so this chapter talks about glycolysis and in this chapter we're going to talk about how ATP is generated in this bike elliptic pathway and it will talk about some steps that are non spontaneous spontaneous some steps and also how these reaction steps are regulated so almost all or all types of organisms use glucose okay and it's very important fuel in all life forms so what what are the reasons why glucose is such a important fuel as I mentioned before our red blood cells can only use glucose okay and even for brain if your nones not starving or not fasting so your brain primarily use glucose so these are the reasons first is that glucose may have been available fuel source okay for primitive biochemical systems okay and second is that glucose is one of the most stable hexoses and it has a low tendency to non enzymatically glycosylated proteins so why is this reason for or why glucose is a primitive or prebiotic fuel source so for if you have a protein that is glycosylated most of the time okay most of the time the protein cannot function properly if it is glycosylated but of course we already discuss about glycosylated protein such as the glycoprotein erythropoietin which is a hormone that stimulates the production of red blood cells in that case the like oscillation is very important because it actually stabilized the structure of the protein are at a point in okay but if you have a protein that is glycosylated sometimes the protein or the enzyme is not going to be effective in terms of exerting it some activity the stability of the glucose lies on the fact that glucose molecule experienced the least amount of steric strain okay being a six membered ring and also most all these hydroxyl groups are in the equatorial position if you remember the beta anomer off of glucose so when they are in the equatorial position and the molecule glucose is very stable so what are the end products of the glycolysis pathway so if you start with one molecule of glucose and we know that one one a BlueCross molecule has six carbons right so when glucose undergoes glycolysis it will ultimately produce two molecules of pyruvate okay or pyruvic acid but nope arabic acid loses its proton at physiological conditions so it becomes pyruvate molecule and then he also produced two ATP molecules and two NADH molecules and we know from our previous discussion that NADH is your activated electron carrier okay and pyruvate is a three carbon molecule so the calluses can be divided into two stages the energy investing stage and the energy producing stage so keep in mind that the ultimate goal of all these pathways metabolic pathways is to burn or to oxidize the fuels such as glucose to produce ATP right so you will notice that in glycolysis before you can make ATP you need to sacrifice the cells your cells need to sacrifice some ATP it will use some ATP in order to produce more ATP so it's like you need to invest first okay before you make profit you need to make sacrifices first before you can you can get what you want all right so here's the energy investing stage or stage one and so you can see it involves one two three four and then five steps alright so each of these steps is I'm catalyzed by a certain class of enzymes okay and remember from our previous from the previous chapters that we have a total of six different classes of enzymes so we will will analyze these steps each steps okay in terms of the reaction involved and the enzyme involved in catalyzing these reactions so for the first step of the reaction glucose okay it's converted to glucose 6-phosphate so what does it mean glucose a phosphate group is added to carbon six okay so if you have a group added to carbon six and the source of your phosphate is your ATP so in this case you'll see in this step ATP provides the phosphate okay to glucose to make glucose 6-phosphate so this reaction is catalyzed by a class of enzyme called a transferase okay because the phosphate is transferred from ATP to glucose to make glucose 6-phosphate the second step is glucose 6-phosphate turns into fructose 6-phosphate okay so what class what class of enzyme is responsible for that conversion so glucose 6-phosphate to fructose 6-phosphate remember glucose has six carbons fructose also has six carbons in the phosphate position did not change right but glucose turns to fructose and what is the relationship between these two these are isomers so therefore this step is catalyzed by an isomerase okay and then after fructose 6-phosphate is formed then the third step is converting photo 6-phosphate to fructose 1 6 bisphosphate so take note of the name bisphosphate and not diphosphate when you see you when you use the word diphosphate the phosphate the thought that two phosphate groups are covalently bound to one another just like adp okay i don't seem dye phosphate but this is this phosphate so meaning there are two phosphate groups okay attached to the fructose molecules one on carbon 1 and the second on carbon 6 so what kind of react or what kind of enzyme catalyzed catalyzes this reaction so again to add the other phosphate on carbon 1 ok you need ATP again that's the source of your phosphate and therefore the ATP transfers its phosphate to fructose 