Understanding the Oxidative Energy System

At this point in the bioenergetics lecture series, we've already covered the ATP-PC system, where phosphocreatine is used to create or synthesize one ATP. The phosphate from that phosphocreatine is split off, and that phosphate is attached to an ADP in its most simplistic form. That's what's happening with the ATP-PC system. The primary Enzyme for that reaction is creatine kinase. Then I covered glycolysis, which is the breakdown of glucose or glycogen. And that is about a 12-step cascade of chemical reactions. The rate-limiting enzyme for glycolysis is phosphofructokinase. We can abbreviate that PFK. And then the final product of glycolysis, in addition to the A... ATPs and the NADHs that are produced during that series of chemical reactions, we end up with two pyruvates. And I mentioned also in that lecture that those two pyruvates can have two different fates. And what their fate is, is dependent upon the presence of oxygen. If there's no oxygen present or oxygen is insufficient or is not being supplied quickly enough, those pyruvates will be converted into lactate. or lactic acid, which dissociates into lactate and a hydrogen. If oxygen is present, those pyruvates, they have to be converted into something first and we're going to get into that. But if oxygen's present, we can use those pyruvates to make ATP in this oxidative system, which is what our primary focus will be for this lecture. So just looking at the name of this energy system, it's the oxidative system. This implies that oxygen is required. So this is an aerobic energy system, which is different from the previous two. The previous two can occur under anaerobic conditions. So the oxidative system should be obvious from the name. It's aerobic, so we have to have oxygen. ATP yield is also a major difference between this energy system and the others. You can mass produce, our bodies mass produce ATP. using this oxidative system. So with one glucose, we can generate 32 to 33 ATP. And that depends on if you're starting with glucose or glycogen. And we'll also talk about this during this lecture. If you start from one, you break down a triglyceride or a lipid of fat into a free fatty acid. One free fatty acid, after it goes through the series of reactions through the oxidative system, can generate... over a hundred ATP and there are different sizes of free fatty acids. Some of them are much larger compounds than others. And so that's why we've got, uh, we don't have a definitive number. It varies based on the type of free fatty acid that's being metabolized. So a hundred or more, and that is drastically more than ATP, ATP PC system, which can yield one for every one phosphocreatine. Um, and then glycolysis. the anaerobic glycolysis that we've discussed where you get either two or three ATP. Now we're up to 32 to 33 or over a hundred. So a lot of energy can be created using this oxidative system. In the other energy systems, ATP PC system, we discussed it will run for, it'll be the primary energy system for events or activities lasting between three. 15 seconds. After that 15 seconds, phosphocretine has been depleted. So that's when glycolysis will take over and it can run its duration is 15 seconds to 2 minutes. After 2 minutes, we're going to be primarily relying on this oxidative system. And so the duration that we've defined in this for this energy system is 2 minutes to infinity. And infinity may not be factually correct. Um, but I think I've mentioned in a previous lecture that, uh, our, our, the fat we have stored in our body is, is very energy dense. Uh, so energy dense, we have so much energy stored in our fat adipose tissue, and we're not going to burn through that in any single bout of exercise. It would take many, many bouts and, uh, you know, not eating. And I mean, it would be, you would have to, you know, you'd have to be in a really tough situation in order for you to actually burn all of your body fat. And so that's why we have infinity here. For as long as you can run, you're probably going to be. relying on this oxidative energy system. So looking at this timeframe, two minutes to infinity, the oxidative system is really critical for distance events or longer duration, lower intensity exercise bouts. And so one thing with this energy system is it has a very large ATP yield. So it yields a lot of ATP. The downside to it is it's much slower compared to the ATP PC system and glycolysis, which is why that duration is two minutes to infinity. So it produces a lot, but it takes a while for this energy system to really get started up and to start producing ATP. So it's the slowest of the three energy systems, but also yields the most ATP. It's also the most complex. There are two major... kind of divisions of this oxidative system that we'll talk about. And another difference between the oxidative system and the other two energy systems is that these reactions occur in the mitochondria of the cell, not in the cytoplasm like the previous two. And if you recall ever hearing probably in maybe elementary, middle, maybe even high school, the powerhouse of the cell is often what the mitochondria is referred to as. And that's not where all ATP and energy is made, but that's where a lot of it is made. And the reason it was called that or referred to as the powerhouse of the cell is because of the large amount of ATP that can be produced in the mitochondria via this oxidative energy system. So I'll give you a quick overview before I dive into this what we're going to do in this lecture. is first look at the oxidation of carbohydrates. Then we will look at the oxidation of fats. And then we will look at briefly the oxidation of proteins, how we use protein. That will be very limited. And then we will also get into the interaction between these energy systems. So starting off with oxidation of carbohydrates, the first step is glycolysis, which you should be pretty familiar with at this point. It was discussed in the last video. So we're starting with carbohydrates or glucose glycogen. It goes through glycolysis and then at the end of glycolysis we have pyruvate. If oxygen is present that pyruvate will then be converted into something we'll call acetyl-CoA and then it can enter the Krebs cycle. And then all of the hydrogens, if you remember the NADs that pick up the hydrogens, they're the hydrogen shuttles, will have a couple different hydrogen shuttles. NAD and FAD that are going to transport all of those hydrogens to the electron transport chain. So the Krebs cycle and the electron transport chain are