Glycolysis and Gluconeogenesis Overview

Hi and welcome to lecture 10 for biochemistry 423 going over chapter 16 and 17 on glycolysis and gluconeogenesis. I have this youtube video that I like from this guy that I will put a link to on the canvas course and maybe play for you guys in class tomorrow. So let's get started here. I won't go through it right now for the video. So the learning objectives for both chapter 16 and 17 are together starting with glycolysis describe how atp is generated in glycolysis so stage one requires two atp input stage two generates four atp so you net two atp total per glucose molecule so there's a series of enzyme catalyzed reactions which generate atp usable energy and nadh which is an electron transport an electron transporter to the electron transport chain second objective explain why the regeneration of nad plus is crucial for fermentations So NAD plus is a finite resource needed for the oxidation of G3P or glyceraldehyde 3-phosphate into pyruvate. So this is regenerated through conversion of pyruvate to either ethanol, alcohol fermentation or lactic acid. OK, in lactic acid fermentation. This allows for a generation of NAD plus to continue the glycolytic cycle. So if we don't have fermentation, right, basically under. under certain conditions right if we don't have enough oxygen then we wouldn't be able to generate energy but in this way we would generate nad plus so that we can continue to do anaerobic respiration through glycolysis okay the first objective for chapter 17 describe how gluconeogenesis is powered in the cell so decarboxylation reactions is essentially how this gets powered in the cell often drive different reactions that are otherwise highly endergonic So just like in glycolysis and gluconeogenesis, energetically favorable reactions are coupled with energetically favorable ones to drive spontaneity of the process. Describe how the coordinated regulation of glycolysis and gluconeogenesis occurs. So this is reciprocal regulation, okay? And we'll talk about coordinating this in all the different regulators. So within a cell, one pathway is relatively inactive while the other one is highly active, okay? So this is how we coordinate them. We don't... do them in the same cell. You wouldn't be doing glycolysis in the same cell you were doing gluconeogenesis because a lot of these reactions are driven by concentration of product and reactant and the function of particular enzymes. So if you had to reduce the function of one enzyme while also increasing the function of another enzyme, but then you had too much of one concentration for the other, right? You see how you can't do them in both directions within the same cell. So that doesn't happen when glucose is abundant glycolysis will predominate and when glucose is scarce gluconeogenesis will take over within a particular cell now there's also whole body coordination which isn't really reciprocal regulation okay but it does describe a way that we do both of these at the same time because it is necessary for us to do both of these at the same time even though we don't do it within a particular cell we do do it in different parts of our body A few other things to know here that aren't necessarily on the specific aims, but understand the general flow of glycolysis and gluconeogenesis. You don't need to know every structure and every name or every enzyme that catalyzes each step, but you should be able to identify the key players in the key steps that are different between the two. Okay, so glycolysis. What is glycolysis? So glycolysis is a sequence of reaction that converts one molecule of glucose into two molecules of pyruvate. while generating atp okay now these molecules i put up here are not pyruvate what are these molecules okay well before we get there first and foremost the primary function of glycolysis is the generation of atp so we do glycolysis to generate atp that's the main function okay it provides quick easily accessible energy from a very quick and easily accessible energy source one of the most abundant ones glucose The byproducts of glycolysis are also important for providing simple building blocks for biosynthesis. This is why pathways are both catabolic and anabolic. This is why they are amphipathic. Okay. Sorry. Is that what I said? I mean amphibolic, not amphipathic. sorry um okay so what happens in stage one stage one is the conversion of glucose okay into g3p glyceraldehyde 3-phosphate and or dihydroxyacetone phosphate or dhap okay we typically think of it as glyceraldehyde 3-phosphate even though we make a lot more dhap okay we have enzymes that interconvert glyceraldehyde 3-phosphate and dhap And so even when we have a lot more DHAP, we convert it into glyceraldehyde 3-phosphate. And glyceraldehyde 3-phosphate is what ultimately goes into stage 2 of glycolysis. So as we use up glyceraldehyde 3-phosphate in stage 2 of glycolysis, that DHAP gets converted into glyceraldehyde 3-phosphate. So stage 2 is the progressive oxidation of G3P into pyruvate. So this is all of glycolysis. We are... essentially converting glucose into two molecules of pyruvate we break it up into two stages we think of stage one as the energy investment stage okay so we invest energy in this and then we think of stage two as where we get energy out of it and we'll look at that in more detail so first just really quick so just to review here we're talking about carbohydrates digestion of carbohydrates remember carbohydrates get broken down starting in the mouth with alpha amylase and then we have a bunch of different specific monosaccharide or sorry enzymes that function on polysaccharides of different sizes whether they be disaccharides or trisaccharides or larger polysaccharides including lactose and sucrose each of these basically has their own particular enzyme that digests them further into simple sugars right and then those simple sugars glucose galactose or fructose can all be absorbed by the intestinal cells and ultimately be put into the bloodstream okay all right so looking at glycolysis this is all of glycolysis written out here we have stage one in pink and stage two in yellow okay we have every single intermediate here that gets formed in each stage we also have all of the different names of them right so glucose here glucose six phosphate fructose six phosphate fructose one six bisphosphate glyceraldehyde three phosphate notice dihydroxyacetone so we're making a large portion of our fructose one six bisphosphate and breaking it into dihydroxyphosphate um dihydroxyacetone phosphate but since glyceraldehyde 3 phosphate is what gets pushed into stage two when we push glyceraldehyde 3 phosphate into stage two right we drive that reaction towards making more glyceraldehyde 3 phosphate so we go from glyceraldehyde 3 phosphate into one three is phosphoglycerate three phosphoglycerate into two phosphoglycerate right phosphenylpipirate and finally pyruvate Okay, real quick, notice that basically all we're doing here is we're adding phosphates, okay, and then we are using the energy from the added phosphates, and we're using the phosphates themselves to generate more ATP. So we add phosphates, right, using ATP in stage one. That's why it's our energy investment stage. And then we're breaking apart the molecule. And we are using, right, the fact that these are higher phosphoryl transfer potential molecules, 1,3-bisphosphoglycerate is an example, phosphoenolpyruvate, in order to generate ATP. And since we've broken it apart into two different molecules here, okay, we actually have more phosphates, right? So we break glyceraldehyde 3-phosphate, we add another phosphate to it. Okay, and then we can use that to generate 4 ATP. So we have an investment of 2 ATP in stage 1. Stage 2 happens twice, and we generate 4 ATP total. Notice we also generate an NADH in the conversion of glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate. This is another energy-carrying molecule that's just different than ATP. Okay, so let's look at it stage by stage. So if we look at stage 1, Okay, the first reaction is hexokinase converting glucose into glucose 6-phosphate. This is one of the key regulatory steps, okay? We have an ATP investment, so this is normally glucose to glucose 6-phosphate, highly endergonic, okay? But we couple it with this highly exergonic reaction of ATP's conversion to ATP in order to drive glucose into glucose 6-phosphate, okay? so phosphorylation why is this a regulatory step why is it so important phosphorylation traps glucose inside the cell so glucose freely moves in and outside of cells through glucose transporters But phosphorylated glucose, glucose 6-phosphate, cannot go through those same transporters. And so once it gets converted into glucose 6-phosphate, it's trapped. Now you have trapped that glucose inside the cell until you dephosphorylate it. So kinases add phosphate groups, also require divalent cations. So hexokinase functions to add a phosphate. Kinases adds phosphates. So if it says kinase, you know you're adding a phosphate. here okay then we have phosphoglucoisomerase isomerization to furanose sugar allows for easier cleavage to a three carbon compound in later steps so we convert glucose six phosphate into a fructose six phosphate okay we turn it into a furanose sugar now this isomerase is a reversible reaction so it's driven completely by buildup of product or reactant on either side okay and so what happens here well if we have a you buildup of glucose 6-phosphate, right, because we've trapped glucose in the cell. So you imagine you have a high blood glucose. Blood glucose means that glucose goes inside your cells. You're trapping glucose. You have a buildup of glucose 6-phosphate. That's going to drive that reaction towards fructose 6-phosphate, okay? Now you're making more fructose 6-phosphate as you have a buildup of glucose 6-phosphate, okay? So let's imagine a world where phosphofructokinase, which is the next step that we'll learn about, okay? Let's imagine a world where you regulate phosphofructokinase and you prevent its function. Now fructose 6-phosphate can't be converted into fructose 1,6-bisphosphate. And so you get a buildup of fructose 6-phosphate. Well, if you have a buildup of fructose 6-phosphate, that means you're going to be converting more fructose 6-phosphate into glucose 6-phosphate. Okay? This is something to think about as you're thinking about reversible reaction and regulations and pathways. Okay, so speaking of phosphofructokinase, this is our next stop in stage one. This is the primary central regulator enzyme of all of glycolysis. Okay, we would sort of consider this the point of no return. Okay, this is the highest energy investment that we have, right? We've invested two full ATPs once we get past phosphofructokinase. And so going backwards from this case, would be the most amount of energy loss and so it makes sense to regulate this enzyme highly hexokinase is also one of the central regulators phosphor fructokinase is more central regulation but hexokinase is also regulated right because this is the first energy investment step okay and also you can regulate it because let's pretend you don't want to trap glucose we already have enough glucose in the cell regulating hexokinase means you stop the trapping of glucose in the cell and so that's where you can regulate this pathway if you stop glucose from getting trapped in the cell you don't go don't go through the rest of the steps okay so phosphofructokinase otherwise known as