6-phosphate to form the fructose 1 6 bisphosphate it is also catalyzed by a transferase enzyme so as you can see stage 1 is we are investing energy meaning we are using ATP so that burning up glucose okay on the downstream pathway would make a lot of ATP molecules so we are investing two ATP on this stage alright so next step is the conversion of fructose 1 6 bisphosphate into the glyceraldehyde-3-phosphate and dihydroxyacetone phosphate so notice that the arrow is actually split into two so meaning at this stage the fructose 6 1 6 bisphosphate is split into two 3-carbon molecules two carbon three carbon molecules remember that we are all dehyde is the simplest aldose in nature and this has three carbons dihydroxyacetone is also the simplest sugar the simplest ketose which also has 3 carbon 3 carbons in this molecule they are just phosphorylated alright so what type of enzyme catalyzes this this cleaving of a big molecule into two and you can see that there's no water in gold if there is a cleaving of bond so bond cleavage with the involvement of water if you use water molecules so that means that enzymes is going to be called a hydrolase but you don't see any enzyme I mean you don't see any water molecules therefore this reaction splitting the big molecule into two smaller molecules is catalyzing catalyzed by lyase ok so lies if you remembered our definition from I think from chapter 6 lyase is essentially catalyzing reactions involving the formation are the formation of a double bond or addition to a double bond but that is actually most most often accompanied by cleavage of cleaving your buns so you can cleave carbon-carbon single bond carbon single carbon oxygen single bond carbon sulfur single bond or carbon nitrogen single bond or other types of bonds okay so these bonds will be cleaved without the addition of water molecule all right so because when most most are most often when these bonds are cleaved it is accompanied by their company by the formation of a double bond okay so that's your lies and then step 5 right here dihydroxyacetone phosphate to glyceraldehyde 3 phosphate so what is this reaction involved so notice that glyceraldehyde 3-phosphate is your simplest aldose okay simplest aldose sugar which can which consists of 3 carbons dihydroxyacetone is your simplest ketose sugar also 3 carbon so if you if you revisit their structures they have the same the same number of everything same number of carbons hydrogen's and oxygens so that means these two are isomers right constitutional isomers so for step 5 since they have two hydroxy acid on phosphate turns into glyceraldehyde-3-phosphate you see that they are exactly the same means step five involved they use our an isomerase enzyme as well okay and you might wonder why dihydroxyacetone phosphate needs to be converted into glyceraldehyde 3-phosphate so the reason is that an in stage two when you go to stage two only gristle the high 3 phosphate can enter stage 2 okay which is the second half of glycolysis so in order for for the rest of the glucose carbon to enter stage 2 the hydroxy acid and phosphate must be converted into glyceraldehyde-3-phosphate so that nothing is wasted and you notice that now in stage 2 it's run in duplicate right because now you got less roba hydrate phosphate and glyceraldehyde-3-phosphate so just this times two so that's your stage two which is your energy producing step or stage okay so and this in this stage you have [Music] so this is 6 7 8 9 and 10 so that's the rest of the black odd glycolytic steps so from glyceraldehyde 3-phosphate it turns into glycerate 1 3 bisphosphoglycerate d+ and you produce NADH okay so take note that here nad Plus this is the oxidized form of your nicotinamide adenine dinucleotide and when it accepts remembered it always accepts two electrons it forms the reduced form okay so reduce so now that molecule carries two electrons so that's is your activated electron carrier so and you also need to add inorganic phosphate for this conversion okay but the main point here is that since this step involves that electron carrier NADH so automatically this step is catalyzed by an optional reductase okay because you see there's a transfer electrons so that is your redox reaction so at this point you see that now you produce the glycerate 1 3 bisphosphoglycerate be P G this is 1 3 bisphosphoglycerate which is one of the high energy molecules that is produced in glycolysis in fact this has higher phosphoryl transfer potential than ATP okay so therefore this has this will likely donate its phosphoryl groups because it's a high-energy molecule to adp to form ATP in a so you can see for the seconds for the next step step 7 now adp okay reacting with the 1 3 BP g ok converts itself into ATP so now you produce an ATP molecule on this stage and also glycerate 3 phosphate so notice the name the name changed glyph l'm from glycerate 1 3 bisphosphoglycerate groups one in carbon one and one in carbon 3 now it to obliterate 3-phosphate so you love you loose a phosphate on carbon 1 because that phosphate is donated to ADP to form your first ATP molecule and since this stuff involves the transfer of ATP a transfer of phosphate I mean ok from the high energy molecule ones