl CoA. In the citric acid cycle, 1 Acetyl CoA generates 1 ATP, 1 FADH₂, and 3 NADH. The total ATP from oxidative phosphorylation is calculated as 12 ATP, considering the contributions from NADH and FADH₂. This highlights the efficiency of fatty acid metabolism in energy production.

Total Energy from Fatty Acids Concept 1

Hey, everyone. So in this video, we'll take a look at the total energy from fatty acids. Now here we're going to say to calculate the total ATP yield from the complete oxidation of a fatty acid, we must consider two things. First, we need to consider the ATP from Acetyl CoA oxidation within the citric acid cycle or Krebs cycle. In addition to this, we need to think about ATP from NADH and FADH₂, our two high energy molecules that are in oxidative phosphorylation. Now if we take a look here, we're looking at this in relation to one cycle of beta oxidation. We're looking at Krebs cycle and oxidative phosphorylation. Our starting materials here, we're starting with our fatty acid. Remember, we have to have fatty acid activation, which is a one-time expense of 2 ATP. So here this would actually be minus 2. We'd say that we would have the generation of 1 FADH₂ and 1 NADH, because that happens for every cycle we make one of each. And then we would have the creation of 1 Acetyl CoA since we're only going through one cycle of beta oxidation. Now for Krebs cycle here, we have that 1 acetyl CoA, and we would say that we would have the generation of 1 ATP, 1 FADH₂, and 3 NADH. Remember, normally when we do glucose, we have the formation of 2 acetyl CoA's, so these numbers will be double. But here, since we're only dealing with one Acetyl CoA, we only have half of each of these amounts. We would have our end molecule as oxaloacetate. Now here, moving on towards oxidative phosphorylation, we have the dropping off electrons by NADH and FADH₂. So we wouldn't generate any of them. We would have the reduction of oxygen into water as our end molecule, but how much ATP would be involved? Well, we can see that we have a total of 2 NADH's. 1 from beta oxidation and one from Krebs cycle. And we have 4 NADH's. Remember that NADH is 2.5 ATP, so times 4 would give me 10. And then we'd have 2 FADH₂'s, each one is 1.5 ATP, so that's 3 ATP, for a total of 13 ATP molecules. Now adding everything across the board, we'd have minus 2, plus 1, plus 13, that'd give us a total of 12 ATP. And then we'd have 1 plus 1 is 2, and 1 plus 3 is 4. Remember, when we talk about Krebs cycle and oxidative phosphorylation, these are termed our common metabolic pathways. Alright. So this was the total that we would get for each one of these in terms of ATP, FADH₂, and NADH. So keep this in mind when we take a look at the total energy involved with fatty acids.

Total Energy from Fatty Acids Example 1

Here in this example question, it says, calculate the total ATP yield from the complete beta oxidation of myristic acid. Here, this represents a 14 Carbon Atom Fatty Acid. So here, the way we start is we're going to say step 1, we have to calculate the number of cycles of beta oxidation. Now remember, your number of cycles is number of carbons of the fatty acid divided by 2, minus 1. So, here we have a 14 carbon fatty acid divided by 2 minus 1, so that'd be 7 minus 1, so we'd have 6 cycles.

Next, we're going to calculate the total number of NADH and FADH₂ produced during beta oxidation. This is equal to the number of cycles. Because we have 6 cycles that means we're going to have 6 NADH's and 6 FADH₂s.

Next, we have to calculate the total ATP, NADH, and FADH₂ produced during the Citric Acid Cycle. Now, here this depends on the number of Acetyl CoA molecules from beta oxidation. Remember the number of Acetyl CoA is equal to the number of carbons of your fatty acid divided by 2. So, it'll be 14 divided by 2, so that means we'd have 7 Acetyl CoAs. So, here, we have 7 Acetyl CoAs. We would say that would be 7 times 1 for 7 ATP. We'd have 7 times 3 which gives me 21 NADH's. And then, we would say here, 7 times 1, which would give me 7 FADH₂s. Remember, this number of 3 and 1 for NADH and FADH₂, we talked about that in the very beginning when it came to the amount of total energy evolved from a fatty acid oxidation. If you don't see that, go back to the previous video to see those values.