pfk catalyzes an irreversible reaction this is the key regulatory point again requires atp input okay so we learned about a couple of other sugars from the diet that you can get galactose fructose okay Galactose essentially has a separate enzyme that directly isomerizes and phosphorylates it into glucose 6-phosphate. Fructose has something that directly phosphorylates it into fructose 6-phosphate. And so galactose and fructose essentially enter into glycolysis at these levels. So both of them produce the same amount of energy that glucose would, right? Because galactose... requires an ATP input to be converted to glucose 6-phosphate, and fructose requires an ATP input to be turned into fructose 6-phosphate. So fructose can also enter through direct cleavage into DHAP, well, direct cleavage and phosphorylation, right, into either DHAP or G3P, but we won't go over that right now. Okay, so really, I just wanted to indicate if we're talking about galactose or we're talking about fructose. and we're talking about energy yields from them they're virtually identical to glucose okay so now we're at dihydroxyacetone and glyceraldehyde 3 phosphate so now we're getting into stage two and stage two starts when we convert glyceraldehyde 3 phosphate into 1 3 bisphosphoglycerate right so let's talk about this stage two so stage two series of enzymes catalyze reactions which generate atp and nadh that first step generates an NADH through subsequent oxidation reactions to pyruvate. Okay, so what do we get out of it? Well, our net ATP out of it, we use 2-ATP in stage one. We generate 2 ATP in stage 2, but we generate that twice because we generate 2 for each 3-carbon molecule. So each conversion of G3P into pyruvate generates 2 ATP, getting us a net 4 ATP from stage 2. And 2 ATP is generated per glucose molecule, okay? Because we have positive 4 in stage 2 and negative 2 in stage 1. Minus 2 plus 4 is plus 2. So each round of glycolysis nets. two ATPs. We also get two NADH molecules out of it as well, and we'll talk about what energy yield we get from NADH later on. So here is stage two, okay? So notice, I showed this chart before about the centrality of ATP in the phosphoryl transfer potential range. So ATP is here. ATP, right, can donate phosphates to glucose to make glucose 6-phosphate. can donate phosphates to glycerol to make glycerol 3-phosphate, G3P. It can then also accept phosphates from things like 1,3-phosphoglycerate, which is a higher phosphoryl transfer potential. So we essentially generate higher phosphoryl transfer potential molecules and then use them to regenerate ATP. And this is why ATP is such a great currency. You'll also notice phosphoenolpyruvate. is also a higher phosphoryl transfer potential, which is why its conversion to pyruvate generates another ATP. Okay, so let's look at fermentation here. So what happens after we've made pyruvate, we have some steps afterwards. So in order for glycolysis to continue, right, we need to be able to regenerate a finite resource, and that finite resource is NAD+. Why is NAD+, a finite resource? So we generate NADH and we use up NAD+. And NAD+, we can only generate NADH if we have NAD+. If we use up all our NAD+, we don't have an electronic scepter to generate NADH. And so if we run out of NAD+, we cannot go from stage one to stage two in glycolysis. And we would essentially be stuck at the maximal energy input without getting any energy out. So what does fermentation help us do? It helps us regenerate NAD+, so that we can do the conversion of glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate. So it's generated through conversion of pyruvate to either ethanol and alcohol fermentation or lactic acid and lactic fermentation like we have in humans. Okay? So that is what fermentation is essentially good for. Okay? And we... can't do an infinite amount of fermentation, right? Organisms that produce ethanol, and ethanol is highly toxic to most organisms. So if you produce too much ethanol, you end up killing a lot of your cells. And just like in humans, if we produce too much lactate, we lower the local pH, this can be damaging to tissues. And so we don't generate an infinite amount. So we can't just infinitely do fermentation either. Okay. We'll learn more about conversion of pyruvate and acetyl-CoA in the subsequent lecture. okay so how does this look glucose we input atp to make one one six sorry fructose one six bisphosphate or bisphospho yeah bisphosphate and then we convert that into three carbon molecules we take those three carbon molecules we generate any dh we generate some atps throughout okay and so we net two atps and then we can continue to do this process of stage two by regenerating nad plus through fermentation. So conversion of pyruvate and acetyl-CoA, right, which is this step back here, right, this leads to further extraction of energy through combustion of CO2 and H2O in the citric acid cycle, which again we'll learn about in the next lecture. Okay, so how is glycolysis regulated? Okay, so if we're talking about in the muscle, it's different in the muscle than it is in the liver. And that's because the liver is central for energy processing and energy storage. So things that happen in the muscle happen a little bit different in the liver. Things that happen in other tissues that aren't the liver tend to be different. And high energy uses tissues tend to be different than regular tissues as well. So muscle and brain tend to be the highest usage energy. And so we can sort of think of this as what's happening in those high glycolysis need tissues. So how is it regulated in muscle? Well, it's regulated at three key steps. The first one is hexokinase, which I mentioned before. The second one is phosphofructokinase, and the third one is actually the last step of stage two in pyruvate kinase. Okay, so how is hexokinase regulated? Well, the function of hexokinase is inhibited by its product, glucose 6-phosphate. This means that if we have a buildup of glucose 6-phosphate, right, it will inhibit the function of hexokinase, thereby you won't get any more trapping of glucose. This is sort of a stop to, hey, we've trapped enough glucose, stop trapping glucose, and glucose won't be trapped in that cell anymore. It is also inhibited, right? So... If we inhibit PFK, then we lead to a buildup of fructose 6-phosphate. As we build up fructose 6-phosphate, that drives this reversible reaction to build up glucose 6-phosphate, which means that we are inhibiting hexokinase and not trapping glucose. So indirectly, any loss of function of PFK indirectly regulates hexokinase or downregulates hexokinase, which basically means that if we aren't doing the point of no return, we don't want to do the first step as much either. Okay, phosphofructokinase is the next step on our list. How is it regulated? So phosphofructokinase, if we have high ATP levels, ATP will allosterically inhibit phosphofructokinase's function. So the higher levels of ATP we have, the less function we have of phosphofructokinase. This makes sense, right? If we push to the point of no return, the whole point... point of this process is to build up ATP. And so the end product of glycolysis, for the most part, is ATP. When we have enough ATP, we want to downregulate this process. We downregulate phosphofructokinase. We also will indirectly downregulate hexokinase. EMP binds to the same allosteric site as ATP, but it does not inhibit. so what this means is that in low energy conditions right we prevent the allosteric regulation which means pfk can now be fully functional when we are in low energy conditions again this makes sense we want to be doing glycolysis to generate an atp if we have a high buildup of amp that means atp is low therefore we will do more glycolysis So really, the decrease in ATP to AMP ratio is what increases enzyme activity. ATP goes down, increased activity. AMP goes up, right? We get increased activity. So low pH also inhibits PFK activity. So this prevents damage from too much lactic acid fermentation. This is why we can't do an infinite amount of fermentation. we would build up that lack of lactic acid or we would build up ethanol so if we have a low ph from buildup of lactate pfk is down regulated we down regulate all of glycolysis okay finally pyruvate kinase is the last key regulatory enzyme so high atp allosterically inhibits similar to pfk fructose 1 6 bisphosphate activates ah okay so this is also partially why phosphofructokinase is the central regulator. If we go past the point of no return to fructose 1,6-bisphosphate, we are at our highest energy investment. We want to get something back out of it. So if we get this high energy molecule, we want to make sure that we are going through to the end. So we will activate pyruvate kinase to push through to make pyruvate and generate ATP through stage 2. All of these things I said, this is a recurring theme in regulation of metabolic processes. The end product of a pathway often has feedback inhibition effects on the system, and for irreversible steps, often the product of that step directly inhibits the enzyme that catalyzes it. You'll see this theme come up in many different pathways. What does that end up looking like? Let's look at two different conditions in the muscle. On the left, we have at rest. on the right we have during exercise so on the left we have we are abundant in energy and on the right we have we are energy depleted we are using our energy so if we have abundant energy what happens well we have a lot of glucose so if we have a lot of glucose we'll trap a lot of glucose if we trap a lot of glucose we will inhibit further trapping of glucose if we have a lot of glucose we likely have a lot of atp if we have a lot of atp we've likely gone through this process a lot atp will directly inhibit remember that atp amp ratio will directly inhibit pfk allosterically it will also directly inhibit pyruvate kinase activity this is essentially saying we have enough energy we have enough glucose Instead of doing glycolysis, we will actually convert our glucose 6-phosphate into glycogen because we can't do other stuff with it because we can't push through. PFK isn't functioning. Hyruvate kinase isn't functioning. Now, during exercise, we've depleted our energy. We have a low ATP to high AMP ratio. So low levels of ATP, high levels of AMP. We will activate PFK. If we activate PFK, that pushes fructose 6-phosphate into this high-energy state. That high-energy state molecule will activate pyruvate kinase so that we push through all of stage 2, and then we can do lactic fermentation or we can be made an acetyl-CoA, depending on if we're going to do more glycolysis. If we're going to continue to do glycolysis, we'll need lactate to regenerate the NAD8, sorry, the NAD+, that gets generated after fructose 1,6-bisphosphate gets broken apart. and then glyceraldehyde 3-phosphate gets turned into 1,3-bisphosphoglycerate, okay? Or we can go into acetyl-CoA if we have more steady, sustained energy needs. But if we need immediate energy, we'll continue to do glycolysis and fermentation. So what's different about the liver compared to the muscle? Let's take a look. So the liver has actually two different enzymes that will trap glucose. It has hexokinase, which will trap glucose. but hexokinase gets down regulated when you have a buildup of glucose 6 phosphate glucokinase okay so the liver uses this enzyme primarily to phosphorylate glucose in the liver why is that well the liver doesn't use a lot of glucose