the pentose phosphate pathway consists of two different phases we have the oxidative and the non oxidative phase now previously we focused on the oxidative phase and we saw that in the oxidative phase the cells of our body transform a single glucose 6-phosphate molecule into two NADPH molecules and one ribose 5-phosphate sugar molecule now what do our cells use these two different molecules for so as we discussed previously the NADPH molecules are very important reducing agents that exist inside our cells because the cells actually use these molecules to help generate many other biological molecules so things like fatty acid molecules cholesterol molecules nucleotide molecules neurotransmitters all these things require NADPH molecules in addition the cells also use the NADPH molecules to help detoxify many different types of toxic agents that exist inside ourselves now what about the ribose 5-phosphate molecule well the cells of that of our body use the ribose 5-phosphate to help generate nucleotide based biological molecules so any type tomate anytime the molecule contains a nucleotide that means it requires ribose 5-phosphate so things like nucleic acid so DNA and RNA ATP molecules nadh molecules fa d molecules as well as coenzyme a molecules all these different things require ribose 5-phosphate now as it turns out the majority of the cells of our body most of the time actually require the NADPH much more than they need the ribose 5-phosphate molecule and so what our cells actually do is they take the ribose 5-phosphate that is produced via the oxidative phase and they transform that into glycolytic intermediates why well because these glycolytic intermediates can now be transformed into glucose 6-phosphate molecules and these glucose 6-phosphate can undergo the oxidative phase to produce even more NADPH molecules and it turns out that this process here the transformation of the ribose 5-phosphate into these glycolytic intermediates is the non oxidative phase of the pentose phosphate pathway so once again when the cells need NADPH much more than ribose 5-phosphate molecules the cells can actually transform this pentose sugar the ribose 5-phosphate into specific like oolitic intermediates via the non oxidative phase so we have the oxidative phase and the non oxidative phase and this constitutes the pentose phosphate pathway now the non oxidative phase of the pentose phosphate pathway can be broken down into four processes so we have process one process to process three and process 4 so let's begin by focusing on process one now in process one we actually have two steps in the first step we want to take the ribose 5-phosphate molecule and transform it into an isomer version rib ulos by phosphate and this is actually the same reaction that we discussed in the previous lecture except a ch3 it's in Reverse and so we have the same enzyme as we discussed previously phosphor Pancho's isomerase that catalyzes this reaction now once we form the RHIB ulos 5 phosphate it then undergoes a second reaction which is catalyzed by phosphate pentose ephemeris and so what this does is it transforms the rig below 5 phosphate into the cellulose fiber State and the only difference between these two molecules is the stereochemistry of the third carbon so this carbon here in this carbon here they have a different stereochemistry now why do we need this specific stereochemistry why can we use this well because the enzyme in the second process of this pathway basically uses only this type of stereochemistry and not this type of stereochemistry so we need to form the cellulose as a result of this trans catalase that we'll talk about in just a moment so ultimately in process one we want to transform rival ribose 5-phosphate into as allele O's by phosphate and notice we begin with two of them so you have two of these intermediates and we form two of these za you Lowe's 5 phosphate products now one of these xylose molecules is used in step 2 and the other one is used in step 4 as we'll see in just a moment so let's move on to step number process 2 of the pentose phosphate pathway specifically the non oxidative phase of this pathway so we take one of these cellulose 5-phosphate molecules and we take another ribose 5-phosphate molecules so so far we actually used three ribose 5-phosphate so two were used here and now the third one we're using in this particular step so we have the enzyme trans catalase which actually requires a cofactor we call thiamine pyrophosphate and we'll talk about the mechanism of this enzyme and what this actually does in the next lecture but basically what the trans catalase actually does it takes a two carbon group from the cellulose it takes this entire section places it onto the ribose so notice both of these are pentose sugars five carbon sugars and when we transfer this section onto this molecule we basically form we extend that sugar by two carbons and we form a seven carbon sugar known as cito have to Lowe's seven phosphates now if we take away these two carbons from the cellulose we essentially form a trials a three carbon sugar and that three carbon sugar is known as glyceraldehyde 3-phosphate so the products of step 2 reaction to of this particular oxidative phase is the seat will have two lows seven phosphate and the glyceraldehyde 3-phosphate and is catalyzed by the trans key to lace now in process three of the of the non oxidative phase we now take these two products and these two products will act as reactants in process three now the enzyme in this particular case will be different the enzyme here is trans aldolase and what trans aldolase does is it takes this entire three carbon section here and transfers it onto this carbon here and so we transform this molecule into URI throws four phosphate so we take off three carbons and so this is a four carbon sugar and then we place the three carbons onto this molecule so we form a six carbon sugar the fructose 6 phosphate and this fructose 6-phosphate is one of these glycolytic intermediate products so this is actually the final product or one of the final products in the non oxidative phase now what we want to do in the final step in the final process is we want to take the wreath rose four phosphate produced in process three and we want to take the second xylose by phosphate that we still have left over from process one remember we only use one of the two cellulose molecules that we produced in step one and process one so we use this one right here and now we use the second one in this process for now the enzyme that catalyzes the process for is the same enzyme that we used here and so it's no surprise that this same enzyme uses the same substrate molecule and what it does is just like in this case it took off this two carbon component from the cellulose and place it onto the ribose in this case and once a again takes off this two carbon component and places it onto this sugar molecule here and so we extend this four carbon sugar by two and we form a six carbon sugar we call fructose 6-phosphate which is once again a glycolytic intermediate molecule and when we cut this one by two carbons we form the 3 carbon triose molecule known as gap the glyceraldehyde 3-phosphate and remember that gap glyceraldehyde 3-phosphate is also a glycolytic intermediate so we see that if we sum up all these four processes this is the net reaction that we actually get so we have the input 3 ribose buzz 3 ribose 5-phosphate molecules so 2 in this step 2 in this process and 1 in this process and we essentially get back to fructose 6-phosphate molecules and a single glyceraldehyde 3-phosphate and so now these are the glycolytic intermediates that can be transformed into glucose 6-phosphate and that glucose 6-phosphate can undergo the oxidative phase to form even more NADPH molecule so when the cell actually means the NADPH much more than it actually needs the ribose 5-phosphate we undergo the non oxidative phase of the pentose phosphate pathway to help us generate even more of these NADPH molecules on top of that what the non oxidative phase of the pentose phosphate pathway allows us to do is it allows us to actually ingest ribose sugars into our body because via this particular pathway we can actually break down the ribose sugar into glycolytic instruments and then those intermediates can be used via glycolysis to actually generate high energy ATP molecules so we see that the link between glycolysis and the pentose phosphate pathway is the non oxidative days of the pentose phosphate pathway