Pentose Phosphate Pathway

oh my goodness biochemist we are finally here at the last concept from chapter 12 and we're going to be looking at the pentos pentos phosphate pathway you'll see it often abbreviated as p p p pentos phosphate pathway so let's to take a look at what this pathway is so when we're looking at this figure from the beginning of the chapter we saw that polysaccharides can be broken down into monosaccharides and those monosaccharides uh can be converted into glucose now these monosaccharides can also be converted into nucleotides and that's one of the main things that the pentos phosphate pathway is going to do now there are other things that it does but that is just one of the things that it does is it can convert our monosaccharide specifically glucose 6 phosphate into nucleotides let's look at how we accomplish this okay so first this pathway takes place entirely within the cytoplasm so there's no exporting or importing of any for this pathway it is um not in any organel it's specifically in the cytoplasm and what it what its main function is even though it is going to be helping making nucleotides its main function is actually to make NAD pH so nicotinamide adenine dinucleotide phosphate why nadph is important is it is the main reducing agent of the cell so when we have um done lots of reduction reactions and we don't have any NAD pH the pentos phosphate pathway is how we regenerate our nadph okay so that is one of its most important functions another important um function for this is that it's going to be making ribos 5 phosphate from glucose and so ribos 5 phosphate is the ribos sugar that is going to make help us make DNA and RNA polymers now we haven't talked about DNA and RNA yet um but this is how we're going to make the ribos Spy phosphate which we'll be able to make the DNA and the RNA okay so again some important questions so what does this path pathway accomplish for us it generates nadph and it does that in what's called its oxidative phase and then it's non oxidative phase it's going to help us generate our ribos 5 phosphate and it can also help us regenerate glucose 6 phosphate depending on the needs of the cell and we'll go through how the needs of the cell affect what the pentos fat phosphate pathway does our net reaction we're going to take six glucose 12 nadp uh pluses so this is the um the the oxidized form of nadph sorry uh and some Waters and we're going to turn them into five glucoses so we're going from six glucoses to five glucoses we're going to get 12 nadph so we're going to get quite a bit of our reducing agent from this some hydrogen ions and some carbon dioxide gas our main enzymes uh the main one we're going to be looking at is this glucose 6 phosphate dehydrogenase so this is the committed step in our pathway so that means because it's committed it's going to be um highly regulated and it's going to be regulated by the product nadph so if we have enough nadph this enzyme won't go um so we don't need to commit our glucose 6 phosphate to this dehydrogenase reaction if we already have enough reducing in the cell our other enzymes are these transketolases and trans aldolases and we're not going to look specifically at any any one enzyme but what they're going to do is called a carbon Shuffle which means we're just going to be moving carbons around in our sugars to get to useful carbon molecules all right we've got these two phases the oxidative phase and the nonoxidative phase in our oxidative phase overall what we're going to be doing is taking this glucose 6 phosphate and turning it into to ribulose 5 phosphat and will generate carbon dioxide and two NAD PHS so those two nadp pluses will become two NAD PHS now if we think back to this balanced reaction we had six glucoses here and we're going getting these 12 NAD PHS and six carbon dioxides so this is just one molecule so this needs to happen six times for our overall reaction so this is again our oxid state of phase we're um going to be oxidizing glucose to ribulose um and generating this oxidized form of carbon uh carbon dioxide and at the same time reducing nadp plus to nadph and this nadph can then go on to other biosynthetic Pathways to be a wonderful reducing agent for the cell all right our non oxidative phase now beware it's going to get a little crazy is all of this so our non oxidated phase we can do all of this that you see in the middle here this is all the carbon Shuffle that I was talking about so we're taking that RI ribulose 5 phosphate and converting it into ribos fructose uh glycer alide phosphate glucose 6 phosphate and going through a lot of different intermediates in order to do this and from that that ribos 5 phosphate we can use to make nucleotides that glucose 6 phosphate we can use to go through glycolysis so we can generate these other very useful molecules um but the main part of the pendos phosphate pathway is just this first part this going from glucose to ribulose um because that is going to be generating our NAD PHS which is kind of the important part for the cell all right so let's look at that oxidative phase there are three key enzymes but the one that is our committed step is this first enzyme so what we can see is we've got our glucose 6 phosphate uh we're going to use this glucose 6 phosphate dehydrogenase and we are going to oxidize it so we're taking it from an alcohol this case actually a hem acetal into this Ester so um technically this would be a lactone