Oxidation of Fatty Acids: Study with Video Lessons, Practice Problems & Examples

Fatty acid oxidation involves three key phases: activation, transport, and beta oxidation. Activation consumes energy, converting fatty acids to fatty acyl CoA via acyl CoA synthetase, utilizing ATP. Transport requires carnitine to shuttle fatty acyl groups across the mitochondrial membrane. Beta oxidation cleaves fatty acids into Acetyl CoA, producing FADH₂ and NADH in cycles. Each cycle shortens the fatty acid chain by two carbons, with the overall energy output depending on the fatty acid's carbon count, accounting for a one-time ATP cost and yielding multiple Acetyl CoA molecules.

Oxidation of Fatty Acids Concept 1

In this video, we'll take a look at the first phase when it comes to fatty acid oxidation. Now, phase A is our activation step. We're going to say similar to glycolysis, fatty acid activation is an energy-consuming step. The enzyme that we have to utilize is our acyl CoA synthetase. Here, it catalyzes the conversion of fatty acid to fatty acyl CoA. Now, when it comes to a synthetase, this is an enzyme that catalyzes a synthesis reaction. And unlike a synthase, this requires energy from ATP. Alright. So that's the difference between the two. This one here would not. Now, here we have one ATP is hydrolyzed to 1 AMP and 2 inorganic phosphates. So, this is equivalent to having 2 ATP becoming ADP2. If we look at our overall reaction here, we have our fatty acid which is going to become activated, we have our coenzyme A here with its thiol group exposed, ATP becomes AMP because we require 2 inorganic phosphates being produced. Again, we're using our synthetase enzyme to do this, and then here is our activated fatty acid as a product. So just remember, phase A is activation when it comes to fatty acid oxidation.

Oxidation of Fatty Acids Concept 2

Now the second phase of fatty acid oxidation is our transport phase. Here we're going to say that our fatty acyl CoA cannot directly cross the mitochondrial membrane. So if we take a look at this image here, we have our cytosol, we have our mitochondrial membranes, and once we get past that, we enter the mitochondrial matrix. Here, we're going to say, here is our fatty acyl CoA, it cannot traverse across the mitochondrial membrane. So, to do this, we're going to introduce carnitine here. It's the enzyme Carnitine Acyl Transferase that transfers the fatty acyl group from CoA to carnitine. So here we see that CoA has now been replaced. Well, this whole thing here has been replaced with our Carnitine. Now that we have Carnitine, it can traverse across the mitochondrial membrane. It has now entered the mitochondrial matrix.

You're going to say the fatty acyl carnitine moves from the cytosol to the mitochondrial matrix. The fatty acid carnitine reacts with CoA in the mitochondrial matrix to produce fatty acyl CoA. So here, once the carnitine has moved into the matrix, it reacts with this coenzyme A here with its thiol group, thus creating our fatty acyl CoA that we needed. Carnitine is released in the process and it's free to exit the mitochondrial matrix, pass through the mitochondrial membrane back into the cytosol to begin again. It can then react if it wants to with another fatty acyl CoA and start the process again. Alright. So, just remember, when it comes to transporting here it's us converting our fatty acyl CoA into Carnitine, and we're using a Carnitine shuttle to move from the cytosol to the mitochondrial matrix by crossing the mitochondrial membranes.

Oxidation of Fatty Acids Example 1

In this example, it says fatty acid activation requires hydrolysis while we have one ATP going to 1 AMP. How is this equivalent to 2 ATP to 2 ADP? Alright. So, here, we're going to say 1 AMP molecule carries an amount of energy equivalent to 2 ADP molecules. No. That's not true because this one will only have 1 energetic bond. Here, this would have 2 ADP molecules which is 4 energetic bonds so that's not equivalent. Conversion of 1 ATP to 1 AMP requires cleavage of 2 high-energy phosphoanhydride bonds, that is true. Here we have triphosphate and this is only monophosphate. We've lost 2 phosphates here. So that means we'd have to cut 2 high-energy phosphoanhydride bonds to do this.