will be PG to ADP to form ATP then this is catalyzed by a transferase ok because it catalyzes the transfer of phosphate group ok next step is from bliss rate 3 phosphate to glycerate 2 phosphate so the only difference is this number from 3 to 2 ok but everything stays the same is Douglas rate with the phosphate so there's only a change in the position of the phosphate and therefore this is catalyzed by an isomer an isomerase ok so I summarize means you know transfer of a functional group within the molecule alright first for step 9 conversion of glycerate to phosphate phosphate in entire movie so structures we need to see the structures of these 2 molecules in order for us to predict the type of an enzyme that catalyzes it catalyzes this reaction so without the structure it's really kind of hard to determine or guess the the class of enzyme if you just analyze the names it's it's pretty difficult so for this our conversion you need the enzyme ligase ok guys so keep in mind this reaction also involves release of water hydrolase you need to add water ok but this is not hydrolase it's not this is not catalyzed by hydrolase because it's all releasing water so it's lies and then for the last step of like all phosphoenolpyruvate or peeve PEP for short take note that this is also the second high energy molecule in our chart from from the last chapter from the previous chapter and therefore this also can donate phosphate group or phosphoryl group to ADP to form ATP so this is the second of ATP molecules produced in glycolysis so from phosphoenolpyruvate to pyruvate okay which is the one of the products of our glycolysis pathway so keep in mind that all these intermediates are three carbon molecules so in a fibre of eight which is one of the final products of glycolysis is a three carbon molecule as well so because you see you don't you don't see any any carbon dioxide being one of the end products okay or side products which means you didn't release any carbons of glucose so essentially glycolysis splits your six carbon glucose into three carbon molecule pyruvate and before I forget to step 10 is catalyzed by the enzyme transferase so here here the specific name of the enzymes catalyzing each steps of each step of the glycolysis pathway so for step one this is catalyzed by your enzyme hexokinase so hexokinase means it's a multi-enzyme complex a hexose or six so it's a hexameric on enzyme kinase is a specific term for transferase that cattle catalyzes the transfer of phosphate groups so kinase and then the second enzyme is phosphoglucose isomerase okay converting glucose to fructose so that's an isomer okay constitutional isomer and then third is phosphofructokinase again you see the word kind is there so transferring the the phosphate and then aldolase aldolase is delays for the next step so essentially once you have the fructose 1 6 bisphosphate which you see this is a very symmetric molecule right you got the phosphate here and a phosphate there and then you have the O in the middle so essentially this is cleaved the molecule is cleaved on this side right there so you got one two three carbons and then one two three carbons alright so that's that's your aldolase enzyme catalyzing catalyzing the the split-up row plus 1 6 bisphosphate into glyceraldehyde-3-phosphate so that's your glyceraldehyde 3-phosphate right there and the hydroxy acetone phosphate okay and then you have the triose phosphate isomerase obviously pond or die some race ok converting die hard to see acetone phosphate into glyceraldehyde 3-phosphate so sometimes you'll see abbreviation for glyceraldehyde 3-phosphate as g3p okay so that's glyceraldehyde-3-phosphate and dihydroxyacetone phosphate is d h AP okay all right from the energy investing stage that the glyceraldehyde 3 phosphate or g3p so now it enters your stage 2 which is now running duplicated ok so this next step or next step of glycolysis or the first step of stage 2 is a redox reaction remember and the enzyme catalyzing this redox reaction is glyceraldehyde-3-phosphate dehydrogenase so again another clue for a redox reaction so if you see the word dehydrogenase so meaning it is the redox reaction and then the 1 3 bisphosphoglycerate 2 3 phosphoglycerate so this is now your use of the high energy molecule to produce your ATP molecule so this this process of making ATP using a high-energy molecule okay it's called substrate level phosphorylation okay it's an it's a reaction that produces ATP in the cell there is another phosphorylation that our cells use to make most of our ATP's okay and that is your oxidative phosphorylation so these are the two ways of producing ATP molecules in the cell through substrate level phosphorylation and second is oxidative phosphorylation most of our ATP's are produced using oxidative phosphorylation which is the end of the metabolic pathway for for burning glucose molecule but you can also use substrate substrate level phosphorylation wherein you are using a high-energy molecule to transfer its phosphoryl group to ADP to form ATP okay so this conversion is cut by phosphoglycerate kinase you see the word kinase transfers eight phosphoryl group to another molecule and then from 3 phosphoglycerate to 2-phosphoglycerate