because we're in the ring so this lactone here um it is only used by the pentus phosphate pathway so that is why this is the committed step because this um glucola glucono lactone has no other metabolic fate aside from to be converted into the six phosphogluconate so its only fate is the pentos phosphate pathway so we've oxidized this um Esther or lactone and then we are going to hydrolize the Esther bond to give us this carboxilic acid technically it's a carboxilate because it's deprotonated so we're in our open chain form but this is making it Prime for this carbon dioxide so here's the carbon and the oxygen here this carbon dioxide to leave as um this carbon dioxide gas and now we've removed a carbon so we had six carbons and now we have only five carbons in our carbon chain so this would be our ribulose 5 phosphate and in the process because we've done two oxidation reactions we're going to be generating two NAD ph's so one here and one here so this nadp+ is our oxidizing agent because it is allowing our glucose 6 phosphate and our six phosph gluconate to be oxidized to carbon dioxide and this lactone all right so this is our carbon Shuffle so this is our nonoxidative phase so we've got 1 2 3 4 5 six glucose 6 phosphates here and we are going to go through these carbon shuffles so you can see this um six phosphate going to this uh C5 C5 means it's a carbon chain of five so this is our ribus phosphate that was our our product in our last reaction so that's going to happen six times so we're going to get these six C5 intermediates we're going to um make two molecules of nadph and release carbon dioxide for every glucose 6 phosphate that goes to the C5 intermediate these two c5s are going to recombine to give us a C3 and a C7 now they can then Shuffle their carbons to give us fructose 6 phosphat um and then the C4 molecule and you can see we've just got this series of of um our carbons shuffling around from molecule to molecule but we've got some very key intermediates here fructose 6 phosphate glycer alide phosphate glucose 6 phosphate here and these can all enter into our glycolysis cycle which is why this is included in this chapter is that all of these molecules are intermediates for glycolysis all right the six glucoses that we start with get converted into five glucoses hopefully you're thinking to yourself where does those other six carbons go like we had six glucose six phosphates and now we only have five where did the six carbons from that other glucose go and it became carbon dioxide so there are six molecules of carbon dioxide here and that is what has happened to them is they have just all the carbons have been oxidized the equivalent of one glucose 6 phosphate for every six you started with okay so there is a lot of flux through this pendos phosphate pathway but it is tightly regulated and what it does depends on what the cell needs so if your goal is to make more nadph then what you're going to do is when you get that glucose 6 phosphate at the end of your non- oxidative phase you're going to take that glucose 6 phosphate and you're going to put it back into the pentos phosphate Pathway to generate more nadph so that will be the fate of your glucose is it just goes back in and makes some more of this nadph so that will be that will be the path that we will go if we have low nadph now if we need to replenish nucleotides then we're not actually going to generate glucose 6 phosphate we're going to stop at this ribos 5 phosphate and then we're going to use that to make more nucleotides so this ribos 5 phosphate will be shuttled off to make nucleotides if that's what we need now if the cell is low on ATP if we don't have a lot of ATP our energy levels are low then once we generate um this glucose 6 phosphate instead of putting it back into the pentos phosphate pathway we're going to take it and we're going to put it through glycolysis and get ATP out of it so that is the beautiful thing about this pathway is that it can be modulated to what you need and so the cell can focus on making the the things that it needs in order to be successful so again our goal is regenerating this nadph we can make more nadph by just putting the glucose 6 phosphate back into the pathway if we need nucleotides we can use this ribos 5 phosphate to make us more nucleotides and if we need more energy we can just take the product that glucose 6 phosphate and go through glycolysis all right so the regulation of this is going to occur based on our nadp H and our nadp+ levels so if we have high levels of this nadp+ that means we need more nadph in that case we're going to activate this glucose 6 phosphate dehydrogenase and our glucose 6 phosphate instead of going through glycolysis it will go through the pentos phosphate Pathway to generate that nadph now if we have high levels of nadph that is going to inhibit our glucose 6 phosphate dehy hydrogenates and that is going to shift us from the pintos phosphate pathway into glycolysis so it will shut down the pentos phosphate pathway and encourage our glucose 6 phosphate to go through glycolysis because we have a lot of nadph so let's go make some ATP instead but if we have low nadph levels which means High nadp plus levels then we want to generate more nadph before we go through and go through glycolysis