Now, here we have to convert our total number of NADH and FADH₂ to ATP from Oxidative Phosphorylation. Now remember, 1 NADH is equal to 2.5 ATP. 1 FADH₂ is equal to 1.5 ATP. So based on our numbers here, what are we going to do? We're going to say here that we got, 21 NADH's here from the citric acid cycle. And then, also remember we have another 6 NADH's here based on the number of cycles when it comes to beta oxidation. So we'd have 6 + 21 which gives me 27 NADH's. We multiply that by 2.5 ATP which would give me 67.5 ATP total based on NADH. Now, here we have 7 FADH₂'s from the Citric Acid Cycle and then another 6 that we got from Beta Oxidation based on the number of cycles. So that'd be 6 plus the 7, so that'd give me 13 FADH₂. Remember each one is 1.5 ATP, so that give me 19.5 ATP.

Then we're going to say, add all the ATP's and remember there is a one-time expense of 2 ATP involved. So here we'd add up the 67.5 ATP plus the 19.5 ATP minus the one-time cost of 2 ATP, that would give me 85 ATP total. So 85 would be the total amount of our ATP yield when we're talking about the complete beta oxidation of this 14 Carbon Atom Fatty Acid.

Rank the following molecules based on amount of energy stored in them in increasing order (per mol).

I. Sucrose                           II. Arachidic                         III. Glucose                         IV. Behenic (22:0)

• A. I, III, II, IV
• B. III, I, II, IV
• C. II, IV, III, I
• D. IV, II, I, III

Provide total moles of ATP produced by complete β-oxidation of 3.4 g of palmitic acid (256.43 g/mol).

• A. 1.4 ATP
• B. 31.2 ATP
• C. 106 ATP
• D. 1.43 ATP

Here’s what students ask on this topic:

How is the total ATP yield from fatty acid oxidation calculated?

The total ATP yield from fatty acid oxidation is calculated by considering several key steps. First, fatty acid activation costs 2 ATP. During one cycle of beta-oxidation, 1 FADH₂ and 1 NADH are produced, along with 1 Acetyl CoA. In the citric acid cycle, 1 Acetyl CoA generates 1 ATP, 1 FADH₂, and 3 NADH. The total ATP from oxidative phosphorylation is calculated by converting NADH and FADH₂ into ATP. Each NADH yields 2.5 ATP and each FADH₂ yields 1.5 ATP. Summing these contributions gives the total ATP yield.

What is the role of Acetyl CoA in the citric acid cycle during fatty acid oxidation?

Acetyl CoA plays a crucial role in the citric acid cycle during fatty acid oxidation. Each Acetyl CoA enters the citric acid cycle and generates 1 ATP, 1 FADH₂, and 3 NADH. These high-energy molecules are then used in oxidative phosphorylation to produce ATP. The citric acid cycle is essential for converting the energy stored in Acetyl CoA into a form that can be used by the cell, highlighting its importance in energy metabolism.

How many ATP molecules are produced from NADH and FADH₂ during oxidative phosphorylation?

During oxidative phosphorylation, each NADH molecule produces 2.5 ATP, and each FADH₂ molecule produces 1.5 ATP. For example, if you have 4 NADH molecules, they will produce 10 ATP (4 x 2.5). Similarly, if you have 2 FADH₂ molecules, they will produce 3 ATP (2 x 1.5). These conversions are crucial for understanding the total ATP yield from fatty acid oxidation.

What is the initial ATP cost for fatty acid activation?

The initial ATP cost for fatty acid activation is 2 ATP. This activation step is necessary to prepare the fatty acid for subsequent beta-oxidation. Although it incurs an energy cost, it is essential for the efficient breakdown and utilization of fatty acids in energy metabolism.

Why is fatty acid metabolism considered efficient in energy production?

Fatty acid metabolism is considered efficient in energy production because it generates a high yield of ATP. Each cycle of beta-oxidation produces 1 FADH₂ and 1 NADH, which are converted into ATP during oxidative phosphorylation. Additionally, the citric acid cycle generates further ATP, FADH₂, and NADH from Acetyl CoA. Despite the initial ATP cost for activation, the overall process yields a significant amount of ATP, making it a highly efficient energy source.