really the two sort of divisions of this oxidative system. So here is where I'll just give you an overview of the metabolism, complete oxidative metabolism of glucose, or in this case glucose, but it's glucose or glycogen. Because what we have in this top image here, this top box labeled A, we start with glucose. It undergoes several chemical reactions. We have to invest two ATP in that energy input phase. Our output is two NADHs and four ATP with a net of two ATP here. And at the end, we end up with two pyruvates. So hopefully you've identified this block. this A figure, this is glycolysis, just as you've learned it in the last lecture. So we end up with these two pyruvates. Now, if oxygen is present, this pyruvate will continue down into the mitochondria. Pyruvate will be converted into acetyl-CoA. Only acetyl-CoA can enter the Krebs cycle, which is the next step. So this conversion is critical. During this conversion, pyruvate to acetyl CoA, NADHs are produced in this kind of preliminary step to the Krebs cycle. So during this conversion we do produce two more NADHs and these are going to be important later. Those two acetyl CoAs then they each complete one turn of the Krebs cycle. So what we're looking at here is the sum of both of those turns. So two turns these are going to be our products. six total NADHs, two FADHs, and I'll explain what that is in just a second. We'll get two substrate level phosphorylation ATPs. So these two ATPs are directly made during the Krebs cycle. And then we also end up with water and CO2. And then big picture here, we've talked about the NADs and they pick up these hydrogens that are acidic. They increase the acidity and if they accumulate, that's detrimental to exercise and performance. The NADs are hydrogen transporters. This FAD down here is, it has the exact same function. The FADs are going to be picking up these hydrogens and transporting them to the electron transport chain. And that is what you can see in this image. These hydrogens here, the hydrogens from these NADHs, FADHs, all of those shuttle molecules are taking these hydrogens to the electron transport chain. And we'll get into that. little bit today and those electrons are going to be passed down several cytochromes and used to make ATP. So this is the overall gist. We start with glycolysis. If oxygen is present we go pyruvate to acetyl CoA. We have production of two NADHs and then those two acetyl CoAs, only acetyl CoA can enter the Krebs cycle. So those two acetyl CoAs enter the Krebs cycle with a product of six NADHs, two FADHs, two ATP, water, and CO2. All of the hydrogens produced both in glycolysis and the Krebs cycle are going to be transported to the electron transport chain. So I've already discussed all this, but we're going to kind of recap. Some of this, if you recall from glycolysis, we're going to revisit glycolysis briefly. Glycolysis can occur with or without oxygen. It can occur regardless of whether we are in an anaerobic environment or not. When O2 is present, we will proceed from glycolysis into the Krebs cycle, which is what we were looking at in that image on the previous slide. This is the end of glycolysis here where my mouse is. When oxygen is present, we will proceed into the Krebs cycle. This is the preliminary step. This has to occur in order for us to enter the Krebs cycle, and that is that pyruvate must be converted into acetyl-CoA, which is this step here. Okay, only acetyl-CoA can enter the Krebs cycle. Only acetyl-CoA. So for the Krebs cycle, just like with all of the other energy systems, there is a rate limiting enzyme that limits the rate or the speed of this reaction or these reactions rather. So for the Krebs cycle, the rate limiting enzyme is isocitrate dehydrogenase. So for in the Krebs cycle, just within the Krebs cycle, we're starting with glycolysis. With glucose, because we're focused on the oxidation of carbohydrates, we start with glucose. Ultimately, that is converted into two pyruvic acids or two pyruvates. From there, those two pyruvates are converted into two acetyl-CoAs. And we have two complete turns of the Krebs cycle, one for each of those acetyl-CoAs. So we have double ATP yield. And all of this stems, if you remember from glycolysis, there were three phases. We had the energy input. Molecular division phase was the second one where we had a six carbon sugar. It was split into two, three carbons. So everything is duplicated from that point forward. That's why we end up with two pyruvates, two acetyl-CoAs, and two turns of the Krebs cycle. So double the ATP yield because of that molecular division phase in glycolysis. So here's a list of the products of the Krebs cycle. So it produces GTP or ATP. So this is substrate level phosphorylation. What we're going to do in this class for simplification is we're just going to treat this as an ATP. You'll see GTP, but just know that that is used to create an ATP very quickly. So we're just going to refer to it as an ATP. NADH is also produced and you should be familiar with that. The NADs are hydrogen transporters. We've got FADH being produced, which serves the same purpose. It's a hydrogen shuttle. And we also have these hydrogens produced. And just like with glycolysis, the accumulation of these hydrogens creates a very acidic environment. And there are a lot of negative consequences in terms of muscle contraction and metabolism that are associated with the accumulation of these hydrogens. So not good. Not good if we have a lot of hydrogens. circulating inside of the mitochondria or in the cytoplasm of the cell. So we deal with those hydrogens by transporting them to the electron transport chain via NAD and FAD. So here are the quantity of products for one turn of the Krebs cycle. So this is when we input one acetyl-CoA into the Krebs cycle. At the end of glycolysis, we have two pyruvates. So we really have two acetyl-CoAs, but this is, I just want to make sure that you understand this is one turn of the Krebs cycle. So input of one acetyl-CoA. So for every full turn, we produce three NADHs, one FADH, one ATP, and then two carbon dioxides. So ultimately I've got in yellow here, remember that The Krebs cycle, there are two turns when we are metabolizing glucose or glycogen, two turns of the Krebs cycle. So this is actually going to be six NADHs, two FADHs, two ATP, and four CO2s. So here's a little more in-depth look at the Krebs cycle. Specifically, we have... We're starting with one pyruvate here, even though two are produced. So we're looking at one turn processing one pyruvate or one acetyl-CoA. So the pyruvate