oh my goodness biochemist we are finally here at the last concept from chapter 12 and we&#39;re going to be looking at the pentos pentos phosphate pathway you&#39;ll see it often abbreviated as p p p pentos phosphate pathway so let&#39;s to take a look at what this pathway is so when we&#39;re looking at this figure from the beginning of the chapter we saw that polysaccharides can be broken down into monosaccharides and those monosaccharides uh can be converted into glucose now these monosaccharides can also be converted into nucleotides and that&#39;s one of the main things that the pentos phosphate pathway is going to do now there are other things that it does but that is just one of the things that it does is it can convert our monosaccharide specifically glucose 6 phosphate into nucleotides let&#39;s look at how we accomplish this okay so first this pathway takes place entirely within the cytoplasm so there&#39;s no exporting or importing of any for this pathway it is um not in any organel it&#39;s specifically in the cytoplasm and what it what its main function is even though it is going to be helping making nucleotides its main function is actually to make NAD pH so nicotinamide adenine dinucleotide phosphate why nadph is important is it is the main reducing agent of the cell so when we have um done lots of reduction reactions and we don&#39;t have any NAD pH the pentos phosphate pathway is how we regenerate our nadph okay so that is one of its most important functions another important um function for this is that it&#39;s going to be making ribos 5 phosphate from glucose and so ribos 5 phosphate is the ribos sugar that is going to make help us make DNA and RNA polymers now we haven&#39;t talked about DNA and RNA yet um but this is how we&#39;re going to make the ribos Spy phosphate which we&#39;ll be able to make the DNA and the RNA okay so again some important questions so what does this path pathway accomplish for us it generates nadph and it does that in what&#39;s called its oxidative phase and then it&#39;s non oxidative phase it&#39;s going to help us generate our ribos 5 phosphate and it can also help us regenerate glucose 6 phosphate depending on the needs of the cell and we&#39;ll go through how the needs of the cell affect what the pentos fat phosphate pathway does our net reaction we&#39;re going to take six glucose 12 nadp uh pluses so this is the um the the oxidized form of nadph sorry uh and some Waters and we&#39;re going to turn them into five glucoses so we&#39;re going from six glucoses to five glucoses we&#39;re going to get 12 nadph so we&#39;re going to get quite a bit of our reducing agent from this some hydrogen ions and some carbon dioxide gas our main enzymes uh the main one we&#39;re going to be looking at is this glucose 6 phosphate dehydrogenase so this is the committed step in our pathway so that means because it&#39;s committed it&#39;s going to be um highly regulated and it&#39;s going to be regulated by the product nadph so if we have enough nadph this enzyme won&#39;t go um so we don&#39;t need to commit our glucose 6 phosphate to this dehydrogenase reaction if we already have enough reducing in the cell our other enzymes are these transketolases and trans aldolases and we&#39;re not going to look specifically at any any one enzyme but what they&#39;re going to do is called a carbon Shuffle which means we&#39;re just going to be moving carbons around in our sugars to get to useful carbon molecules all right we&#39;ve got these two phases the oxidative phase and the nonoxidative phase in our oxidative phase overall what we&#39;re going to be doing is taking this glucose 6 phosphate and turning it into to ribulose 5 phosphat and will generate carbon dioxide and two NAD PHS so those two nadp pluses will become two NAD PHS now if we think back to this balanced reaction we had six glucoses here and we&#39;re going getting these 12 NAD PHS and six carbon dioxides so this is just one molecule so this needs to happen six times for our overall reaction so this is again our oxid state of phase we&#39;re um going to be oxidizing glucose to ribulose um and generating this oxidized form of carbon uh carbon dioxide and at the same time reducing nadp plus to nadph and this nadph can then go on to other biosynthetic Pathways to be a wonderful reducing agent for the cell all right our non oxidative phase now beware it&#39;s going to get a little crazy is all of this so our non oxidated phase we can do all of this that you see in the middle here this is all the carbon Shuffle that I was talking about so we&#39;re taking that RI ribulose 5 phosphate and converting it into ribos fructose uh glycer alide phosphate glucose 6 phosphate and going through a lot of different intermediates in order to do this and from that that ribos 5 phosphate we can use to make nucleotides that glucose 6 phosphate we can use to go through glycolysis so we can generate these other very useful molecules um but the main part of the pendos phosphate pathway is just this first part this going from glucose to ribulose um because that is going to be generating our NAD PHS which is kind of the important part for the cell all right so let&#39;s look at that oxidative phase there are three key enzymes but the one that is our committed step is this first enzyme so what we can see is we&#39;ve got our glucose 6 phosphate uh we&#39;re going to use this glucose 6 phosphate dehydrogenase and we are going to oxidize it so we&#39;re taking it from an alcohol this case actually a hem acetal into this Ester so um technically this would be a lactone because we&#39;re in the ring so this