for metabolic energy the liver is generating very small amounts of atp because it doesn't need as much atp as say places like the muscle but you're doing a lot of atp usage So instead, hexokinase is usually down-regulated to the point of non-functionality in the liver, unless we're really low on blood glucose and it needs to take it in. And so since hexokinase isn't functioning, we still want to trap glucose in the liver. Why? Because the liver is central to energy metabolism and storage. And so even though we're not trapping it to put it into glycolysis, we are trapping it so that we can use it for energy storage. So the Km of glucokinase is very high, okay, compared to hexokinase. So glucose has to be way more abundant for glucokinase to work. So normally in the liver, we want to be sending out glucose. We are typically converting glucose 6-phosphate into glucose in the liver. so that we can send it to other parts of the body okay but if we are in extremely high glucose excess we still want to trap glucose in the liver so that we can convert it into glycogen so even though this has a very high km all that means is that it functions only at higher abundancy of glucose so brain and muscle have dibs on glucose before liver cells essentially Okay, what's different about phosphofructokinase in the liver? Well, it's got the same regulatory mechanisms, but there's not usually a need for rapid APT production in the liver compared to the muscle. So another thing that is inhibited by is citrate in the liver. So citrate is an intermediate of the citric acid cycle, right? It's what gets made in the first step of the citric acid cycle and why it gets its name. And a buildup of citrate inhibits PFK function. Why does citrate prevent PFK function? Okay, so citrate will prevent PFK function because a buildup of citrate implies that we have done enough glycolysis to make enough citrate for the liver's needs. And so we don't need to make any more PFK because the largest portion of pyruvate that gets made in the liver is gonna be converted into acetyl-CoA and ultimately become. citrate in the citric acid cycle. So if we have too much citrate, we don't need to make any more. Okay, one other major difference in the liver is there is a second PFK enzyme. So in the muscle, there's only a single PFK enzyme, and on the liver, we have two. And we'll consider the second one, PFK2, versus the first one is PFK1. So this PFK2 enzyme in the liver converts some fructose 6-phosphate into fructose 2,6-bisphosphate. Remember, PFK1 converts... F6P into F1 6P, PFK2 phosphorylates at a different site. And so it becomes F2 6BP, that's fructose 2,6-bisphosphate. And this is a potent activator of PFK1. This might seem strange, okay, but let's think through why this might be true. So if we typically have fairly low and steady PFK activity in the liver, because we only want to make enough pyruvate, right, to meet very minor energy needs from that, and the primary function of glycolysis in the liver is going largely to be making acetyl-CoA to make citrate, okay? Now we're at this low level of function, okay? However, every once in a while, we may need to activate glycolysis very quickly because we're at that low level. But let's say we deplete our citrate or we really do need some immediate ATP from glycolysis in the liver. It does happen from time to time, right? So let's pretend Because we're in this low functioning state, right, we're normally high glucose level, glucokinase is functioning slowly compared to hexokinase. That means that phosphofructokinase is sort of at a low level of function. We typically are at high energy state. However, we can need to make more of any particular thing on short notice. So PFK2 is an enzyme that can be active. reactivated to make this fructose 2,6-bisphosphate, which then hyperactivates PFK1. So it means that normally in the liver, glycolysis is at a very low level, but we have a switch that can quickly turn it on and hyperactivate it. Okay, why might we need that? We can talk about that another time. Okay, pyruvate kinase finally differences in the liver. There's an isoform in the liver called... L-form for liver form versus M-form in the muscle. What is the differences here? Well, same thing, ATP, high ATP allosterically inhibits this. Fructose 1,6-bisphosphate activates this, same thing. This is also allosterically hindered by alanine. Why is that? Well, one of the major things, the reasons we do glycolysis in the liver isn't to generate a bunch of ATP typically, but it's to make things like pyruvate or citrate, et cetera. So if we've made enough pyruvate... right much of that pyruvate can get converted into alanine and when we've made enough alanine right then we don't need to go through and make more pyruvate and so since it's a simple conversion product of pyruvate this signals to shut off pyruvate production which down regulates pyruvate kinase okay so that is glycolysis and regulation of glycolysis now let's look at gluconeogenesis so gluconeogenesis synthesis of glucose from non-carbohydrate precursors. Major site of gluconeogenesis is the liver, and we convert pyruvate to glucose in it. So all I've done here is I've gone, gluconeogenesis is basically just glycolysis in reverse, and I'll show you what I mean by that. It's not exact, but it's close. So if we look at them side by side, and we start at pyruvate and gluconeogenesis on the left here, we see that our endpoint... for glycolysis is pyruvate we go in glycolysis we convert from phosphoenolpyruvate whereas pyruvate here the first step is to make oxaloacetate so this conversion of pyruvate to phosphoenolpyruvate is highly endergonic it's one of the most endergonic reactions that we have here in metabolism okay and so it's high energy input in order to make phosphoenolpyruvate from pyruvate. And in order to do it, we actually need an extra step. And so what we do is we use ATP. We not only use energy input from ATP and GTP, which is another nucleotide triphosphate that uses energy or can be used as an energy currency. So not only do we input multiple phosphate breakage energies, but we also couple that with carboxylating. So adding a carbon dioxide to pyruvate, which we can then use in a second step to decarboxylate. Okay, why would we add a carbon dioxide and then remove a carbon dioxide in order to drive the reaction? Well, essentially, we're using the energy of entropy here. So we create a molecule that is higher energy by inputting ATP. We couple that. increase in energy to also add a CO2. And when we convert that oxaloacetate into phosphoenolpyruvate and CO2, we have an increase in entropy. Okay, and if we are increasing entropy, that is another way to drive reactions. So decarboxylation reactions, because they increase entropy of the system, you go from one molecule to two molecules, okay, CO2 and phosphoenolpyruvate. You can use that to drive reactions that would otherwise maybe just sort of barely happen energetically because you are driving entropy up. you can take small exergonic reactions and make them happen more easily. So the conversion of oxaloacetate to phosphenolpyruvate is not nearly as high energy need as the conversion of pyruvate to oxaloacetate, but coupling it with a GTP conversion to a GDP, as well as coupling it with a decarboxylation, means that it is just exergonic enough when it's coupled. that that change in entropy will drive it forward more spontaneously. Okay, so essentially the biggest differences here are that the conversion of pyruvate to phosphoenopyruvate, the reverse of the last reaction, needs a second step and needs an extra GTP input as well as needs to have a decarboxylation. So instead of being pyruvate kinase, the reverse reaction from pyruvate to phosphoenopyruvate is two steps that requires two different enzymes. Now notice, all of the steps are the same, and all of them use the same enzymes. Because remember, enzymes increase the reaction rate of both the forward and the reverse reaction. So if we change the conditions to be favorable directionally, that enzyme will decrease the activation energy of both the forward and reverse reaction thereby increasing the rate of reaction in both directions and so all we need to do is change the conditions so a buildup of phosphoenolpyruvate will cause spontaneously the conversion by enolase into two phosphoglycerate we have phosphoglucomutase in both we have phosphoglycerate kinase in both okay instead of here we generate an atp we have to use an atp 1,3-bisphosphoglycerate is in both. That gets converted into glyceraldehyde 3-phosphate in both. Okay. Glyceraldehyde 3-phosphate gets converted to fructose 1,6-bisphosphate in both. So essentially, you'll notice the differences only at the regulatory enzymes. So remember, hexokinase, phosphofructokinase, or PFK. and pyruvate kinase were the key regulatory enzymes of glycolysis and those enzymes are not used in gluconeogenesis instead of pyruvate kinase we have pyruvate carboxylase and phosphoenol pyruvate carboxykinase so we have these two enzymes to substitute for the reverse reaction of pyruvate kinase and then all the reactions are the same just in reverse until we get to the analogous reverse reaction from pfk instead of pfk the reverse reaction from fructose 1 6 bisphosphate is catalyzed by fructose 1 6 bisphosphatase okay and once we get to hexokinase instead of hexokinase we have glucose 6 phosphatase which removes the phosphate from glucose 6 phosphate so gluconeogenesis glycolysis are reverse reciprocally regulated reactions these are the differences Just to review, analogous enzymes for the reverse reaction in each case. The regulatory enzymes for gluconeogenesis are the same steps as they are in glycolysis. It's just the enzymes are different. So hexokinase is a regulated enzyme in glycolysis. The counterpart in gluconeogenesis, glucose 6-phosphatase, also one of the key regulatory enzymes. PFK is analog, is fructose 1,6-bisphosphatase, and pyruvate kinase has these two enzymes in order to catalyze the two-step reaction. So if we look at this gluconeogenesis, this is just the same information only on the table that I've given you. So key irreversible step differences. Pyruvate kinase, instead of pyruvate kinase, we have these two enzymes. These are the reactions they catalyze. PFK, it's analog is this, catalyzes this reaction. hexokinase instead we have glucose phosphatase catalyzes this so you should know this i just put it in a table you don't have to know the table that same information is here i just put it on a table for you okay all right so a little bit more information just to give details what is the conversion of pyruvate and oxaloacetate look like so we have pyruvate combined with co2 we use the conversion of atp to adp and a phosphate in order to drive the pyruvate carboxylase to form oxaloacetate okay so that energy input from atp allows us to add this carbon dioxide to pyruvate okay and then We can use GTP in order to add a phosphate, and we can use the decarboxylation in order to drive entropy. So this very tiny exergonic reaction happens more readily because of the increase in entropy. We go from one molecule of oxaloacetate to one molecule of phosphoenolpyruvate and one CO2. So two different products here. Or if you want to consider GTP, right, we have two molecules being broken into three molecules so higher entropy so pyruvate carboxylase okay so biotin is a covalently attached prosthetic group that serves as a carrier of activated co2 so we actually