is converted to acetyl-CoA during this conversion. So this is like a between glycolysis and the Krebs cycle step. And it's also important to remember here, and it's easy to forget, that we have an NADH produced during this preliminary step. It's actually one NADH for each pyruvate. So pyruvate is converted into acetyl-CoA because only acetyl-CoA can enter the Krebs cycle. And then you can follow the cycle around. And what you're going to see are these products, what acetyl-CoA is being broken down into, and then the enzymes that are associated with that step in the Krebs cycle. Now, the only enzyme that I would like for you to remember is the rate-limiting enzyme. for the Krebs cycle, which is right here, isocitrate dehydrogenase. You'll need to know that rate limiting enzyme. And the others I don't want you to be too concerned with, but I just did want to show you what the full Krebs cycle looks like. And so as we continue down this Krebs cycle, you can see where each of these NADHs and FADHs and ATP are being produced. So we've got an NADH right off the bat with a CO2. Another NADH here, another CO2 here, the ATP or GTP, we're going to refer to it as just ATP or produced down here. And then we have FADH here. And then finally, our last NADH. So this is just where they're all produced within that cycle, if you were curious about that. Another note here with the CO2, I'm not. I care more that you understand the other products, the NADH, the FADH, and the ATP. The CO2, I'm not too concerned with right now for the purposes of this class, but there's one thing I want to point out. You know that when you exercise, or even when you're just sitting here, we're using energy. We have metabolism occurring, so we're making ATP even just sitting here, but especially during exercise, we're... making much more ATP much more rapidly. And when we start to exercise, we're blowing off a lot more CO2. Even as we're sitting here, we're blowing off CO2. But a lot of that CO2, this is where it's being generated. CO2 is a byproduct of ATP production. And so that's really all I wanted to point out in terms of the CO2 here. I really want you to know the NADHs, FADHs, and the ATP. So at this point, You can find this worksheet on Blackboard under note pages. Enzyme chain up here, this is the Krebs cycle or you can call this oxidative phosphorylation. So I'll go ahead and give you that one. Oxidative phosphorylation here at the top and then of course we're starting with pyruvate. I'd like for you to just use one pyruvate here. Okay so we're gonna do one turn. of the Krebs cycle for one pyruvate. And just make a note that this happens twice. Just like with the previous worksheet, this green line over here should probably be an arrow. There's something or some things being transported out of this Krebs cycle, away from this cycle. So here I'd like for you to put whatever those are that are being transported, where they're headed. what's their destination? So you can pause the video, try to complete this the best you can, and I will show you the answers here in just a minute. So here are, here's a completed worksheet. We've got oxidative phosphorylation at the top. We start with pyruvate. The first thing, this is that preliminary step. The first thing that has to happen is we have to convert this pyruvate to acetyl-CoA because only acetyl-CoA can enter the Krebs cycle. During this step, we are producing one NADH, also a CO2. I want you to be more concerned with the NADH. And it also, it doesn't matter which side you put these on, as long as you know this is where this NADH is produced. So we have an NADH produced here, NADH here, as well as here, an ATP at the bottom, one total FADH for one turn of the Krebs cycle, and a third NADH here. That's actually a fourth if we count this one in the preliminary step. For this line, each of these NADHs and FADHs, those are going to be traveling to the electron transport chain to drop off these hydrogens. They will then come back to the Krebs cycle to pick up more hydrogens. So they're just constantly shuttling those hydrogens. Now let's get into the electron transport chain. And so the electron transport chain, again, is where all of these hydrogens are being transported to. And we're actually going to use those hydrogens and the electrons on those hydrogens to create more ATP. Actually, this is where the most ATP is going to be created within this oxidative system. So again, we have another kind of part of the system here and it has its own rate limiting enzyme. The rate limiting enzyme for the electron transport chain is cytochrome oxidase. Now oxidase is... It should be fairly easy to remember because oxygen is critical here. It's the final electron acceptor for the electron transport chain. So this is an oxidative process. So maybe that will help you remember. And then the cytochrome, I'm going to show you an image, an illustration, and we're going to be looking at the inner membrane of the mitochondria. And there will be in the image, they're purple, these structures, these cytochromes, which are going to basically do the work. during this electron transport chain. This is they're going to be basically pumps for these hydrogens and these electrons. So those are called cytochromes. So we have cytochrome oxidase is the rate limiting enzyme for the electron transport chain. So here's a question for you. The hydrogens we've got these electrons that are carried to the electron transport chain. What is carrying those hydrogens? You should have NAD and FAD. your answers. NAD and FAD are the transporters. And so these hydrogens and electrons are traveling down this electron transport chain. And you'll see that in the next image. The hydrogens are ultimately going to combine with oxygen. It's the final acceptor in this process and ultimately forms H2O water. And so the electrons plus the oxygen do help form ATP. This is a critical piece of information for you all. We've really hammered, you know, we've talked about NADH and FADH quite a lot. And this is when they start to really get important because we're going to calculate how much ATB is being produced for each of those. So for every NADH that travels to the electron transport chain and passes off those electrons, that hydrogen, two and a half ATP will be created from that one NADH. Okay, for every single FADH, and so for every one turn of the Krebs cycle, we produce one FADH. That's the only source of FADH within the oxidative system. So we ultimately have two because we always have two turns of the Krebs cycle. For every one FADH, we get 1.5 