so from the structure you see this is Foss phosphate in carbon 3 now it translates transferred to Cart to carbon 2 so that's an isomerase phosphoglycerate mutase the mutates is a specific term word for a summarize catalyzing this step and then the next step is conversion from four to phosphoglycerate to phosphoenolpyruvate and this is catalyzed by interlace which is a a form of lice okay so if you remember the definition of lyase there's an involvement of formation of a double bond and then the last step of glycolysis is catalyzed by pyruvate kinase again the word kinase transferring phosphate from eight from another high-energy molecule PEP to adp to form ATP in pyruvate so again this is your another another step up producing ATP through substrate level phosphorylation alright the first step of glycolysis is essentially to trap glucose in the cell to begin the glycolysis so upon entering of the glucose through a specific transport protein which is called gluten to Glu T so glucose transport proteins it stands for glucose transport protein and you have five five kinds of glute protein loop one Gloup Gloup two group three four and five depending on the type of cells so but essentially once the glucose molecules enters the the cell it is readily phosphorylated by the hexokinase okay at the expense of ATP to produce glucose 6-phosphate so essentially what happens here is the glucose becomes more polar and there's no transport protein to let this glucose 6-phosphate to get out of the cell so it essentially is trapped inside trapped inside the cell so this is your hexokinase on the enzyme and you have the two bindings or active sites or binding sites for both ADP and and glucose molecule so essentially these two lobes okay they come together okay so it's kind of squeezing a deep in glucose and force these two molecules to react so that the the ATP transfers its phosphate to glucose and forms the adp and glucose 6-phosphate so this uses the strategy of orientation in approximation okay exert its enzymes activity on these two molecules and these two substrates so the second step is isomerization of glucose 6-phosphate to fructose 6-phosphate which is catalyzed by forceful glucose isomerase so in this mechanism you have you see this reversible reaction so by the way the first reaction is essentially irreversible because you want the glucose to be trapped inside the cell okay so that's irreversible second step is reversible right there and for this mechanism the glucose 6-phosphate Wichitans in a cyclic form becomes open chain form in the introduction of this enzyme it converts itself to fructose 6-phosphate open chain and then cyclic structure so this step is essentially preparing the the glucose molecule to become symmetric before we cleave it into two 3-carbon molecules ok the DHAP and the g3p so this next step is an irreversible reaction catalyzed by the enzyme phosphoprotein kinase and sometimes it's abbreviated as PF k k phosphofructokinase essentially you see you add another phosphate into carbon two carbon one this is fructose 6-phosphate so that's phosphoryl group on carbon one carbon six i mean and then this second phosphorylation adds the phosphate to carbon one so now you see this is essentially symmetric molecule symmetrical molecule and this is irreversible reaction as well okay so it's irreversible reaction so in this step now the six carbon fructose is cleaving two to three carbon fragments or molecules and this step is reversible catalyzed by the enzyme aldolase in the products of this of this reaction of this step is your two simplest ketosis and simplest Aldo's the dihydroxyacetone phosphate phosphorylated simplest ketose and then this is deep phosphorus phosphorylated simplest aldose the glyceraldehyde 3-phosphate so so sometimes you'll see the abbreviation GA P instead of g3p so these these two mean the same thing so DHAP for diehard see acetone phosphate gaap for glyceraldehyde-3-phosphate and as I mentioned earlier the glyceraldehyde 3-phosphate is the only one that can enter stage 2 of glycolysis and therefore to not not waste any carbons ok of your glucose molecules so your DHAP has to be converted into glyceraldehyde-3-phosphate as well in the process of your enzyme triose phosphate isomerase ok and at this point glycerol behind 3 phosphate can now enter the stage 2 and stage 2 will be run in duplicate alright so this step is the only redox step in your glycolysis pathway ok so specifically in this step you oxidize the aldehyde and when you oxidize the aldehyde you this is accompanied by the addition of the inorganic phosphate at this position so as you can see there is a loss of hydrogen so oxidation means loss of hydrogen or gain of oxygen atom right or oxidation increase in oxidation number reduction decrease in oxidation number so that's essentially what happens to the aldehyde of glyceraldehyde-3-phosphate the gaap and this is also involves the gain of electrons of NAD+ forming your na d h and this is catalyzed by this glyceraldehyde 3-phosphate dehydrogenase so as I've said when you see the word dehydrogenase automatically did that is a oxido reductase so this step is what you call the formation of your high-energy molecule one three