Fatty Acid Oxidation Practice 1 - Online Tutor, Practice Problems & Exam Prep

In fat catabolism, glycerol enters metabolism as dihydroxyacetone phosphate (DHAP), converting to glyceraldehyde 3-phosphate (G3P). Carnitine is crucial for transporting fatty acids into the mitochondrial matrix via the carnitine shuttle, involving Carnityl Acetyltransferase 1. Beta oxidation follows a specific enzyme order: acetyl CoA dehydrogenase, enoyl CoA hydratase, beta hydroxyacyl CoA dehydrogenase, and thiolase. Palmitic acid yields 108 ATP, while palmitoleic acid, with one unsaturation, generates approximately 106 ATP due to reduced FADH2 production.

Fatty Acid Oxidation Practice 1

In the catabolism of fat, glycerol will enter metabolism as dihydroxyacetone phosphate or DHAP. This will be converted to glyceraldehyde-3-phosphate or G3P, and you know the story from there. Now, carnitine is essential for intracellular transport of fatty acids. The carnitine shuttle is how fatty acids are going to get into the mitochondrial matrix. That is going to combine with carnitine thanks to Carnitine Acyltransferase 1. That is going to be exported into the matrix. At the same time, this transporter is actually an antiport, and it's going to transport out carnitine while it brings this molecule in. Once inside, the carnitine is going to be removed from the fatty acyl CoA, and it's going to be exported back out to bring another fatty acyl attached to carnitine in. So, moving on, what is the correct order of enzymes in beta oxidation? Well, the first thing that's going to happen is acyl CoA dehydrogenase is going to oxidize our molecule and it's going to generate an FADH₂. From there, the enoyl CoA hydrolase is going to act on that, and it's going to produce an alcohol group. From there, we are going to have beta hydroxyacyl CoA dehydrogenase, which is going to oxidize our alcohol group and it's going to generate an NADH. And then, lastly, thiolase is going to cut off our acetyl CoA. All right. So the correct order is acyl CoA dehydrogenase, enoyl CoA hydrolase, beta hydroxyacyl CoA dehydrogenase, and thiolase.

Now, the conversion of 1 palmitic acid through beta oxidation and the citric acid cycle, converting all of the molecules into ATP, all of those electron carriers to ATP, how much ATP do we get? The answer is 108. I'm not going to explain it here because I already did. We're dealing with palmitoleic acid, which is going to have 1 degree of unsaturation. How much ATP are we going to generate? Well, remember that if we have a degree of unsaturation, in this case just 1, right? There's going to be no need for reduction with NADPH. So just 1 degree of unsaturation means we're not going to be generating 1 FADH that we did in the previous problem. So in the previous problem, we were dealing with a totally saturated fatty acid. Now we have 1 degree of unsaturation, meaning we're going to produce one less FADH, meaning we're going to generate about 1.5 less ATPs. The closest whole number answer here is B, 106. That's how many ATPs we'll generate in total. I guess technically you could say it's 106.5, but you can't make half an ATP. You have to round, and this is the closest number as an answer choice.

All right. Let's flip the page.

Here’s what students ask on this topic:

What is the role of carnitine in fatty acid oxidation?

Carnitine plays a crucial role in the transport of fatty acids into the mitochondrial matrix, where β-oxidation occurs. The carnitine shuttle system involves Carnityl Acetyltransferase 1, which facilitates the binding of fatty acids to carnitine. This complex is then transported into the mitochondrial matrix via an antiport mechanism, which simultaneously exports carnitine out of the matrix. Once inside, carnitine is removed from the fatty acyl-CoA, allowing the fatty acid to undergo β-oxidation. The carnitine is then recycled back to the cytosol to transport another fatty acyl group.

What is the correct order of enzymes involved in β-oxidation?

The correct order of enzymes involved in β-oxidation is as follows: First, acetyl-CoA dehydrogenase oxidizes the fatty acyl-CoA, generating FADH₂. Next, enoyl-CoA hydratase adds a water molecule, forming an alcohol group. Then, β-hydroxyacyl-CoA dehydrogenase oxidizes the alcohol group, producing NADH. Finally, thiolase cleaves the acetyl-CoA from the fatty acyl chain. This sequence ensures the systematic breakdown of fatty acids into acetyl-CoA units, which can then enter the citric acid cycle for further energy production.

How much ATP is generated from the complete oxidation of palmitic acid?

The complete oxidation of one molecule of palmitic acid (C₁₆H₃₂O₂) through β-oxidation and the citric acid cycle generates a total of 108 ATP molecules. This includes ATP produced from NADH and FADH₂ generated during β-oxidation and the citric acid cycle, as well as ATP directly produced in the cycle. The breakdown is as follows: 7 FADH₂ (7 x 1.5 ATP), 7 NADH (7 x 2.5 ATP), and 8 acetyl-CoA (8 x 10 ATP), totaling 108 ATP.

How does the presence of unsaturation in fatty acids affect ATP yield during β-oxidation?

The presence of unsaturation in fatty acids reduces the ATP yield during β-oxidation. For example, palmitoleic acid, which has one degree of unsaturation, generates approximately 106 ATP instead of 108 ATP. This reduction occurs because the unsaturation bypasses the first dehydrogenation step, resulting in the production of one less FADH₂. Since each FADH₂ yields approximately 1.5 ATP, the total ATP yield is reduced by this amount, leading to a final count of around 106 ATP for palmitoleic acid.

What is the significance of glycerol in fat catabolism?

In fat catabolism, glycerol is a significant byproduct that enters the metabolic pathway as dihydroxyacetone phosphate (DHAP). DHAP is then converted to glyceraldehyde 3-phosphate (G3P), which can enter glycolysis or gluconeogenesis. This conversion allows the glycerol component of triglycerides to be utilized for energy production or glucose synthesis, making it an important link between lipid metabolism and carbohydrate metabolism.