ATP. Okay, so two and a half per NADH, one and a half ATP per FADH. So here is the electron transport chain. If you look up here in the top left somewhat corner, we've got the mitochondria here and inside this black box is where we are zoomed in. So what we're looking at is the matrix. So the very inside of the mitochondria here, then we have the inner mitochondrial membrane, and then there's this kind of gap. If you can see it in this image between the inner mitochondrial membrane and the outer membrane, and that is the area, the space between those is this outer mitochondrial compartment. And so these hydrogens and these electrons are being pumped across this inner mitochondrial membrane through these cytochromes. Keep in mind the cytochromes, that's why. the rate limiting enzyme is called cytochrome oxidase. So each of these purple structures here are your cytochromes. So what this is really illustrating here is that we just have these NADHs and FADHs via different cytochromes. These cytochromes, some of them are specific, but they're essentially dropping off these hydrogens and pumping these electrons down this chain of cytochromes. and you can follow the path of each of these electrons that are being stripped, as well as the hydrogens that are being pumped. Now, without going into too much detail and making this too complex, we have a series of hydrogens being pumped through the cytochromes. The electrons that are stripped from those are being passed from cytochrome to cytochrome. Ultimately, we end up down here on the right side. We have these hydrogens being pumped back into the matrix. You see here ATP synthase. This has the ace suffix, ace ending. So we know that's an enzyme, ATP synthase. Synthase sounds like synthesizing. So this is an enzyme that's responsible for synthesizing ATP at the end, the terminal end of this electron transport chain. And so that's what we have here. the energy from these electrons and from pumping these hydrogens back through into the matrix ultimately generate ATP. Now how much ATP? Two and a half for every NADH that arrives at the electron transport chain and one and a half ATP for every FADH that arrives at the electron transport chain. So here's where the quantity of ATP being produced starts to add up. What we're going to do here before you even look at this, what we're going to do here is actually count the total number of ATP being produced from the complete metabolism of, in this case, glucose. We're starting with glucose. So this is complete oxidative metabolism of glucose. Before we start, do you remember how much ATP we receive from the anaerobic metabolism of glucose when oxygen is not present. That's when we just go through glycolysis and at the end we're left with pyruvate converted to lactate. We really only get two ATP from glucose, three from glycogen at that point. But when oxygen is present, we have the complete oxidative metabolism of glucose. And so we produce a lot more because those pyruvates at the end can enter the Krebs cycle and be processed aerobically to make ATP. So from the top here, we're including glycolysis in this because that is the first step within the oxidative metabolism of a carbohydrate. So we start with glucose, the investment period there, or what I call phase one, the input phase where you have to invest and then wait for your larger return later on. You have to invest to ATP when you start with glucose right out of the gate. You invest to the output there. is four ATP, so we end up with a net of two. And that's what we see here at the top. All right, we used two ATP, we got four out, but the net there is only two. So this is substrate level phosphorylation. These ATP are being directly made from this reaction. So we make two ATP here. Also, we have two NADHs formed during glycolysis. Remember, for every one NADH, we get two and a half ATP. So with two NADHs here, those travel to the electron transport chain and drop off those hydrogens. So at two NADHs at two and a half a piece, we end up with five ATP. Ultimately, we end up with pyruvate. And again, this is an oxidative process. So those pyruvates are converted into acetyl-CoA during that step. That kind of... step in between glycolysis and the Krebs cycle, two NADHs are produced, one for each pyruvate. So we got two more NADHs here and at two and a half ATP per, that gives us another five ATP. So now we're entering the Krebs cycle because only acetyl-CoA can enter the Krebs cycle. So what we have here and for the rest of this image down here in the bottom, this is the total. So this is for... both spins for two spins of the Krebs cycle. So our totals are six and ADHs at two and a half ATP per. We get 15 ATP. We produce one FADH for every turn of the Krebs cycle. So we end up with two and at one and a half ATP per FADH, we end up with three ATP from those sources. And then we also, you remember the GTP to ATP, we're just going to count them as ATP, that's substrate level phosphorylation, and we get one for each turn. So we end up with two more ATP down there at the bottom. So the total energy yield from the complete oxidative metabolism of a glucose is 32 ATP. One thing I want to point out here is all of this inside of this green box, These are all your NADHs and FADHs. And so these are clumped together here just to illustrate that all of these, all of this ATP is being processed, is being synthesized in the electron transport chain. And so outside of this box you see that we get two here and two here. That's only four of the 32 ATP that are not coming from the electron transport chain. Most of the ATP we're getting from this oxidative system is actually coming from the processes that happen within this electron transport chain. So here's a different way to look at the breakdown of net totals. It doesn't really illustrate where all these are coming from. It's just kind of the big picture. So we've got a breakdown of our net totals for ATP for the, again, look at the top, oxidation of carbohydrate. So aerobic process. So from glycolysis, we get either two or three ATP. We get two if we start with glucose. We get three if we start with glycogen. We get the ATP from substrate level phosphorylation from the Krebs cycle. So we get two ATP, one from each turn. We have a cumulative total of 10 NADHs. So 10 times two and a half because we get two and a half ATP for every one NADH gives us 25 ATP. From our two FADHs at one and a half ATP each, we get three ATP. So the net totals for glucose, 32 ATP, glycogen 33, just because of that difference in the energy input phase in glycolysis.