don't have just co2 we need an activated form of co2 which is carried by biotin co2 you don't have to memorize this this is just what's actually happening behind the scenes of this reaction and then also phosphoenol pyruvate co2 that was added to pyruvate by pyruvate carboxylase comes off on this step that's what drives this reaction forward through decarboxylation okay so these two reactions if you want to know sort of the net here okay so pyruvate plus atp plus gtp generates phosphoenol pyruvate and phosphate adp gdp as well as two hydrogens so how's gluconeogenesis powered in the cell well addition of phosphoryl groups to pyruvate is highly undergonic okay so If we wanted to add a phosphate group directly, which is basically what phosphoenolpyruvate is, right? Pyruvate plus this phosphate group. So if we wanted to add this directly, it would be 31 kilojoules per mole. Formation of phosphoenolpyruvate from pyruvate is much less endergonic. It's 0.8 kilojoules per mole. And so because we have this very low... right we have we have to input energy right we have to input energy in the form of atp but instead we can drive this forward much more easily because that decarboxylation so decarboxylations often drive reactions that are otherwise highly endergonic so we'll learn a little bit more about this in the citric acid cyclin fatty acid synthesis we have a couple of other examples there okay and then the second reaction here fructose 1 6 bisphosphate is the second regulatory reaction here's more details of it We're just removing a phosphate from fructose 1,6-bisphosphate. Okay. And so finally, what is the net here? Two pyruvates take two ATPs, two GTPs. You also use up to NADHs in order to form one glucose molecule, right? So it's a lot of energy input, right? It costs more energy to make glucose than it does to break it down into pyruvate. And this would make sense. Otherwise, you'd have sort of a perpetual energy machine. because you could just use the energy from glucose to make more glucose and have energy left over. So it must require more energy to build glucose from 2-pyruvates than you generate from glucose to make 2-pyruvates. So just like in glycolysis and gluconeogenesis, energetically unfavorable reactions are coupled with energetically favorable reactions. All of these conversions of ATPs to ADPs or GTPs to GDPs. OK. in order to drive spontaneity of the process this is a very key thing okay so this slide represents the reciprocal regulation of these two things so gluconeogenesis is reciprocally regulated with glycolysis gluconeogenesis and glycolysis are coordinated so that within a cell one pathway is relatively inactive while the other one is highly active the basic premise of reciprocal regulation is that when glucose is abundant glycolysis will predominate when glucose is scarce gluconeogenesis will take over in a nutshell the things that up regulate glycolysis down regulate gluconeogenesis and the things that up regulate gluconeogenesis down regulate glycolysis let's take a look at it we have glucose and then on the left we have the key regulatory steps leading to formation of pyruvate hexakinase isn't in here hexakinase is somewhat up here but hexokinase is just about trapping glucose in the cells so we'll forget about it so these key regulatory steps this is why they're key regulatory steps the things that up and down regulate these cycles or these pathways are at these enzymes. So fructose 2,6-bisphosphate, we'll get into more detail here, but this molecule hyperactivates PFK. Remember, low energy state means that AMP binds to the allosteric binding side of PFK and prevents binding of ATP, so PFK can function better in low energy states. So we have high energy, ATP allosterically downregulates PFK. Citrate buildup also downregulates PFK. pH will downregulate PFK. So if we lower the pH, we'll downregulate PFK. And if we look at the reverse analogous enzyme in gluconeogenesis, okay, F2,6BP, while it will hyperactivate phosphofructokinase, it will deactivate fructose 1,6-bisphosphatase. Low energy means we downregulate gluconeogenesis. If we are in a low energy state, we don't want to be using our energy to build glucose molecules within a cell. if we have a buildup of citrate, okay, we will activate gluconeogenesis. This is reciprocal regulation. What upregulates one, downregulates the other, and vice versa, okay? And we see the same thing in pyruvate kinase and its analogs. Primarily, we see that high energy state downregulates pyruvate kinase and low energy state, okay, here. up regulate or sorry low energy state down regulates gluconeogenesis here also if we have a buildup of acetyl-CoA we want to use some of those carbons in order to generate glucose okay so a lot of what's happening with generating or turning glucose into pyruvate is that conversion of pyruvate and acetyl-CoA if we have too much acetyl-CoA we will say hey let's turn some of that pyruvate into glucose instead of making it into acetylcholine. So you should understand this slide pretty well. Okay, so I talked about this reciprocal regulation. I used an example of in the liver, and I even talked about it on this slide, this fructose 2,6-bisphosphate. So what is fructose 2,6-bisphosphate? So this is an interesting study, and you don't need to memorize this stuff about fructose 2,6-bisphosphate, other than it's a hyperactivator of PFK, and it downregulates. fructose 1 6 bisphosphatase so how does this work okay so let's pretend we are in a glucose abundant state in a glucose abundant state we would imagine we have build up a fructose 6 phosphate because if we're in an energy abundant state okay or a glucose abundant state then we are going to make our glucose into glucose 6 phosphate make our glucose 6 phosphate into fructose 6 phosphate right And so what does PFK do? If we are in a glucose abundant state, then it's going to convert some amount of our fructose 6-phosphate into fructose 2,6-bisphosphate, which will hyperactivate PFK1. Okay, and what is doing that? PFK2 is using, is phosphorylating fructose 6-phosphate to make fructose 2,6-bisphosphate, which then hyperactivates PFK1 to convert fructose 6-phosphate into fructose 1,6-bisphosphate, right? That fructose 1,6-bisphosphate is that highest energy point in glycolysis, okay? So if we have a buildup of glucose, we will want to take that glucose and push it through glycolysis. We do this in the liver, right, which is normally at a low level of glycolysis. Okay, we do this in the liver by making this hyperactivator through this other PFK enzyme. which then says, hey, PFK1 activate, and let's turn that glucose into pyruvate. On the flip side, so the interesting thing about PFK2 is it has multiple different domains. It is a bifunctional kinase, so it's a kinase that uses ATP to add phosphate to fructose 6-phosphate. It also has a phosphatase domain, and when the kinase domain is active, the phosphatase domain is inactive. And when the phosphatase domain is active, the kinase is inactive. If I just said that, essentially when one side is active, the other side is inactive. That is regulated through protein kinase A. We'll learn more about this when we get into gluconeogenesis. Sorry, glycogenolysis and glycogenesis. We'll get more into protein kinase A. But what happens here? So glucagon stimulates pKa when blood glucose is scarce. Okay. So PK is protein kinase A. So signaling when blood glucose is scarce. activates protein kinase A. If blood glucose is scarce, FBPase 2 is very active, which means PFK2 is very inactive. If we don't have much glucose, we turn this switch so that BBPase 2 is active. That's the phosphatase domain. Glycolysis gets inhibited and gluconeogenesis gets stimulated. In this case, where we have low blood glucose, glucose is scarce. we activate fbps2 we inhibit glycolysis and we make more glucose now you might be thinking wait a minute if glucose is scarce and we don't have much glucose why would we want to be using our energy to make glucose remember this is happening in the liver the liver doesn't need much glucose to make energy and low glucose in the liver means it needs to make glucose to transport to tissues that do need it to make energy. So when the liver has low glucose, it makes more glucose. This is counterintuitive because if you think about it in the muscle, when the muscle is at low glucose, it needs to make sure that it is making more energy. And so it needs to activate different things. So if we are at low glucose levels, we need to make glucose. Okay. And we do that by converting the fructose 2,6-bisphosphate. back into fructose 6-phosphate. We convert it back into fructose 6-phosphate, we can convert that fructose 6-phosphate into glucose 6-phosphate, turn the glucose 6-phosphate into glucose. It also, right, directly removes this hyperactivator of PFK. It converts it into normal fructose 6-phosphate. Then, okay, if we have high levels of fructose 6-phosphate, we stimulate another phosphatase that dephosphorylates PFK2. thereby inactivating the fbpase activity and activating the kinase activity so we can convert fructose 6-phosphate into fructose 2 6-bisphosphate and hyperactivate glycolysis so this essentially creates a simple switch related to do we have low glucose or do we have high fructose 6-phosphate remember if we have low glucose right then that will mean that we we'll convert our glucose 6 into glucose we will have less fructose 6-phosphate if we have high glucose we will naturally turn our glucose into glucose 6-phosphate turn our glucose 6-phosphate into fructose 6-phosphate so fructose 6-phosphate concentration is a direct correlation to glucose levels and that's why high levels of this will turn on glycolysis and low levels of glucose will turn on or sorry we'll turn sorry High levels of fructose 6-phosphate will turn on glycolysis, and low levels of glucose will turn on gluconeogenesis in the liver. It creates this switch between these two forms that we can have. Okay, so that is reciprocal regulation, right? This slide right here, this is an example of how things happen differently in the liver. And then we can look at sort of whole body differences and how rather than just reciprocal regulation, things work in concert. So that you can be doing... reciprocally regulated pathways at the same time where they are needed and how does that work okay so if we look in contracting skeletal muscle we have the formation of lactate muscles are working hard they're converting their glucose into pyruvate to generate energy they are using that pyruvate to make lactate to regenerate nad plus so they can use more glucose to generate more pyruvate etc lack can be transported in the blood to the liver where it can be converted back into pyruvate and pyruvate can be converted into glucose in order to send glucose to the muscle and that's the cycle okay so the liver restores the level of glucose necessary for active muscle cells which derive ATP from the glycolytic conversion of glucose to lactate so you do do gluconeogenesis in the liver simultaneously when you're doing glycolysis in the muscle reciprocal regulation okay but at the same time except in different compartments okay so it's good to understand this idea okay and this is a i think brainstorm and share activity that we have i don't have any test your knowledge questions for this chapter specifically um one suggestion that i would make is to uh fill in the glycolysis chart, which I may provide for you on Canvas. And that will end the lecture.