Hydrolysis of ATP to AMP is accompanied by the oxidation of an electron carrier such as NADH. Here, we're not talking about oxidation in this state. We're talking about basically the cleaving of our phosphoanhydride bonds. This has nothing to do with oxidation. So, this would not work. And then option D doesn't work either. We found out that option B is the most reasonable answer in terms of this.

Oxidation of Fatty Acids Concept 3

In this video, we'll take a big picture look at phase c oxidation when it comes to fatty acid oxidation. Here, we're going to say that the beta oxidation pathway consists of 4 repeated reactions. We're going to say, it cleaves 2 carbons. So we're going to have Acetyl CoA from the fatty acid chain in each cycle. We're going to say here, one cycle of the pathway produces 1 FADH₂, 1 NADH, and 1 Acetyl CoA. If we take a look here, we have our fatty acid. We undergo these repeated reactions. So one cycle here, we produce FADH₂ and NADH as our energy molecules, high energy molecules. We're going to create Acetyl CoA over here, so 2 carbons. Notice that we started out with 2, 4, 6, 8 carbons here.

But my fatty acid chain is now only 6 because 2 of them are part of Acetyl CoA over here. So what I've done is I've shortened my fatty acid chain. So we have our fatty acid, we've shortened it through oxidation to produce Acetyl CoA, and then because we still have additional carbons on this chain we could go through additional cycles. Here, we're looking at just one cycle though. We are creating 1 FADH₂, 1 NADH, we're creating 1 Acetyl CoA, and we have this shortened fatty acid.

Oxidation of Fatty Acids Concept 4

In this video, we're going to take a look at Beta Oxidation number 1. Here we're going to say the enzyme Acyl CoA dehydrogenase removes 2 Hydrogen atoms from Alpha and Beta Carbon atoms. As a result of this, we're going to create a double bond between the Alpha and Beta Carbon atoms. Now, we're also going to utilize FAD in order to do this. It's going to be reduced in the process to create FADH2. If we take a look here we have our fatty acyl CoA. Remember the carbonyl group is this C = O. The carbon next to it is the alpha carbon. And the carbon next to the alpha carbon is the beta carbon. Here we have FAD which gets reduced to FADH2. We utilize our enzyme Acyl CoA dehydrogenase. As a result of this, we create our Trans Enoyl CoA, the Hydrogens would orient themselves trans to one another, so that's why it's Trans Enoyl CoA. So this would be what we produce in beta oxidation number 1 in phase c of fatty acid oxidation.

Oxidation of Fatty Acids Concept 5

In this video, we're going to take a look at the hydration step. Here, we're going to say that the enzyme Enoyl CoA Hydratase adds water to the alpha beta double bond. Here, it's going to place the hydroxyl group or OH group at the beta carbon. As a result of this, we're going to say 3-Hydroxy Acyl CoA is produced. So here's our trans enol CoA, hydratase helps to add water, so water is going to come in. The water is split where the beta carbon gets the OH group, and the alpha gets the H. Here, if we were to number this, the carbonyl carbon would be 1, this would be 2, and the beta carbon would be carbon number 3. That's why the name is 3-hydroxy. The OH group is on the beta carbon which also serves as carbon number 3. Right? So this would represent what we produce in the hydration step of basic oxidation when it comes to fatty acid oxidation.

Oxidation of Fatty Acids Example 2

Here it says we need to identify the alpha and beta carbon atoms in the structure below and complete the reaction. So, here is our carbonyl group. Next to it is the alpha carbon. That carbon would have 2 hydrogens. Next to the alpha would be our beta carbon which also has 2 hydrogens. Over here, we have our carbonyl connected to our SCoA. The alpha carbon would still have 1 hydrogen and it loses 1. To continue making 4 bonds, it'd have to form a double bond with the beta carbon, which also loses 1 hydrogen. Remember to show them trans to one another. And then, that beta carbon is still connected to this methyl group over here. So, this will represent our product when it comes to the utilization of Acyl CoA dehydrogenase. Now, remember we'd also have to use FAD here, so that it becomes FADH₂ in order to create this trans product here. Alright. So, that's what we'd say in terms of the alpha and beta carbons and the product formed.