The primary Enzyme for that reaction is creatine kinase. Then I covered glycolysis, which is the breakdown of glucose or glycogen. And that is about a 12-step cascade of chemical reactions. The rate-limiting enzyme for glycolysis is phosphofructokinase. We can abbreviate that PFK.

And then the final product of glycolysis, in addition to the A... ATPs and the NADHs that are produced during that series of chemical reactions, we end up with two pyruvates. And I mentioned also in that lecture that those two pyruvates can have two different fates. And what their fate is, is dependent upon the presence of oxygen.

If there's no oxygen present or oxygen is insufficient or is not being supplied quickly enough, those pyruvates will be converted into lactate. or lactic acid, which dissociates into lactate and a hydrogen. If oxygen is present, those pyruvates, they have to be converted into something first and we're going to get into that.

But if oxygen's present, we can use those pyruvates to make ATP in this oxidative system, which is what our primary focus will be for this lecture. So just looking at the name of this energy system, it's the oxidative system. This implies that oxygen is required. So this is an aerobic energy system, which is different from the previous two.

The previous two can occur under anaerobic conditions. So the oxidative system should be obvious from the name. It's aerobic, so we have to have oxygen. ATP yield is also a major difference between this energy system and the others.

You can mass produce, our bodies mass produce ATP. using this oxidative system. So with one glucose, we can generate 32 to 33 ATP. And that depends on if you're starting with glucose or glycogen. And we'll also talk about this during this lecture.

If you start from one, you break down a triglyceride or a lipid of fat into a free fatty acid. One free fatty acid, after it goes through the series of reactions through the oxidative system, can generate... over a hundred ATP and there are different sizes of free fatty acids.

Some of them are much larger compounds than others. And so that's why we've got, uh, we don't have a definitive number. It varies based on the type of free fatty acid that's being metabolized. So a hundred or more, and that is drastically more than ATP, ATP PC system, which can yield one for every one phosphocreatine. Um, and then glycolysis.

the anaerobic glycolysis that we've discussed where you get either two or three ATP. Now we're up to 32 to 33 or over a hundred. So a lot of energy can be created using this oxidative system.

In the other energy systems, ATP PC system, we discussed it will run for, it'll be the primary energy system for events or activities lasting between three. 15 seconds. After that 15 seconds, phosphocretine has been depleted.

So that's when glycolysis will take over and it can run its duration is 15 seconds to 2 minutes. After 2 minutes, we're going to be primarily relying on this oxidative system. And so the duration that we've defined in this for this energy system is 2 minutes to infinity.

And infinity may not be factually correct. Um, but I think I've mentioned in a previous lecture that, uh, our, our, the fat we have stored in our body is, is very energy dense. Uh, so energy dense, we have so much energy stored in our fat adipose tissue, and we're not going to burn through that in any single bout of exercise. It would take many, many bouts and, uh, you know, not eating.

And I mean, it would be, you would have to, you know, you'd have to be in a really tough situation in order for you to actually burn all of your body fat. And so that's why we have infinity here. For as long as you can run, you're probably going to be.

relying on this oxidative energy system. So looking at this timeframe, two minutes to infinity, the oxidative system is really critical for distance events or longer duration, lower intensity exercise bouts. And so one thing with this energy system is it has a very large ATP yield. So it yields a lot of ATP.

The downside to it is it's much slower compared to the ATP PC system and glycolysis, which is why that duration is two minutes to infinity. So it produces a lot, but it takes a while for this energy system to really get started up and to start producing ATP. So it's the slowest of the three energy systems, but also yields the most ATP.

It's also the most complex. There are two major... kind of divisions of this oxidative system that we'll talk about.

And another difference between the oxidative system and the other two energy systems is that these reactions occur in the mitochondria of the cell, not in the cytoplasm like the previous two. And if you recall ever hearing probably in maybe elementary, middle, maybe even high school, the powerhouse of the cell is often what the mitochondria is referred to as. And that's not where all ATP and energy is made, but that's where a lot of it is made. And the reason it was called that or referred to as the powerhouse of the cell is because of the large amount of ATP that can be produced in the mitochondria via this oxidative energy system.

So I'll give you a quick overview before I dive into this what we're going to do in this lecture. is first look at the oxidation of carbohydrates. Then we will look at the oxidation of fats. And then we will look at briefly the oxidation of proteins, how we use protein. That will be very limited.

And then we will also get into the interaction between these energy systems. So starting off with oxidation of carbohydrates, the first step is glycolysis, which you should be pretty familiar with at this point. It was discussed in the last video. So we're starting with carbohydrates or glucose glycogen. It goes through glycolysis and then at the end of glycolysis we have pyruvate.

If oxygen is present that pyruvate will then be converted into something we'll call acetyl-CoA and then it can enter the Krebs cycle. And then all of the hydrogens, if you remember the NADs that pick up the hydrogens, they're the hydrogen shuttles, will have a couple different hydrogen shuttles. NAD and FAD that are going to transport all of those hydrogens to the electron transport chain. So the Krebs cycle and the electron transport chain are really the two sort of divisions of this oxidative system.

So here is where I'll just give you an overview of the metabolism, complete oxidative metabolism of glucose, or in this case glucose, but it's glucose or glycogen. Because what we have in this top image here, this top box labeled A, we start with glucose. It undergoes several chemical reactions.