So the learning objectives for both chapter 16 and 17 are together starting with glycolysis describe how atp is generated in glycolysis so stage one requires two atp input stage two generates four atp so you net two atp total per glucose molecule so there's a series of enzyme catalyzed reactions which generate atp usable energy and nadh which is an electron transport an electron transporter to the electron transport chain second objective explain why the regeneration of nad plus is crucial for fermentations So NAD plus is a finite resource needed for the oxidation of G3P or glyceraldehyde 3-phosphate into pyruvate. So this is regenerated through conversion of pyruvate to either ethanol, alcohol fermentation or lactic acid. OK, in lactic acid fermentation. This allows for a generation of NAD plus to continue the glycolytic cycle.

So if we don't have fermentation, right, basically under. under certain conditions right if we don't have enough oxygen then we wouldn't be able to generate energy but in this way we would generate nad plus so that we can continue to do anaerobic respiration through glycolysis okay the first objective for chapter 17 describe how gluconeogenesis is powered in the cell so decarboxylation reactions is essentially how this gets powered in the cell often drive different reactions that are otherwise highly endergonic So just like in glycolysis and gluconeogenesis, energetically favorable reactions are coupled with energetically favorable ones to drive spontaneity of the process. Describe how the coordinated regulation of glycolysis and gluconeogenesis occurs.

So this is reciprocal regulation, okay? And we'll talk about coordinating this in all the different regulators. So within a cell, one pathway is relatively inactive while the other one is highly active, okay?

So this is how we coordinate them. We don't... do them in the same cell.

You wouldn't be doing glycolysis in the same cell you were doing gluconeogenesis because a lot of these reactions are driven by concentration of product and reactant and the function of particular enzymes. So if you had to reduce the function of one enzyme while also increasing the function of another enzyme, but then you had too much of one concentration for the other, right? You see how you can't do them in both directions within the same cell.

So that doesn't happen when glucose is abundant glycolysis will predominate and when glucose is scarce gluconeogenesis will take over within a particular cell now there's also whole body coordination which isn't really reciprocal regulation okay but it does describe a way that we do both of these at the same time because it is necessary for us to do both of these at the same time even though we don't do it within a particular cell we do do it in different parts of our body A few other things to know here that aren't necessarily on the specific aims, but understand the general flow of glycolysis and gluconeogenesis. You don't need to know every structure and every name or every enzyme that catalyzes each step, but you should be able to identify the key players in the key steps that are different between the two. Okay, so glycolysis.

What is glycolysis? So glycolysis is a sequence of reaction that converts one molecule of glucose into two molecules of pyruvate. while generating atp okay now these molecules i put up here are not pyruvate what are these molecules okay well before we get there first and foremost the primary function of glycolysis is the generation of atp so we do glycolysis to generate atp that's the main function okay it provides quick easily accessible energy from a very quick and easily accessible energy source one of the most abundant ones glucose The byproducts of glycolysis are also important for providing simple building blocks for biosynthesis. This is why pathways are both catabolic and anabolic.

This is why they are amphipathic. Okay. Sorry.

Is that what I said? I mean amphibolic, not amphipathic. sorry um okay so what happens in stage one stage one is the conversion of glucose okay into g3p glyceraldehyde 3-phosphate and or dihydroxyacetone phosphate or dhap okay we typically think of it as glyceraldehyde 3-phosphate even though we make a lot more dhap okay we have enzymes that interconvert glyceraldehyde 3-phosphate and dhap And so even when we have a lot more DHAP, we convert it into glyceraldehyde 3-phosphate. And glyceraldehyde 3-phosphate is what ultimately goes into stage 2 of glycolysis. So as we use up glyceraldehyde 3-phosphate in stage 2 of glycolysis, that DHAP gets converted into glyceraldehyde 3-phosphate.

So stage 2 is the progressive oxidation of G3P into pyruvate. So this is all of glycolysis. We are... essentially converting glucose into two molecules of pyruvate we break it up into two stages we think of stage one as the energy investment stage okay so we invest energy in this and then we think of stage two as where we get energy out of it and we'll look at that in more detail so first just really quick so just to review here we're talking about carbohydrates digestion of carbohydrates remember carbohydrates get broken down starting in the mouth with alpha amylase and then we have a bunch of different specific monosaccharide or sorry enzymes that function on polysaccharides of different sizes whether they be disaccharides or trisaccharides or larger polysaccharides including lactose and sucrose each of these basically has their own particular enzyme that digests them further into simple sugars right and then those simple sugars glucose galactose or fructose can all be absorbed by the intestinal cells and ultimately be put into the bloodstream okay all right so looking at glycolysis this is all of glycolysis written out here we have stage one in pink and stage two in yellow okay we have every single intermediate here that gets formed in each stage we also have all of the different names of them right so glucose here glucose six phosphate fructose six phosphate fructose one six bisphosphate glyceraldehyde three phosphate notice dihydroxyacetone so we're making a large portion of our fructose one six bisphosphate and breaking it into dihydroxyphosphate um dihydroxyacetone phosphate but since glyceraldehyde 3 phosphate is what gets pushed into stage two when we push glyceraldehyde 3 phosphate into stage two right we drive that reaction towards making more glyceraldehyde 3 phosphate so we go from glyceraldehyde 3 phosphate into one three is phosphoglycerate three phosphoglycerate into two phosphoglycerate right phosphenylpipirate and finally pyruvate Okay, real quick, notice that basically all we're doing here is we're adding phosphates, okay, and then we are using the energy from the added phosphates, and we're using the phosphates themselves to generate more ATP. So we add phosphates, right, using ATP in stage one.

That's why it's our energy investment stage. And then we're breaking apart the molecule. And we are using, right, the fact that these are higher phosphoryl transfer potential molecules, 1,3-bisphosphoglycerate is an example, phosphoenolpyruvate, in order to generate ATP. And since we've broken it apart into two different molecules here, okay, we actually have more phosphates, right?

So we break glyceraldehyde 3-phosphate, we add another phosphate to it. Okay, and then we can use that to generate 4 ATP. So we have an investment of 2 ATP in stage 1. Stage 2 happens twice, and we generate 4 ATP total.

Notice we also generate an NADH in the conversion of glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate. This is another energy-carrying molecule that's just different than ATP. Okay, so let's look at it stage by stage. So if we look at stage 1, Okay, the first reaction is hexokinase converting glucose into glucose 6-phosphate. This is one of the key regulatory steps, okay?

We have an ATP investment, so this is normally glucose to glucose 6-phosphate, highly endergonic, okay? But we couple it with this highly exergonic reaction of ATP's conversion to ATP in order to drive glucose into glucose 6-phosphate, okay? so phosphorylation why is this a regulatory step why is it so important phosphorylation traps glucose inside the cell so glucose freely moves in and outside of cells through glucose transporters But phosphorylated glucose, glucose 6-phosphate, cannot go through those same transporters. And so once it gets converted into glucose 6-phosphate, it's trapped.

Now you have trapped that glucose inside the cell until you dephosphorylate it. So kinases add phosphate groups, also require divalent cations. So hexokinase functions to add a phosphate. Kinases adds phosphates. So if it says kinase, you know you're adding a phosphate.

here okay then we have phosphoglucoisomerase isomerization to furanose sugar allows for easier cleavage to a three carbon compound in later steps so we convert glucose six phosphate into a fructose six phosphate okay we turn it into a furanose sugar now this isomerase is a reversible reaction so it's driven completely by buildup of product or reactant on either side okay and so what happens here well if we have a you buildup of glucose 6-phosphate, right, because we've trapped glucose in the cell. So you imagine you have a high blood glucose. Blood glucose means that glucose goes inside your cells. You're trapping glucose. You have a buildup of glucose 6-phosphate.

That's going to drive that reaction towards fructose 6-phosphate, okay? Now you're making more fructose 6-phosphate as you have a buildup of glucose 6-phosphate, okay? So let's imagine a world where phosphofructokinase, which is the next step that we'll learn about, okay?

Let's imagine a world where you regulate phosphofructokinase and you prevent its function. Now fructose 6-phosphate can't be converted into fructose 1,6-bisphosphate. And so you get a buildup of fructose 6-phosphate. Well, if you have a buildup of fructose 6-phosphate, that means you're going to be converting more fructose 6-phosphate into glucose 6-phosphate.

Okay? This is something to think about as you're thinking about reversible reaction and regulations and pathways. Okay, so speaking of phosphofructokinase, this is our next stop in stage one. This is the primary central regulator enzyme of all of glycolysis.

Okay, we would sort of consider this the point of no return. Okay, this is the highest energy investment that we have, right? We've invested two full ATPs once we get past phosphofructokinase. And so going backwards from this case, would be the most amount of energy loss and so it makes sense to regulate this enzyme highly hexokinase is also one of the central regulators phosphor fructokinase is more central regulation but hexokinase is also regulated right because this is the first energy investment step okay and also you can regulate it because let's pretend you don't want to trap glucose we already have enough glucose in the cell regulating hexokinase means you stop the trapping of glucose in the cell and so that's where you can regulate this pathway if you stop glucose from getting trapped in the cell you don't go don't go through the rest of the steps okay so phosphofructokinase otherwise known as pfk catalyzes an irreversible reaction this is the key regulatory point again requires atp input okay so we learned about a couple of other sugars from the diet that you can get galactose fructose okay Galactose essentially has a separate enzyme that directly isomerizes and phosphorylates it into glucose 6-phosphate. Fructose has something that directly phosphorylates it into fructose 6-phosphate.