BPG so after we form that high energy molecule or you know high energy transfer transfer hospital transfer potential molecule then we are going to use that to make ATP okay our first ATP form in your glycolysis pathway so from this high energy molecule we use the phosphoglycerate kinase to convert one to BBG to 3 phosphoglycerate so essentially what happened was one three BPG becomes just three because you transfer a phosphate or phosphoryl group to adp to form your ATP in a subset this step is your substrate level phosphorylation step in like alysus alright next step is the conversion of the 3 phosphoglycerate to phosphoglycerate by phosphoglycerate mutase which is an isomerase essentially the established to prepare preparing the molecule to for the formation of the second high energy molecular high transfer hospital transfer potential molecule so once to 2-phosphoglycerate is formed then the next step which is the affirmation of phosphoenolpyruvate occurs in the presence of the enzyme in lace so in a lace is a type of lies okay so now you see the formation of double bond right there and this is a high-energy molecule in the main reason for that is because of that unstable enol tautomer okay so it wants to form a more stable molecule pyruvate so it has to release that stored energy through the this the next step were the last step of glycolysis which is the formation of the second ATP molecule okay by the action of pyruvate kinase so if we look closely at the last step of glycolysis for the phosphorylation of adp okay forming ATP so this is your high energy molecule PEP forming the enol form of pyruvate and eventually forms the state most stable form of pyruvate okay so this is catalyzed by the reaction by the enzyme pyruvate kinase okay and again as i've said earlier so this is using a high-energy molecule to form ATP this is another or the second substrate level phosphorylation in psychosis pathway right net reaction for glycolysis if you start with one molecule or one mole it doesn't matter one molecule of glucose then these are the three important products of glycolysis two pyruvate molecules two ATP molecules and two NADH molecules so why do we have two ATP molecules form in this from this pathway when remember that stage two of course in duplicates so why not four molecules of ATP so the main reason is that that's the gross ATP you so the gross ATP yield is four but the net is two since we use two molecules of ATP on on the energy investing stage of glycolysis all right so let's look at the free energy values of each reaction steps in glycolysis pathway and so you can see you got two columns here the Delta G naught prime and the Delta G values so this is a standard condition at physiological pH standard constant concentration but this is actually what is what is more important because this Delta G is the actual free energy change for each step in makalah psious so as you can see these are the three highest so don't worry about these numbers in parentheses so these are your K Cal's per mole let's just focus on kilojoules per mole so the first step right here and then there's the third step which also has a high negative Delta G and this last step okay so these are the three irreversible steps steps in glycolysis pathway so meaning they are highly spontaneous and the reverse is highly non spontaneous so you also can see some of the positive Delta G steps okay so but these are kind of small kind of small positive Delta G's and therefore they are essentially being pushed forward because when you add all these Delta G's to get the net Delta G value of the rate of the whole metal glycolysis pathway so you're gonna get the net negative Delta G so essentially everything should be moved in the forward direction all right so since we're using NAD+ okay to form the activated electron carrier NADH so this molecule must be regenerated from the metabolism of pyruvate so and the main reason for that is if you want to continue ATP synthesis so we need to regenerate NAD+ by reoxidized seeing NADH molecule remember NADH is an electron carrier so it carries two activated electrons they they their main role is to carry electrons and dumped dump the electrons to the next pathway okay so to [Music] regenerate NAD+ we need to either use further oxidation steps okay our pyruvate to co2 which essentially is the next pathway the Krebs cycle okay or we can regenerate NAD+ by ethanol fermentation or by lactic fermentation so by the way NADH it is a vital coins time that is used for variety of pathways and this is derived from the vitamin b3 or niacin so chicken is a good source of vitamin b3 so these are the three phases of pyruvate so again in order for us to regenerate NAD+ so from pyruvate which comes from the anaerobic glycolysis pathway so we can either use this route okay - which is further sorry so this is the further oxidation of the carbon molecules of pyruvate and or we can use the ethanol fermentation or the lactic acid form datian all right it's the first method off oxidized oxidizing NADH to form nad plus to regenerate NAD+ so from your pyruvate which is the one of the products of your glycolysis you will remove one carbon as co2 by the action of pyruvate decarboxylase