We have to invest two ATP in that energy input phase. Our output is two NADHs and four ATP with a net of two ATP here. And at the end, we end up with two pyruvates. So hopefully you've identified this block. this A figure, this is glycolysis, just as you've learned it in the last lecture.

So we end up with these two pyruvates. Now, if oxygen is present, this pyruvate will continue down into the mitochondria. Pyruvate will be converted into acetyl-CoA.

Only acetyl-CoA can enter the Krebs cycle, which is the next step. So this conversion is critical. During this conversion, pyruvate to acetyl CoA, NADHs are produced in this kind of preliminary step to the Krebs cycle.

So during this conversion we do produce two more NADHs and these are going to be important later. Those two acetyl CoAs then they each complete one turn of the Krebs cycle. So what we're looking at here is the sum of both of those turns. So two turns these are going to be our products.

six total NADHs, two FADHs, and I'll explain what that is in just a second. We'll get two substrate level phosphorylation ATPs. So these two ATPs are directly made during the Krebs cycle.

And then we also end up with water and CO2. And then big picture here, we've talked about the NADs and they pick up these hydrogens that are acidic. They increase the acidity and if they accumulate, that's detrimental to exercise and performance.

The NADs are hydrogen transporters. This FAD down here is, it has the exact same function. The FADs are going to be picking up these hydrogens and transporting them to the electron transport chain. And that is what you can see in this image.

These hydrogens here, the hydrogens from these NADHs, FADHs, all of those shuttle molecules are taking these hydrogens to the electron transport chain. And we'll get into that. little bit today and those electrons are going to be passed down several cytochromes and used to make ATP. So this is the overall gist.

We start with glycolysis. If oxygen is present we go pyruvate to acetyl CoA. We have production of two NADHs and then those two acetyl CoAs, only acetyl CoA can enter the Krebs cycle.

So those two acetyl CoAs enter the Krebs cycle with a product of six NADHs, two FADHs, two ATP, water, and CO2. All of the hydrogens produced both in glycolysis and the Krebs cycle are going to be transported to the electron transport chain. So I've already discussed all this, but we're going to kind of recap. Some of this, if you recall from glycolysis, we're going to revisit glycolysis briefly.

Glycolysis can occur with or without oxygen. It can occur regardless of whether we are in an anaerobic environment or not. When O2 is present, we will proceed from glycolysis into the Krebs cycle, which is what we were looking at in that image on the previous slide.

This is the end of glycolysis here where my mouse is. When oxygen is present, we will proceed into the Krebs cycle. This is the preliminary step.

This has to occur in order for us to enter the Krebs cycle, and that is that pyruvate must be converted into acetyl-CoA, which is this step here. Okay, only acetyl-CoA can enter the Krebs cycle. Only acetyl-CoA.

So for the Krebs cycle, just like with all of the other energy systems, there is a rate limiting enzyme that limits the rate or the speed of this reaction or these reactions rather. So for the Krebs cycle, the rate limiting enzyme is isocitrate dehydrogenase. So for in the Krebs cycle, just within the Krebs cycle, we're starting with glycolysis. With glucose, because we're focused on the oxidation of carbohydrates, we start with glucose.

Ultimately, that is converted into two pyruvic acids or two pyruvates. From there, those two pyruvates are converted into two acetyl-CoAs. And we have two complete turns of the Krebs cycle, one for each of those acetyl-CoAs.

So we have double ATP yield. And all of this stems, if you remember from glycolysis, there were three phases. We had the energy input.

Molecular division phase was the second one where we had a six carbon sugar. It was split into two, three carbons. So everything is duplicated from that point forward.

That's why we end up with two pyruvates, two acetyl-CoAs, and two turns of the Krebs cycle. So double the ATP yield because of that molecular division phase in glycolysis. So here's a list of the products of the Krebs cycle. So it produces GTP or ATP.

So this is substrate level phosphorylation. What we're going to do in this class for simplification is we're just going to treat this as an ATP. You'll see GTP, but just know that that is used to create an ATP very quickly. So we're just going to refer to it as an ATP. NADH is also produced and you should be familiar with that.

The NADs are hydrogen transporters. We've got FADH being produced, which serves the same purpose. It's a hydrogen shuttle. And we also have these hydrogens produced. And just like with glycolysis, the accumulation of these hydrogens creates a very acidic environment.

And there are a lot of negative consequences in terms of muscle contraction and metabolism that are associated with the accumulation of these hydrogens. So not good. Not good if we have a lot of hydrogens. circulating inside of the mitochondria or in the cytoplasm of the cell. So we deal with those hydrogens by transporting them to the electron transport chain via NAD and FAD.

So here are the quantity of products for one turn of the Krebs cycle. So this is when we input one acetyl-CoA into the Krebs cycle. At the end of glycolysis, we have two pyruvates. So we really have two acetyl-CoAs, but this is, I just want to make sure that you understand this is one turn of the Krebs cycle. So input of one acetyl-CoA.

So for every full turn, we produce three NADHs, one FADH, one ATP, and then two carbon dioxides. So ultimately I've got in yellow here, remember that The Krebs cycle, there are two turns when we are metabolizing glucose or glycogen, two turns of the Krebs cycle. So this is actually going to be six NADHs, two FADHs, two ATP, and four CO2s.

So here's a little more in-depth look at the Krebs cycle. Specifically, we have... We're starting with one pyruvate here, even though two are produced.