And so galactose and fructose essentially enter into glycolysis at these levels. So both of them produce the same amount of energy that glucose would, right? Because galactose...

requires an ATP input to be converted to glucose 6-phosphate, and fructose requires an ATP input to be turned into fructose 6-phosphate. So fructose can also enter through direct cleavage into DHAP, well, direct cleavage and phosphorylation, right, into either DHAP or G3P, but we won't go over that right now. Okay, so really, I just wanted to indicate if we're talking about galactose or we're talking about fructose.

and we're talking about energy yields from them they're virtually identical to glucose okay so now we're at dihydroxyacetone and glyceraldehyde 3 phosphate so now we're getting into stage two and stage two starts when we convert glyceraldehyde 3 phosphate into 1 3 bisphosphoglycerate right so let's talk about this stage two so stage two series of enzymes catalyze reactions which generate atp and nadh that first step generates an NADH through subsequent oxidation reactions to pyruvate. Okay, so what do we get out of it? Well, our net ATP out of it, we use 2-ATP in stage one.

We generate 2 ATP in stage 2, but we generate that twice because we generate 2 for each 3-carbon molecule. So each conversion of G3P into pyruvate generates 2 ATP, getting us a net 4 ATP from stage 2. And 2 ATP is generated per glucose molecule, okay? Because we have positive 4 in stage 2 and negative 2 in stage 1. Minus 2 plus 4 is plus 2. So each round of glycolysis nets.

two ATPs. We also get two NADH molecules out of it as well, and we'll talk about what energy yield we get from NADH later on. So here is stage two, okay? So notice, I showed this chart before about the centrality of ATP in the phosphoryl transfer potential range.

So ATP is here. ATP, right, can donate phosphates to glucose to make glucose 6-phosphate. can donate phosphates to glycerol to make glycerol 3-phosphate, G3P. It can then also accept phosphates from things like 1,3-phosphoglycerate, which is a higher phosphoryl transfer potential.

So we essentially generate higher phosphoryl transfer potential molecules and then use them to regenerate ATP. And this is why ATP is such a great currency. You'll also notice phosphoenolpyruvate. is also a higher phosphoryl transfer potential, which is why its conversion to pyruvate generates another ATP.

Okay, so let's look at fermentation here. So what happens after we've made pyruvate, we have some steps afterwards. So in order for glycolysis to continue, right, we need to be able to regenerate a finite resource, and that finite resource is NAD+.

Why is NAD+, a finite resource? So we generate NADH and we use up NAD+. And NAD+, we can only generate NADH if we have NAD+. If we use up all our NAD+, we don't have an electronic scepter to generate NADH. And so if we run out of NAD+, we cannot go from stage one to stage two in glycolysis.

And we would essentially be stuck at the maximal energy input without getting any energy out. So what does fermentation help us do? It helps us regenerate NAD+, so that we can do the conversion of glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate.

So it's generated through conversion of pyruvate to either ethanol and alcohol fermentation or lactic acid and lactic fermentation like we have in humans. Okay? So that is what fermentation is essentially good for.

Okay? And we... can't do an infinite amount of fermentation, right? Organisms that produce ethanol, and ethanol is highly toxic to most organisms.

So if you produce too much ethanol, you end up killing a lot of your cells. And just like in humans, if we produce too much lactate, we lower the local pH, this can be damaging to tissues. And so we don't generate an infinite amount. So we can't just infinitely do fermentation either. Okay.

We'll learn more about conversion of pyruvate and acetyl-CoA in the subsequent lecture. okay so how does this look glucose we input atp to make one one six sorry fructose one six bisphosphate or bisphospho yeah bisphosphate and then we convert that into three carbon molecules we take those three carbon molecules we generate any dh we generate some atps throughout okay and so we net two atps and then we can continue to do this process of stage two by regenerating nad plus through fermentation. So conversion of pyruvate and acetyl-CoA, right, which is this step back here, right, this leads to further extraction of energy through combustion of CO2 and H2O in the citric acid cycle, which again we'll learn about in the next lecture.

Okay, so how is glycolysis regulated? Okay, so if we're talking about in the muscle, it's different in the muscle than it is in the liver. And that's because the liver is central for energy processing and energy storage.

So things that happen in the muscle happen a little bit different in the liver. Things that happen in other tissues that aren't the liver tend to be different. And high energy uses tissues tend to be different than regular tissues as well. So muscle and brain tend to be the highest usage energy.

And so we can sort of think of this as what's happening in those high glycolysis need tissues. So how is it regulated in muscle? Well, it's regulated at three key steps.

The first one is hexokinase, which I mentioned before. The second one is phosphofructokinase, and the third one is actually the last step of stage two in pyruvate kinase. Okay, so how is hexokinase regulated? Well, the function of hexokinase is inhibited by its product, glucose 6-phosphate.

This means that if we have a buildup of glucose 6-phosphate, right, it will inhibit the function of hexokinase, thereby you won't get any more trapping of glucose. This is sort of a stop to, hey, we've trapped enough glucose, stop trapping glucose, and glucose won't be trapped in that cell anymore. It is also inhibited, right?

So... If we inhibit PFK, then we lead to a buildup of fructose 6-phosphate. As we build up fructose 6-phosphate, that drives this reversible reaction to build up glucose 6-phosphate, which means that we are inhibiting hexokinase and not trapping glucose.

So indirectly, any loss of function of PFK indirectly regulates hexokinase or downregulates hexokinase, which basically means that if we aren't doing the point of no return, we don't want to do the first step as much either. Okay, phosphofructokinase is the next step on our list. How is it regulated?

So phosphofructokinase, if we have high ATP levels, ATP will allosterically inhibit phosphofructokinase's function. So the higher levels of ATP we have, the less function we have of phosphofructokinase. This makes sense, right?

If we push to the point of no return, the whole point... point of this process is to build up ATP. And so the end product of glycolysis, for the most part, is ATP.

When we have enough ATP, we want to downregulate this process. We downregulate phosphofructokinase. We also will indirectly downregulate hexokinase.

EMP binds to the same allosteric site as ATP, but it does not inhibit. so what this means is that in low energy conditions right we prevent the allosteric regulation which means pfk can now be fully functional when we are in low energy conditions again this makes sense we want to be doing glycolysis to generate an atp if we have a high buildup of amp that means atp is low therefore we will do more glycolysis So really, the decrease in ATP to AMP ratio is what increases enzyme activity. ATP goes down, increased activity. AMP goes up, right?

We get increased activity. So low pH also inhibits PFK activity. So this prevents damage from too much lactic acid fermentation.

This is why we can't do an infinite amount of fermentation. we would build up that lack of lactic acid or we would build up ethanol so if we have a low ph from buildup of lactate pfk is down regulated we down regulate all of glycolysis okay finally pyruvate kinase is the last key regulatory enzyme so high atp allosterically inhibits similar to pfk fructose 1 6 bisphosphate activates ah okay so this is also partially why phosphofructokinase is the central regulator. If we go past the point of no return to fructose 1,6-bisphosphate, we are at our highest energy investment. We want to get something back out of it.

So if we get this high energy molecule, we want to make sure that we are going through to the end. So we will activate pyruvate kinase to push through to make pyruvate and generate ATP through stage 2. All of these things I said, this is a recurring theme in regulation of metabolic processes. The end product of a pathway often has feedback inhibition effects on the system, and for irreversible steps, often the product of that step directly inhibits the enzyme that catalyzes it.

You'll see this theme come up in many different pathways. What does that end up looking like? Let's look at two different conditions in the muscle. On the left, we have at rest.

on the right we have during exercise so on the left we have we are abundant in energy and on the right we have we are energy depleted we are using our energy so if we have abundant energy what happens well we have a lot of glucose so if we have a lot of glucose we'll trap a lot of glucose if we trap a lot of glucose we will inhibit further trapping of glucose if we have a lot of glucose we likely have a lot of atp if we have a lot of atp we've likely gone through this process a lot atp will directly inhibit remember that atp amp ratio will directly inhibit pfk allosterically it will also directly inhibit pyruvate kinase activity this is essentially saying we have enough energy we have enough glucose Instead of doing glycolysis, we will actually convert our glucose 6-phosphate into glycogen because we can't do other stuff with it because we can't push through. PFK isn't functioning. Hyruvate kinase isn't functioning. Now, during exercise, we've depleted our energy.

We have a low ATP to high AMP ratio. So low levels of ATP, high levels of AMP. We will activate PFK. If we activate PFK, that pushes fructose 6-phosphate into this high-energy state. That high-energy state molecule will activate pyruvate kinase so that we push through all of stage 2, and then we can do lactic fermentation or we can be made an acetyl-CoA, depending on if we're going to do more glycolysis.

If we're going to continue to do glycolysis, we'll need lactate to regenerate the NAD8, sorry, the NAD+, that gets generated after fructose 1,6-bisphosphate gets broken apart. and then glyceraldehyde 3-phosphate gets turned into 1,3-bisphosphoglycerate, okay? Or we can go into acetyl-CoA if we have more steady, sustained energy needs. But if we need immediate energy, we'll continue to do glycolysis and fermentation. So what's different about the liver compared to the muscle?

Let's take a look. So the liver has actually two different enzymes that will trap glucose. It has hexokinase, which will trap glucose.

but hexokinase gets down regulated when you have a buildup of glucose 6 phosphate glucokinase okay so the liver uses this enzyme primarily to phosphorylate glucose in the liver why is that well the liver doesn't use a lot of glucose for metabolic energy the liver is generating very small amounts of atp because it doesn't need as much atp as say places like the muscle but you're doing a lot of atp usage So instead, hexokinase is usually down-regulated to the point of non-functionality in the liver, unless we're really low on blood glucose and it needs to take it in. And so since hexokinase isn't functioning, we still want to trap glucose in the liver. Why?