Oxidation of Fatty Acids Concept 6

In this video, we're going to take a look at beta oxidation number 2. Here, the enzyme 3 Hydroxy CoA dehydrogenase catalyzes the oxidation of the beta hydroxyl group. Now, here since we're oxidizing that hydroxyl group, it's going to form a ketone at the beta carbon. We're going to say in this process of oxidation we're going to utilize NAD⁺, it gets reduced to NADH. So if we take a look here, we have 3 Hydroxy Acyl CoA. We utilize our enzyme 3 Hydroxy Acyl CoA dehydrogenase. Remember, the enzyme name is just the substrate followed by the class of enzyme. Since this is an oxidation, we're utilizing dehydrogenase. We're using NAD⁺ in order to oxidize our substrate. In the process, it gets reduced to NADH. Now, what happens here is we have this alcohol group and we oxidize a secondary alcohol we make a ketone. So now it is a ketone group. And we're going to say here because it is a ketone it becomes a keto acyl CoA. And because it's on the beta carbon, it becomes more specifically a beta-ketoacyl CoA as our product for beta oxidation number 2.

Oxidation of Fatty Acids Example 3

Identify each of the following statements about beta oxidation as true for t or false f. Hydration of trans enoyl CoA in the second reaction of beta oxidation produces 3-hydroxyacyl CoA. Here, that is true. The formation of beta-ketoacyl CoA from the oxidation of 3-hydroxyacyl CoA requires NAD⁺ as the coenzyme. Yes. That is also true. It is an oxidation, so we're utilizing dehydrogenase, but in order to help with facilitating the oxidation, we do use NAD⁺. NAD⁺ becomes NADH when it gets reduced. Bond cleavage to produce an acetyl CoA from beta-ketoacyl CoA is catalyzed by beta-ketoacyl CoA thiolase. Here, that is also true. Finally, oxidation of the fatty acyl CoA by FADH₂ produces a cis double bond between alpha and beta carbon atoms. That's false. It doesn't create a cis double bond, it creates a trans double bond. So out of these statements, only the fourth one, the last one, is a false statement. The previous three are true.

Which one of the following coenzymes is not a part of the β-oxidation pathway?

• A. ATP
• B. FADH₂
• C. CoQ
• D. CoA
• E. NADH

Oxidation of Fatty Acids Concept 8

In this video, we'll take a look at the Beta oxidation energy output. Here, we're going to say that the energy output of the Beta oxidation depends on the number of carbon atoms in the fatty acid. And, we're gonna say fatty acid activation has a one-time expense of 2 ATPs. And, we're gonna say each cycle cleaves 2 carbons. In addition to this, we're gonna say that for every one cycle we'll have 1 FADH₂ and 1 NADH as our high energy molecules that are produced. If we take a look here we have our fatty acid, remember we have a one-time expense of 2 ATPs in order to activate it, this will transform it into my fatty acyl CoA.

In terms of a formula we could talk about the number of cycles involved, that's just the number of carbons divided by 2 minus 1. In this example here, we're gonna do 3 cycles. Each cycle produces 1 FADH₂ and 1 NADH. And since we have 3 cycles, we're gonna make 3 of each. Now, the number of Acetyl CoA that we would make is equal to the number of carbons divided by 2. This particular fatty acid has 8 carbon atoms. So, we do 8 divided by 2, so we should make 4 Acetyl CoA's.

From this, we can fill out this chart on the right, so 3 cycles of beta oxidation. We're gonna say again there's a cost, one-time cost of 2 ATPs. We're doing 3 cycles, so we should make 3 FADH₂s and 3 NADH's. Since this is an 8 Carbon Fatty Acyl CoA molecule, it'd be 8 divided by 2 giving us 4 Acetyl CoA's as our end molecule. So remember, this is just the setup when we talk about the energy output, the energy cost when it comes to beta oxidation.