So we're looking at one turn processing one pyruvate or one acetyl-CoA. So the pyruvate is converted to acetyl-CoA during this conversion. So this is like a between glycolysis and the Krebs cycle step. And it's also important to remember here, and it's easy to forget, that we have an NADH produced during this preliminary step.

It's actually one NADH for each pyruvate. So pyruvate is converted into acetyl-CoA because only acetyl-CoA can enter the Krebs cycle. And then you can follow the cycle around. And what you're going to see are these products, what acetyl-CoA is being broken down into, and then the enzymes that are associated with that step in the Krebs cycle.

Now, the only enzyme that I would like for you to remember is the rate-limiting enzyme. for the Krebs cycle, which is right here, isocitrate dehydrogenase. You'll need to know that rate limiting enzyme. And the others I don't want you to be too concerned with, but I just did want to show you what the full Krebs cycle looks like. And so as we continue down this Krebs cycle, you can see where each of these NADHs and FADHs and ATP are being produced.

So we've got an NADH right off the bat with a CO2. Another NADH here, another CO2 here, the ATP or GTP, we're going to refer to it as just ATP or produced down here. And then we have FADH here. And then finally, our last NADH.

So this is just where they're all produced within that cycle, if you were curious about that. Another note here with the CO2, I'm not. I care more that you understand the other products, the NADH, the FADH, and the ATP. The CO2, I'm not too concerned with right now for the purposes of this class, but there's one thing I want to point out. You know that when you exercise, or even when you're just sitting here, we're using energy.

We have metabolism occurring, so we're making ATP even just sitting here, but especially during exercise, we're... making much more ATP much more rapidly. And when we start to exercise, we're blowing off a lot more CO2. Even as we're sitting here, we're blowing off CO2. But a lot of that CO2, this is where it's being generated.

CO2 is a byproduct of ATP production. And so that's really all I wanted to point out in terms of the CO2 here. I really want you to know the NADHs, FADHs, and the ATP. So at this point, You can find this worksheet on Blackboard under note pages. Enzyme chain up here, this is the Krebs cycle or you can call this oxidative phosphorylation.

So I'll go ahead and give you that one. Oxidative phosphorylation here at the top and then of course we're starting with pyruvate. I'd like for you to just use one pyruvate here.

Okay so we're gonna do one turn. of the Krebs cycle for one pyruvate. And just make a note that this happens twice. Just like with the previous worksheet, this green line over here should probably be an arrow. There's something or some things being transported out of this Krebs cycle, away from this cycle.

So here I'd like for you to put whatever those are that are being transported, where they're headed. what's their destination? So you can pause the video, try to complete this the best you can, and I will show you the answers here in just a minute.

So here are, here's a completed worksheet. We've got oxidative phosphorylation at the top. We start with pyruvate.

The first thing, this is that preliminary step. The first thing that has to happen is we have to convert this pyruvate to acetyl-CoA because only acetyl-CoA can enter the Krebs cycle. During this step, we are producing one NADH, also a CO2. I want you to be more concerned with the NADH. And it also, it doesn't matter which side you put these on, as long as you know this is where this NADH is produced.

So we have an NADH produced here, NADH here, as well as here, an ATP at the bottom, one total FADH for one turn of the Krebs cycle, and a third NADH here. That's actually a fourth if we count this one in the preliminary step. For this line, each of these NADHs and FADHs, those are going to be traveling to the electron transport chain to drop off these hydrogens.

They will then come back to the Krebs cycle to pick up more hydrogens. So they're just constantly shuttling those hydrogens. Now let's get into the electron transport chain.

And so the electron transport chain, again, is where all of these hydrogens are being transported to. And we're actually going to use those hydrogens and the electrons on those hydrogens to create more ATP. Actually, this is where the most ATP is going to be created within this oxidative system. So again, we have another kind of part of the system here and it has its own rate limiting enzyme. The rate limiting enzyme for the electron transport chain is cytochrome oxidase.

Now oxidase is... It should be fairly easy to remember because oxygen is critical here. It's the final electron acceptor for the electron transport chain.

So this is an oxidative process. So maybe that will help you remember. And then the cytochrome, I'm going to show you an image, an illustration, and we're going to be looking at the inner membrane of the mitochondria.

And there will be in the image, they're purple, these structures, these cytochromes, which are going to basically do the work. during this electron transport chain. This is they're going to be basically pumps for these hydrogens and these electrons.

So those are called cytochromes. So we have cytochrome oxidase is the rate limiting enzyme for the electron transport chain. So here's a question for you. The hydrogens we've got these electrons that are carried to the electron transport chain. What is carrying those hydrogens?

You should have NAD and FAD. your answers. NAD and FAD are the transporters.

And so these hydrogens and electrons are traveling down this electron transport chain. And you'll see that in the next image. The hydrogens are ultimately going to combine with oxygen. It's the final acceptor in this process and ultimately forms H2O water.

And so the electrons plus the oxygen do help form ATP. This is a critical piece of information for you all. We've really hammered, you know, we've talked about NADH and FADH quite a lot.

And this is when they start to really get important because we're going to calculate how much ATB is being produced for each of those. So for every NADH that travels to the electron transport chain and passes off those electrons, that hydrogen, two and a half ATP will be created from that one NADH. Okay, for every single FADH, and so for every one turn of the Krebs cycle, we produce one FADH. That's the only source of FADH within the oxidative system.

So we ultimately have two because we always have two turns of the Krebs cycle. For every one FADH, we get 1.5 ATP. Okay, so two and a half per NADH, one and a half ATP per FADH. So here is the electron transport chain. If you look up here in the top left somewhat corner, we've got the mitochondria here and inside this black box is where we are zoomed in.