Because the liver is central to energy metabolism and storage. And so even though we're not trapping it to put it into glycolysis, we are trapping it so that we can use it for energy storage. So the Km of glucokinase is very high, okay, compared to hexokinase. So glucose has to be way more abundant for glucokinase to work.

So normally in the liver, we want to be sending out glucose. We are typically converting glucose 6-phosphate into glucose in the liver. so that we can send it to other parts of the body okay but if we are in extremely high glucose excess we still want to trap glucose in the liver so that we can convert it into glycogen so even though this has a very high km all that means is that it functions only at higher abundancy of glucose so brain and muscle have dibs on glucose before liver cells essentially Okay, what's different about phosphofructokinase in the liver?

Well, it's got the same regulatory mechanisms, but there's not usually a need for rapid APT production in the liver compared to the muscle. So another thing that is inhibited by is citrate in the liver. So citrate is an intermediate of the citric acid cycle, right? It's what gets made in the first step of the citric acid cycle and why it gets its name. And a buildup of citrate inhibits PFK function.

Why does citrate prevent PFK function? Okay, so citrate will prevent PFK function because a buildup of citrate implies that we have done enough glycolysis to make enough citrate for the liver's needs. And so we don't need to make any more PFK because the largest portion of pyruvate that gets made in the liver is gonna be converted into acetyl-CoA and ultimately become.

citrate in the citric acid cycle. So if we have too much citrate, we don't need to make any more. Okay, one other major difference in the liver is there is a second PFK enzyme.

So in the muscle, there's only a single PFK enzyme, and on the liver, we have two. And we'll consider the second one, PFK2, versus the first one is PFK1. So this PFK2 enzyme in the liver converts some fructose 6-phosphate into fructose 2,6-bisphosphate. Remember, PFK1 converts... F6P into F1 6P, PFK2 phosphorylates at a different site.

And so it becomes F2 6BP, that's fructose 2,6-bisphosphate. And this is a potent activator of PFK1. This might seem strange, okay, but let's think through why this might be true. So if we typically have fairly low and steady PFK activity in the liver, because we only want to make enough pyruvate, right, to meet very minor energy needs from that, and the primary function of glycolysis in the liver is going largely to be making acetyl-CoA to make citrate, okay?

Now we're at this low level of function, okay? However, every once in a while, we may need to activate glycolysis very quickly because we're at that low level. But let's say we deplete our citrate or we really do need some immediate ATP from glycolysis in the liver.

It does happen from time to time, right? So let's pretend Because we're in this low functioning state, right, we're normally high glucose level, glucokinase is functioning slowly compared to hexokinase. That means that phosphofructokinase is sort of at a low level of function. We typically are at high energy state. However, we can need to make more of any particular thing on short notice.

So PFK2 is an enzyme that can be active. reactivated to make this fructose 2,6-bisphosphate, which then hyperactivates PFK1. So it means that normally in the liver, glycolysis is at a very low level, but we have a switch that can quickly turn it on and hyperactivate it. Okay, why might we need that?

We can talk about that another time. Okay, pyruvate kinase finally differences in the liver. There's an isoform in the liver called...

L-form for liver form versus M-form in the muscle. What is the differences here? Well, same thing, ATP, high ATP allosterically inhibits this. Fructose 1,6-bisphosphate activates this, same thing.

This is also allosterically hindered by alanine. Why is that? Well, one of the major things, the reasons we do glycolysis in the liver isn't to generate a bunch of ATP typically, but it's to make things like pyruvate or citrate, et cetera. So if we've made enough pyruvate... right much of that pyruvate can get converted into alanine and when we've made enough alanine right then we don't need to go through and make more pyruvate and so since it's a simple conversion product of pyruvate this signals to shut off pyruvate production which down regulates pyruvate kinase okay so that is glycolysis and regulation of glycolysis now let's look at gluconeogenesis so gluconeogenesis synthesis of glucose from non-carbohydrate precursors.

Major site of gluconeogenesis is the liver, and we convert pyruvate to glucose in it. So all I've done here is I've gone, gluconeogenesis is basically just glycolysis in reverse, and I'll show you what I mean by that. It's not exact, but it's close.

So if we look at them side by side, and we start at pyruvate and gluconeogenesis on the left here, we see that our endpoint... for glycolysis is pyruvate we go in glycolysis we convert from phosphoenolpyruvate whereas pyruvate here the first step is to make oxaloacetate so this conversion of pyruvate to phosphoenolpyruvate is highly endergonic it's one of the most endergonic reactions that we have here in metabolism okay and so it's high energy input in order to make phosphoenolpyruvate from pyruvate. And in order to do it, we actually need an extra step. And so what we do is we use ATP. We not only use energy input from ATP and GTP, which is another nucleotide triphosphate that uses energy or can be used as an energy currency.

So not only do we input multiple phosphate breakage energies, but we also couple that with carboxylating. So adding a carbon dioxide to pyruvate, which we can then use in a second step to decarboxylate. Okay, why would we add a carbon dioxide and then remove a carbon dioxide in order to drive the reaction? Well, essentially, we're using the energy of entropy here. So we create a molecule that is higher energy by inputting ATP.

We couple that. increase in energy to also add a CO2. And when we convert that oxaloacetate into phosphoenolpyruvate and CO2, we have an increase in entropy. Okay, and if we are increasing entropy, that is another way to drive reactions. So decarboxylation reactions, because they increase entropy of the system, you go from one molecule to two molecules, okay, CO2 and phosphoenolpyruvate.

You can use that to drive reactions that would otherwise maybe just sort of barely happen energetically because you are driving entropy up. you can take small exergonic reactions and make them happen more easily. So the conversion of oxaloacetate to phosphenolpyruvate is not nearly as high energy need as the conversion of pyruvate to oxaloacetate, but coupling it with a GTP conversion to a GDP, as well as coupling it with a decarboxylation, means that it is just exergonic enough when it's coupled. that that change in entropy will drive it forward more spontaneously. Okay, so essentially the biggest differences here are that the conversion of pyruvate to phosphoenopyruvate, the reverse of the last reaction, needs a second step and needs an extra GTP input as well as needs to have a decarboxylation.

So instead of being pyruvate kinase, the reverse reaction from pyruvate to phosphoenopyruvate is two steps that requires two different enzymes. Now notice, all of the steps are the same, and all of them use the same enzymes. Because remember, enzymes increase the reaction rate of both the forward and the reverse reaction. So if we change the conditions to be favorable directionally, that enzyme will decrease the activation energy of both the forward and reverse reaction thereby increasing the rate of reaction in both directions and so all we need to do is change the conditions so a buildup of phosphoenolpyruvate will cause spontaneously the conversion by enolase into two phosphoglycerate we have phosphoglucomutase in both we have phosphoglycerate kinase in both okay instead of here we generate an atp we have to use an atp 1,3-bisphosphoglycerate is in both. That gets converted into glyceraldehyde 3-phosphate in both.

Okay. Glyceraldehyde 3-phosphate gets converted to fructose 1,6-bisphosphate in both. So essentially, you'll notice the differences only at the regulatory enzymes.

So remember, hexokinase, phosphofructokinase, or PFK. and pyruvate kinase were the key regulatory enzymes of glycolysis and those enzymes are not used in gluconeogenesis instead of pyruvate kinase we have pyruvate carboxylase and phosphoenol pyruvate carboxykinase so we have these two enzymes to substitute for the reverse reaction of pyruvate kinase and then all the reactions are the same just in reverse until we get to the analogous reverse reaction from pfk instead of pfk the reverse reaction from fructose 1 6 bisphosphate is catalyzed by fructose 1 6 bisphosphatase okay and once we get to hexokinase instead of hexokinase we have glucose 6 phosphatase which removes the phosphate from glucose 6 phosphate so gluconeogenesis glycolysis are reverse reciprocally regulated reactions these are the differences Just to review, analogous enzymes for the reverse reaction in each case. The regulatory enzymes for gluconeogenesis are the same steps as they are in glycolysis.

It's just the enzymes are different. So hexokinase is a regulated enzyme in glycolysis. The counterpart in gluconeogenesis, glucose 6-phosphatase, also one of the key regulatory enzymes.

PFK is analog, is fructose 1,6-bisphosphatase, and pyruvate kinase has these two enzymes in order to catalyze the two-step reaction. So if we look at this gluconeogenesis, this is just the same information only on the table that I've given you. So key irreversible step differences.

Pyruvate kinase, instead of pyruvate kinase, we have these two enzymes. These are the reactions they catalyze. PFK, it's analog is this, catalyzes this reaction. hexokinase instead we have glucose phosphatase catalyzes this so you should know this i just put it in a table you don't have to know the table that same information is here i just put it on a table for you okay all right so a little bit more information just to give details what is the conversion of pyruvate and oxaloacetate look like so we have pyruvate combined with co2 we use the conversion of atp to adp and a phosphate in order to drive the pyruvate carboxylase to form oxaloacetate okay so that energy input from atp allows us to add this carbon dioxide to pyruvate okay and then We can use GTP in order to add a phosphate, and we can use the decarboxylation in order to drive entropy.

So this very tiny exergonic reaction happens more readily because of the increase in entropy. We go from one molecule of oxaloacetate to one molecule of phosphoenolpyruvate and one CO2. So two different products here.

Or if you want to consider GTP, right, we have two molecules being broken into three molecules so higher entropy so pyruvate carboxylase okay so biotin is a covalently attached prosthetic group that serves as a carrier of activated co2 so we actually don't have just co2 we need an activated form of co2 which is carried by biotin co2 you don't have to memorize this this is just what's actually happening behind the scenes of this reaction and then also phosphoenol pyruvate co2 that was added to pyruvate by pyruvate carboxylase comes off on this step that's what drives this reaction forward through decarboxylation okay so these two reactions if you want to know sort of the net here okay so pyruvate plus atp plus gtp generates phosphoenol pyruvate and phosphate adp gdp as well as two hydrogens so how's gluconeogenesis powered in the cell well addition of phosphoryl groups to pyruvate is highly undergonic okay so If we wanted to add a phosphate group directly, which is basically what phosphoenolpyruvate is, right? Pyruvate plus this phosphate group. So if we wanted to add this directly, it would be 31 kilojoules per mole.