lactone here um it is only used by the pentus phosphate pathway so that is why this is the committed step because this um glucola glucono lactone has no other metabolic fate aside from to be converted into the six phosphogluconate so its only fate is the pentos phosphate pathway so we&#39;ve oxidized this um Esther or lactone and then we are going to hydrolize the Esther bond to give us this carboxilic acid technically it&#39;s a carboxilate because it&#39;s deprotonated so we&#39;re in our open chain form but this is making it Prime for this carbon dioxide so here&#39;s the carbon and the oxygen here this carbon dioxide to leave as um this carbon dioxide gas and now we&#39;ve removed a carbon so we had six carbons and now we have only five carbons in our carbon chain so this would be our ribulose 5 phosphate and in the process because we&#39;ve done two oxidation reactions we&#39;re going to be generating two NAD ph&#39;s so one here and one here so this nadp+ is our oxidizing agent because it is allowing our glucose 6 phosphate and our six phosph gluconate to be oxidized to carbon dioxide and this lactone all right so this is our carbon Shuffle so this is our nonoxidative phase so we&#39;ve got 1 2 3 4 5 six glucose 6 phosphates here and we are going to go through these carbon shuffles so you can see this um six phosphate going to this uh C5 C5 means it&#39;s a carbon chain of five so this is our ribus phosphate that was our our product in our last reaction so that&#39;s going to happen six times so we&#39;re going to get these six C5 intermediates we&#39;re going to um make two molecules of nadph and release carbon dioxide for every glucose 6 phosphate that goes to the C5 intermediate these two c5s are going to recombine to give us a C3 and a C7 now they can then Shuffle their carbons to give us fructose 6 phosphat um and then the C4 molecule and you can see we&#39;ve just got this series of of um our carbons shuffling around from molecule to molecule but we&#39;ve got some very key intermediates here fructose 6 phosphate glycer alide phosphate glucose 6 phosphate here and these can all enter into our glycolysis cycle which is why this is included in this chapter is that all of these molecules are intermediates for glycolysis all right the six glucoses that we start with get converted into five glucoses hopefully you&#39;re thinking to yourself where does those other six carbons go like we had six glucose six phosphates and now we only have five where did the six carbons from that other glucose go and it became carbon dioxide so there are six molecules of carbon dioxide here and that is what has happened to them is they have just all the carbons have been oxidized the equivalent of one glucose 6 phosphate for every six you started with okay so there is a lot of flux through this pendos phosphate pathway but it is tightly regulated and what it does depends on what the cell needs so if your goal is to make more nadph then what you&#39;re going to do is when you get that glucose 6 phosphate at the end of your non- oxidative phase you&#39;re going to take that glucose 6 phosphate and you&#39;re going to put it back into the pentos phosphate Pathway to generate more nadph so that will be the fate of your glucose is it just goes back in and makes some more of this nadph so that will be that will be the path that we will go if we have low nadph now if we need to replenish nucleotides then we&#39;re not actually going to generate glucose 6 phosphate we&#39;re going to stop at this ribos 5 phosphate and then we&#39;re going to use that to make more nucleotides so this ribos 5 phosphate will be shuttled off to make nucleotides if that&#39;s what we need now if the cell is low on ATP if we don&#39;t have a lot of ATP our energy levels are low then once we generate um this glucose 6 phosphate instead of putting it back into the pentos phosphate pathway we&#39;re going to take it and we&#39;re going to put it through glycolysis and get ATP out of it so that is the beautiful thing about this pathway is that it can be modulated to what you need and so the cell can focus on making the the things that it needs in order to be successful so again our goal is regenerating this nadph we can make more nadph by just putting the glucose 6 phosphate back into the pathway if we need nucleotides we can use this ribos 5 phosphate to make us more nucleotides and if we need more energy we can just take the product that glucose 6 phosphate and go through glycolysis all right so the regulation of this is going to occur based on our nadp H and our nadp+ levels so if we have high levels of this nadp+ that means we need more nadph in that case we&#39;re going to activate this glucose 6 phosphate dehydrogenase and our glucose 6 phosphate instead of going through glycolysis it will go through the pentos phosphate Pathway to generate that nadph now if we have high levels of nadph that is going to inhibit our glucose 6 phosphate dehy hydrogenates and that is going to shift us from the pintos phosphate pathway into glycolysis so it will shut down the pentos phosphate pathway and encourage our glucose 6 phosphate to go through glycolysis because we have a lot of nadph so let&#39;s go make some ATP instead but if we have low nadph levels which means High nadp plus levels then we want to generate more nadph before we go through and go through glycolysis

Transcript for:Pentose Phosphate Pathway

Transcript for:
Pentose Phosphate Pathway