So what we're looking at is the matrix. So the very inside of the mitochondria here, then we have the inner mitochondrial membrane, and then there's this kind of gap. If you can see it in this image between the inner mitochondrial membrane and the outer membrane, and that is the area, the space between those is this outer mitochondrial compartment. And so these hydrogens and these electrons are being pumped across this inner mitochondrial membrane through these cytochromes.

Keep in mind the cytochromes, that's why. the rate limiting enzyme is called cytochrome oxidase. So each of these purple structures here are your cytochromes. So what this is really illustrating here is that we just have these NADHs and FADHs via different cytochromes.

These cytochromes, some of them are specific, but they're essentially dropping off these hydrogens and pumping these electrons down this chain of cytochromes. and you can follow the path of each of these electrons that are being stripped, as well as the hydrogens that are being pumped. Now, without going into too much detail and making this too complex, we have a series of hydrogens being pumped through the cytochromes.

The electrons that are stripped from those are being passed from cytochrome to cytochrome. Ultimately, we end up down here on the right side. We have these hydrogens being pumped back into the matrix. You see here ATP synthase. This has the ace suffix, ace ending.

So we know that's an enzyme, ATP synthase. Synthase sounds like synthesizing. So this is an enzyme that's responsible for synthesizing ATP at the end, the terminal end of this electron transport chain.

And so that's what we have here. the energy from these electrons and from pumping these hydrogens back through into the matrix ultimately generate ATP. Now how much ATP?

Two and a half for every NADH that arrives at the electron transport chain and one and a half ATP for every FADH that arrives at the electron transport chain. So here's where the quantity of ATP being produced starts to add up. What we're going to do here before you even look at this, what we're going to do here is actually count the total number of ATP being produced from the complete metabolism of, in this case, glucose.

We're starting with glucose. So this is complete oxidative metabolism of glucose. Before we start, do you remember how much ATP we receive from the anaerobic metabolism of glucose when oxygen is not present.

That's when we just go through glycolysis and at the end we're left with pyruvate converted to lactate. We really only get two ATP from glucose, three from glycogen at that point. But when oxygen is present, we have the complete oxidative metabolism of glucose.

And so we produce a lot more because those pyruvates at the end can enter the Krebs cycle and be processed aerobically to make ATP. So from the top here, we're including glycolysis in this because that is the first step within the oxidative metabolism of a carbohydrate. So we start with glucose, the investment period there, or what I call phase one, the input phase where you have to invest and then wait for your larger return later on.

You have to invest to ATP when you start with glucose right out of the gate. You invest to the output there. is four ATP, so we end up with a net of two.

And that's what we see here at the top. All right, we used two ATP, we got four out, but the net there is only two. So this is substrate level phosphorylation.

These ATP are being directly made from this reaction. So we make two ATP here. Also, we have two NADHs formed during glycolysis.

Remember, for every one NADH, we get two and a half ATP. So with two NADHs here, those travel to the electron transport chain and drop off those hydrogens. So at two NADHs at two and a half a piece, we end up with five ATP. Ultimately, we end up with pyruvate. And again, this is an oxidative process.

So those pyruvates are converted into acetyl-CoA during that step. That kind of... step in between glycolysis and the Krebs cycle, two NADHs are produced, one for each pyruvate. So we got two more NADHs here and at two and a half ATP per, that gives us another five ATP. So now we're entering the Krebs cycle because only acetyl-CoA can enter the Krebs cycle.

So what we have here and for the rest of this image down here in the bottom, this is the total. So this is for... both spins for two spins of the Krebs cycle.

So our totals are six and ADHs at two and a half ATP per. We get 15 ATP. We produce one FADH for every turn of the Krebs cycle.

So we end up with two and at one and a half ATP per FADH, we end up with three ATP from those sources. And then we also, you remember the GTP to ATP, we're just going to count them as ATP, that's substrate level phosphorylation, and we get one for each turn. So we end up with two more ATP down there at the bottom. So the total energy yield from the complete oxidative metabolism of a glucose is 32 ATP. One thing I want to point out here is all of this inside of this green box, These are all your NADHs and FADHs.

And so these are clumped together here just to illustrate that all of these, all of this ATP is being processed, is being synthesized in the electron transport chain. And so outside of this box you see that we get two here and two here. That's only four of the 32 ATP that are not coming from the electron transport chain. Most of the ATP we're getting from this oxidative system is actually coming from the processes that happen within this electron transport chain.

So here's a different way to look at the breakdown of net totals. It doesn't really illustrate where all these are coming from. It's just kind of the big picture.

So we've got a breakdown of our net totals for ATP for the, again, look at the top, oxidation of carbohydrate. So aerobic process. So from glycolysis, we get either two or three ATP.

We get two if we start with glucose. We get three if we start with glycogen. We get the ATP from substrate level phosphorylation from the Krebs cycle. So we get two ATP, one from each turn.

We have a cumulative total of 10 NADHs. So 10 times two and a half because we get two and a half ATP for every one NADH gives us 25 ATP. From our two FADHs at one and a half ATP each, we get three ATP.

So the net totals for glucose, 32 ATP, glycogen 33, just because of that difference in the energy input phase in glycolysis.

Transcript for:Understanding the Oxidative Energy System

Transcript for:
Understanding the Oxidative Energy System