Formation of phosphoenolpyruvate from pyruvate is much less endergonic. It's 0.8 kilojoules per mole. And so because we have this very low... right we have we have to input energy right we have to input energy in the form of atp but instead we can drive this forward much more easily because that decarboxylation so decarboxylations often drive reactions that are otherwise highly endergonic so we'll learn a little bit more about this in the citric acid cyclin fatty acid synthesis we have a couple of other examples there okay and then the second reaction here fructose 1 6 bisphosphate is the second regulatory reaction here's more details of it We're just removing a phosphate from fructose 1,6-bisphosphate.

Okay. And so finally, what is the net here? Two pyruvates take two ATPs, two GTPs. You also use up to NADHs in order to form one glucose molecule, right?

So it's a lot of energy input, right? It costs more energy to make glucose than it does to break it down into pyruvate. And this would make sense. Otherwise, you'd have sort of a perpetual energy machine. because you could just use the energy from glucose to make more glucose and have energy left over.

So it must require more energy to build glucose from 2-pyruvates than you generate from glucose to make 2-pyruvates. So just like in glycolysis and gluconeogenesis, energetically unfavorable reactions are coupled with energetically favorable reactions. All of these conversions of ATPs to ADPs or GTPs to GDPs.

OK. in order to drive spontaneity of the process this is a very key thing okay so this slide represents the reciprocal regulation of these two things so gluconeogenesis is reciprocally regulated with glycolysis gluconeogenesis and glycolysis are coordinated so that within a cell one pathway is relatively inactive while the other one is highly active the basic premise of reciprocal regulation is that when glucose is abundant glycolysis will predominate when glucose is scarce gluconeogenesis will take over in a nutshell the things that up regulate glycolysis down regulate gluconeogenesis and the things that up regulate gluconeogenesis down regulate glycolysis let's take a look at it we have glucose and then on the left we have the key regulatory steps leading to formation of pyruvate hexakinase isn't in here hexakinase is somewhat up here but hexokinase is just about trapping glucose in the cells so we'll forget about it so these key regulatory steps this is why they're key regulatory steps the things that up and down regulate these cycles or these pathways are at these enzymes. So fructose 2,6-bisphosphate, we'll get into more detail here, but this molecule hyperactivates PFK. Remember, low energy state means that AMP binds to the allosteric binding side of PFK and prevents binding of ATP, so PFK can function better in low energy states.

So we have high energy, ATP allosterically downregulates PFK. Citrate buildup also downregulates PFK. pH will downregulate PFK.

So if we lower the pH, we'll downregulate PFK. And if we look at the reverse analogous enzyme in gluconeogenesis, okay, F2,6BP, while it will hyperactivate phosphofructokinase, it will deactivate fructose 1,6-bisphosphatase. Low energy means we downregulate gluconeogenesis.

If we are in a low energy state, we don't want to be using our energy to build glucose molecules within a cell. if we have a buildup of citrate, okay, we will activate gluconeogenesis. This is reciprocal regulation. What upregulates one, downregulates the other, and vice versa, okay?

And we see the same thing in pyruvate kinase and its analogs. Primarily, we see that high energy state downregulates pyruvate kinase and low energy state, okay, here. up regulate or sorry low energy state down regulates gluconeogenesis here also if we have a buildup of acetyl-CoA we want to use some of those carbons in order to generate glucose okay so a lot of what's happening with generating or turning glucose into pyruvate is that conversion of pyruvate and acetyl-CoA if we have too much acetyl-CoA we will say hey let's turn some of that pyruvate into glucose instead of making it into acetylcholine. So you should understand this slide pretty well.

Okay, so I talked about this reciprocal regulation. I used an example of in the liver, and I even talked about it on this slide, this fructose 2,6-bisphosphate. So what is fructose 2,6-bisphosphate?

So this is an interesting study, and you don't need to memorize this stuff about fructose 2,6-bisphosphate, other than it's a hyperactivator of PFK, and it downregulates. fructose 1 6 bisphosphatase so how does this work okay so let's pretend we are in a glucose abundant state in a glucose abundant state we would imagine we have build up a fructose 6 phosphate because if we're in an energy abundant state okay or a glucose abundant state then we are going to make our glucose into glucose 6 phosphate make our glucose 6 phosphate into fructose 6 phosphate right And so what does PFK do? If we are in a glucose abundant state, then it's going to convert some amount of our fructose 6-phosphate into fructose 2,6-bisphosphate, which will hyperactivate PFK1.

Okay, and what is doing that? PFK2 is using, is phosphorylating fructose 6-phosphate to make fructose 2,6-bisphosphate, which then hyperactivates PFK1 to convert fructose 6-phosphate into fructose 1,6-bisphosphate, right? That fructose 1,6-bisphosphate is that highest energy point in glycolysis, okay?

So if we have a buildup of glucose, we will want to take that glucose and push it through glycolysis. We do this in the liver, right, which is normally at a low level of glycolysis. Okay, we do this in the liver by making this hyperactivator through this other PFK enzyme.

which then says, hey, PFK1 activate, and let's turn that glucose into pyruvate. On the flip side, so the interesting thing about PFK2 is it has multiple different domains. It is a bifunctional kinase, so it's a kinase that uses ATP to add phosphate to fructose 6-phosphate. It also has a phosphatase domain, and when the kinase domain is active, the phosphatase domain is inactive.

And when the phosphatase domain is active, the kinase is inactive. If I just said that, essentially when one side is active, the other side is inactive. That is regulated through protein kinase A. We'll learn more about this when we get into gluconeogenesis.

Sorry, glycogenolysis and glycogenesis. We'll get more into protein kinase A. But what happens here? So glucagon stimulates pKa when blood glucose is scarce.

Okay. So PK is protein kinase A. So signaling when blood glucose is scarce. activates protein kinase A. If blood glucose is scarce, FBPase 2 is very active, which means PFK2 is very inactive.

If we don't have much glucose, we turn this switch so that BBPase 2 is active. That's the phosphatase domain. Glycolysis gets inhibited and gluconeogenesis gets stimulated. In this case, where we have low blood glucose, glucose is scarce.

we activate fbps2 we inhibit glycolysis and we make more glucose now you might be thinking wait a minute if glucose is scarce and we don't have much glucose why would we want to be using our energy to make glucose remember this is happening in the liver the liver doesn't need much glucose to make energy and low glucose in the liver means it needs to make glucose to transport to tissues that do need it to make energy. So when the liver has low glucose, it makes more glucose. This is counterintuitive because if you think about it in the muscle, when the muscle is at low glucose, it needs to make sure that it is making more energy. And so it needs to activate different things.

So if we are at low glucose levels, we need to make glucose. Okay. And we do that by converting the fructose 2,6-bisphosphate. back into fructose 6-phosphate. We convert it back into fructose 6-phosphate, we can convert that fructose 6-phosphate into glucose 6-phosphate, turn the glucose 6-phosphate into glucose.

It also, right, directly removes this hyperactivator of PFK. It converts it into normal fructose 6-phosphate. Then, okay, if we have high levels of fructose 6-phosphate, we stimulate another phosphatase that dephosphorylates PFK2. thereby inactivating the fbpase activity and activating the kinase activity so we can convert fructose 6-phosphate into fructose 2 6-bisphosphate and hyperactivate glycolysis so this essentially creates a simple switch related to do we have low glucose or do we have high fructose 6-phosphate remember if we have low glucose right then that will mean that we we'll convert our glucose 6 into glucose we will have less fructose 6-phosphate if we have high glucose we will naturally turn our glucose into glucose 6-phosphate turn our glucose 6-phosphate into fructose 6-phosphate so fructose 6-phosphate concentration is a direct correlation to glucose levels and that's why high levels of this will turn on glycolysis and low levels of glucose will turn on or sorry we'll turn sorry High levels of fructose 6-phosphate will turn on glycolysis, and low levels of glucose will turn on gluconeogenesis in the liver. It creates this switch between these two forms that we can have.

Okay, so that is reciprocal regulation, right? This slide right here, this is an example of how things happen differently in the liver. And then we can look at sort of whole body differences and how rather than just reciprocal regulation, things work in concert.

So that you can be doing... reciprocally regulated pathways at the same time where they are needed and how does that work okay so if we look in contracting skeletal muscle we have the formation of lactate muscles are working hard they're converting their glucose into pyruvate to generate energy they are using that pyruvate to make lactate to regenerate nad plus so they can use more glucose to generate more pyruvate etc lack can be transported in the blood to the liver where it can be converted back into pyruvate and pyruvate can be converted into glucose in order to send glucose to the muscle and that's the cycle okay so the liver restores the level of glucose necessary for active muscle cells which derive ATP from the glycolytic conversion of glucose to lactate so you do do gluconeogenesis in the liver simultaneously when you're doing glycolysis in the muscle reciprocal regulation okay but at the same time except in different compartments okay so it's good to understand this idea okay and this is a i think brainstorm and share activity that we have i don't have any test your knowledge questions for this chapter specifically um one suggestion that i would make is to uh fill in the glycolysis chart, which I may provide for you on Canvas. And that will end the lecture.

Transcript for:Glycolysis and Gluconeogenesis Overview

Transcript for:
Glycolysis and Gluconeogenesis Overview