Oxidation of Fatty Acids Example 4

Here in this example question, it says bionic acid is a long chain fatty acid containing 22 carbon atoms. How many cycles of beta oxidation are required to completely degrade bionic acid? Alright. So here, they're asking us for the number of cycles. Now, recall, if we're talking about the number of cycles, well, that's just equal to the number of carbons divided by 2 minus 1. We have 22 carbons involved, divided by 2 minus 1. That'd be 11 minus 1, which means it would take 10 cycles to completely degrade this particular fatty acid. So, that would mean the answer would have to be option A, 10 cycles.

How many total FADH₂, NADH, and acetyl CoA molecules will be produced when stearic acid undergoes β‑oxidation?

• A. 10 FADH₂, 10 NADH, and 9 acetyl CoA
• B. 9 FADH₂, 9 NADH, and 9 acetyl CoA
• C. 8 FADH₂, 8 NADH, and 8 acetyl CoA
• D. 8 FADH₂, 8 NADH, and 9 acetyl CoA

Tripalmitin is a TAG formed by the esterification of glycerol with three palmitic acid molecules. How many acetyl CoA molecules will be produced by the complete oxidation of tripalmitin? (Hint: consider glycerol metabolism too).

• A. 22
• B. 24
• C. 25
• D. 26

Here’s what students ask on this topic:

What is the role of acyl CoA synthetase in fatty acid oxidation?

Acyl CoA synthetase plays a crucial role in the activation phase of fatty acid oxidation. This enzyme catalyzes the conversion of fatty acids into fatty acyl CoA, a necessary step for their subsequent metabolism. The reaction requires ATP, which is hydrolyzed to AMP and two inorganic phosphates, effectively consuming the equivalent of two ATP molecules. This activation step is essential because it prepares the fatty acid for transport into the mitochondria, where beta oxidation occurs. Without this activation, fatty acids cannot be efficiently metabolized for energy production.

How does carnitine facilitate the transport of fatty acids into the mitochondria?

Carnitine facilitates the transport of fatty acids into the mitochondria by acting as a shuttle. Fatty acyl CoA cannot directly cross the mitochondrial membrane. Instead, the enzyme carnitine acyl transferase transfers the fatty acyl group from CoA to carnitine, forming fatty acyl carnitine. This molecule can traverse the mitochondrial membrane. Once inside the mitochondrial matrix, the fatty acyl group is transferred back to CoA, forming fatty acyl CoA, which can then enter the beta oxidation pathway. Carnitine is released and can return to the cytosol to repeat the process.

What are the products of one cycle of beta oxidation?

One cycle of beta oxidation produces three main products: one FADH₂, one NADH, and one Acetyl CoA. During this cycle, the fatty acid chain is shortened by two carbon atoms. The FADH₂ and NADH are high-energy molecules that will enter the electron transport chain to produce ATP. The Acetyl CoA can enter the citric acid cycle (Krebs cycle) for further oxidation, leading to additional ATP production. This cyclical process continues until the entire fatty acid chain is converted into Acetyl CoA units.

What is the energy cost associated with fatty acid activation?

The energy cost associated with fatty acid activation is the equivalent of two ATP molecules. During the activation phase, acyl CoA synthetase catalyzes the conversion of a fatty acid to fatty acyl CoA, utilizing ATP. This ATP is hydrolyzed to AMP and two inorganic phosphates, which is energetically equivalent to consuming two ATP molecules. This initial energy investment is crucial for preparing the fatty acid for subsequent transport into the mitochondria and entry into the beta oxidation pathway.

How is the energy output of beta oxidation calculated?

The energy output of beta oxidation depends on the number of carbon atoms in the fatty acid. Each cycle of beta oxidation cleaves two carbons, producing one FADH₂, one NADH, and one Acetyl CoA. The total number of cycles is calculated as (number of carbons/2) - 1. For example, an 8-carbon fatty acid undergoes 3 cycles, producing 3 FADH₂, 3 NADH, and 4 Acetyl CoA. The initial activation of the fatty acid has a one-time cost of 2 ATP. The FADH₂ and NADH enter the electron transport chain, contributing to ATP production.