for the for forming acetone behind molecule you'll see that acetaldehyde molecule only has two carbons so from a three carbon molecule to a to a carbon molecule so this decarboxylase is essentially catalyzing the cleavage of this carbon-carbon bond and therefore this is a type of lice okay and then once I set of the height is formed then the set the next step would be formation of your ethanol and on this step this is where the nad plus is regenerated by the ox by the oxidation of NADH from NADH which is the reduced form to NAD+ which is the oxidized form in the presence of alcohol dehydrogenase so you see the word dehydrogenase so this must be an example of an oxido reductase and also since you see that those two are your coenzyme involved for this step this is a redox reaction for sure and this is called the alcoholic fermentation alcohol fermentation which leads to the formation of two ethanol molecules it is only used disuse by some some bacteria we cannot we cannot do this we cannot form our own on ethanol from pyruvate molecule so this is just a bigger picture of the previous slide so you've seen this conversion for alcoholic fermentation starting from pyruvate forming acid aldehyde and eventually forming ethanol molecule this is just connecting it to the rest of your glycolysis pathway here is another way of oxidizing NADH that regenerates your NAD+ or by oxidizing NADH forming nad + pyruvate is converted to lactic acid or lactate in the presence of lactate dehydrogenase so again this is an oxidoreductase the reductase enzyme so this is conversion of one of glucose essentially but because pyruvate comes from glucose into two molecules of lactate why two molecules again because remember from one glucose molecule you make two pyruvate molecules and then for each pyruvate you make lap one lap date so total up to lactate molecules so the same for the first way of make of oxidize NADH through alcoholic fermentation so one glucose molecule forms two ethanol molecules and again so we're seeing the bigger picture of how NADH is oxidized to regenerate NAD+ and how any d+ will be used for glycolysis to continue glycolysis reaction so this is your pyruvate to lactate acid or ethanol fermentation and this is how they use in and regenerate regenerate NAD+ alright so what about other sugars such as fructose in galactose so how are we able to use these other sugars okay to to it extract energy okay or to make ATP so fructose from say high fructose corn syrup or galactose from milk okay they cannot just be entering psychologists without themselves convert converted into by coletek intermediate so they need to be to become glycolytic intermediates first before they can enter the glycolysis for example the galactose sugar needs to be converted into glucose 6-phosphate okay so that's the entry point that's the entry point for galactose sugar okay conversion galactose must be converted to glucose 6-phosphate and then once it becomes glucose 6-phosphate sandakan can continue to form the pyruvate fructose on the other hand enters the glycolysis pathway by turning itself into fructose 6-phosphate okay proto six phosphate this is mainly in the adipose tissue and if the fructose is goes to the liver then it turns into DHAP or GAAP okay and enters the glycolysis essentially entering the second stage of glycolysis the energy generating stage to form the pyruvate molecules so so again these two molecules they cannot just directly enter the glucose glycolysis pathway without forming turning them into AG like glycolytic intermediates okay so by doing in the liver this is the conversion from fructose to DHAP or fructose to GAAP is accomplished by this pathway the fructose one phosphate pathway so we're not going to focus on this pathway you only need to remember from this slide is how Maalik of sugars other than glucose enter your glycolysis and this is really really interesting especially for those because remember the fructose is not it's not really good for our body because too much intake of fructose from high fructose corn syrup HFCS you probably heard this abbreviation okay it actually leads to metabolic syndrome such as diabetes or you know you you become you may become obese okay so fructose fructose in the adipose tissue this is how it and protists enters the glycolysis so essentially it's bypassing D the first irreversible reaction okay the first irreversible reaction is catalyzed by the first enzyme hexokinase in that hexokinase enzyme is highly regulated so it's like a major intersection or major traffic light so it's highly highly regulated so by pat fructose bypassing that could mean that fructose will be supplying a lot of part of intermediates that may lead to obesity for example this is what's worse if the fructose is in the liver and and enters the the calluses pathway and essentially when fructose enters this enters the glycolysis pathway through this entry points it bypasses two major irreversible reaction which is which are highly regulated and steps in glycolysis okay so it will it bypasses the hexokinase k catalyzing the first irreversible reaction it also bypasses the PF k step gained the force of photo kinase step which is the second irreversible reaction alright