Fatty Acid Oxidation Practice 2: Videos & Practice Problems

In beta oxidation, the presence of coenzyme A (CoA) is crucial for the conversion of fatty acids into acetyl CoA. An odd number of carbons in fatty acids requires careful consideration during oxidation, resulting in the production of propanoyl CoA. Each round of beta oxidation generates reduced electron carriers: 4 NADH and 2 FADH₂, leading to a total ATP yield of 52 after accounting for the ATP spent in the conversion to succinyl CoA. NADPH is essential for reducing specific carbon-carbon double bonds due to their conformation.

Fatty Acid Oxidation Practice 2

So, which compound here is an intermediate of beta oxidation? This one's a little tricky. The answer is d and if you look at d notice how you have your coA on the end which you need, right? You need your coA there. So based on just that, you can eliminate all of these, right? So only these 2 have the coA, right? But now, this one, this one has this oxygen here. I don't know what that's all about, right? So, that's out. Also, let's just take a closer look at D. D is basically our final round of beta oxidation, right? D is going to be our last round of beta oxidation because look, if we cut it in half there, we're going to be left with 2 acetyl CoA's. You have one here because that's going to get a coA attached to it and then you have your other already formed right there.

Now, let's take a look at this molecule. Why does this molecule require NADPH to reduce a carbon carbon double bond during beta oxidation? Well, the answer is because of this particular conformation of double bonds that it has. So, it's because of the conformation of double bonds and I don't think you need to really bother like knowing exactly what that conformation is that's going to require NADPH. But just know that NADPH is used to reduce a carbon carbon double bond during beta oxidation due to specific conformation of 2 double bonds, carbon carbon double bonds.

Now, let's take a look at this last problem here. Consider the beta oxidation of the following fatty acid. Alright. How many rounds of beta oxidation are we going to have to do here? Well, first, let's start by just looking at how many carbons we have here. So, if you count up your carbons, you hopefully will see that we actually have 11. Right? 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. Right? So we have an odd number of carbons. So we already know that this is going to be a little trickier than normal. So let's put in our cut points. We're going to cut there, there, there, there. And we do have these double bonds present but they're not next to each other. So we're not going to have a situation where we can't just use an isomerase to move the double bond around to get it into the right place, right? That only comes up when we have double bonds that are next to each other. So, that's not going to happen here.

Now, how many rounds of beta oxidation are necessary to convert it to Acetyl CoA? Well, only 4, right? Four rounds. But caveat, we are going to have to do something about this because that's going to come off as propionyl CoA, right? So let's think of the output of reduced electron carriers and ATP. Alright. So, looking at this, this is going to generate directly 1, 2, 3, 4 Acetyl CoA, right? Because this is going to go off to succinyl CoA. And we don't know what's going to happen to that. So I'm just going to rule that out, right? We don't know what's going to happen to the succinyl CoA. It could be used for other stuff. So who knows with that? But we know for sure that we're going to be generating 1, 2, 3, 4 Acetyl CoAs.

So, what's going to be the output here? Alright. Well, let's think about this. We are doing 4 rounds of beta oxidation. So that normally would mean 4 FAD, right? But we have these two points of unsaturation. So we're only going to have 2 FADH₂. We are going to have 4 NADH. And of course this is going to lead to 3 ATP and this is going to lead to 10 ATP. And now let's think about our acetyl coases, right? They're going through the citric acid cycle and those 4 coases are going to make 4 FADH₂ and those 4 acetyl CoAs are going to make 12 NADH. So, again, FADH₂ that is going to be 1.5 ATP. We're going to make 6 ATP with this. 6 ATP and then NADH 2.5. So this is going to be 30 ATP. And then don't forget that we're also going to produce 4 GTP ATP. I'm going to count them in. 4 of those. Now there's one thing. One thing. We can't add this all up yet because in producing the succinyl CoA, we have to spend minus 1 ATP, right? We have to spend 1 ATP to make that. So let's total it up right now. So we are going to add all of this together and if we do, we get 52 ATP total. Because again, the issue here is that we're going to lose 1 ATP, in making succinyl CoA. So normally, this would actually all add up to 53 but we have to subtract that 1 ATP to make succinyl CoA. So 52 ATP total.

All right. That's all I have for this exam review. Good luck studying for your test. If you have any questions, please post them in the forum.

Here’s what students ask on this topic:

What is the role of Coenzyme A (CoA) in beta oxidation?

Coenzyme A (CoA) plays a crucial role in beta oxidation by forming a thioester bond with fatty acids, converting them into acyl-CoA derivatives. This activation step is essential for the fatty acid to enter the beta oxidation pathway. CoA ensures that the fatty acid is sufficiently reactive for subsequent enzymatic reactions, ultimately leading to the production of acetyl-CoA, which enters the citric acid cycle for further energy production.

How does the presence of an odd number of carbons in fatty acids affect beta oxidation?

Fatty acids with an odd number of carbons undergo beta oxidation similarly to even-numbered fatty acids until the final three-carbon fragment, propanoyl-CoA, is produced. Propanoyl-CoA is then converted to succinyl-CoA, which enters the citric acid cycle. This additional step requires the expenditure of 1 ATP, slightly reducing the overall ATP yield compared to even-numbered fatty acids.

Why is NADPH required during beta oxidation of certain fatty acids?

NADPH is required during the beta oxidation of certain fatty acids to reduce specific carbon-carbon double bonds. This reduction is necessary due to the unique conformation of these double bonds, which cannot be processed by the usual enzymes involved in beta oxidation. NADPH provides the reducing power needed to convert these double bonds into a form that can be further oxidized.

How many ATP molecules are produced from the complete beta oxidation of a fatty acid with 11 carbons?

The complete beta oxidation of an 11-carbon fatty acid involves four rounds of beta oxidation, producing 4 acetyl-CoA, 4 NADH, and 2 FADH₂. The acetyl-CoA enters the citric acid cycle, generating additional ATP. The total ATP yield is 52, accounting for the ATP spent in converting propanoyl-CoA to succinyl-CoA.

What are the main products of each round of beta oxidation?

Each round of beta oxidation produces one molecule of acetyl-CoA, one NADH, and one FADH₂. Acetyl-CoA enters the citric acid cycle, while NADH and FADH₂ are used in the electron transport chain to generate ATP. The process continues until the entire fatty acid is converted into acetyl-CoA units.