Identify each step in glycolysis that is an isomerization.

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All right. Hello everyone. So this question is asking us, are there any steps in glycolysis that involve isomerization? If there are, what are the steps? Now, option A says that there are no steps that involve isomerization and options, BC and D say yes and propose different steps along the pathway that could involve isomerization. Now, just so we're clear recall that isomerization involves the formation of isomers. So essentially the product of a given step in the pathway should have the same molecular formula as the starting material. The only thing that changes is the connection between atoms in the molecule itself. So with this in mind, let's recall the fact that glycolysis is a pathway that breaks down glucose into Pruitt. Now pyruvate is a very important metabolic intermediate that's involved in several different pathways. And in addition to pyruvate glycolysis also produces some A TP as well as some N A DH, which is an important cofactor in oxidation reduction reactions. So with this in mind, I think it's going to be best to just talk about the glycolysis pathway as a whole. And then as we go through discuss steps that could involve isomerization starting off of course, with the first step. So because of this, this is the first step, we are dealing with glucose as our starting material and glucose in this first step of the pathway of glycolysis is converted into glucose six phosphate. So it's different here. Well, at this point, a phosphate group has been added to glucose and because a phosphate group has been added to glucose, one equivalent of ATP was consumed and one molecule or one equivalent of AD P was produced. This is because the phosphate group is transferred from a TP to glucose. Now, with that in mind, this is not isomerization because a new functional group has been added in the structure of our final product. So that's not isomerization moving on. Though in our next step of the pathway, we have glucose six phosphate being converted into fructose, six phosphate or fructose six P for short. Now, fructose six phosphate is in fact an isomer of glucose six phosphate. So, the second step of the pathway is in fact a summarization because our product that's fructose six phosphate has the same molecular formula as glucose six phosphate. The only thing that's different is the connections between atoms in the molecule. So from here, we're going to take fructose six phosphate in the third step of the pathway and convert this into Ruto 16 bisphosphate. Now, once again, the names can be very helpful, right. So at this point, we've taken fructose six phosphate and added an additional phosphate group. So here another equivalent of a TP must be consumed to produce ad P transferring that phosphate that phosphate group onto fructose six phosphate. Now, once again, this is not isomerization because we're adding a phosphate group. And so at this point, we have fructose, 16 bisphosphate. So the fourth step of the glycolysis pathway is going to essentially break down fructose six phosphate, which is a six carbon molecule into 23 carbon products. One of them is dihydroxy acetone phosphate or DH A and the other is glyceraldehyde three phosphate. So just to be extra, certain dihydroxy acetone phosphate and glyceraldehyde three phosphate are both products of the fourth step of glycolysis. So the fifth step is going to involve the conversion of dihydroxyacetone phosphate into another equivalent of glyceraldehyde three phosphate. So here, dihydroxy acetone phosphate is a ketone and glyceraldehyde three phosphate is of course an aldehyde. And so the conversion from one to the other is in fact a summarization because once again, we are not changing the molecular formula of the starting material. Now, at this point, it's important to also recognize that at this point, we have two equivalents of glyceraldehyde three phosphate after dihydroxy acetone phosphate is converted into a second equivalent. So from here, glyceraldehyde three phosphate is the relevant intermediate in the glycolysis pathway. And two equivalents of that results in two equivalents of pyruvate. So from here, we move on to step six of the glycolysis pathway because in step six, we're going to take glyceraldehyde three phosphate and convert this into 13 bis phospho glycate. So here, this step is remarkable in the sense that a phosphate group is being added, but we're not actually consuming a TP this time rather a phosphate group from the cytozole. In addition to some N ad positive is used to install an extra phosphate group to create 13 bis phospho glycate. And so in the process, we've converted N A positive into another equivalent or a new equivalent of N A DH. So from here right now were on step seven, we're going to take 13 bis phospho glycate and convert this now into three phospho glycerine. So at this point, the opposite has happened at least relative to what we've seen before, right? Because now a phosphate is actually being removed from the starting material. So we can take one equivalent of AD P and convert this into a tepee, taking the phosphate group from 13, this phospho glycate and giving it to adenosine diphosphate. So at this point, we have three phospho glycerine. So in the eighth step of the pathway, we was stunned is so clear, three phospho glycate is converted into two phospho glycate. Now, as the name implies, the only difference between the starting material and the product of this step of the pathway is simply that the location of the phosphate group has been changed, right. It's moved on the carbon chain. So here step eight of the gly glycolysis pathway is another example of isomerization. So let's go ahead and finish our pathway off right. In the second to last step of the pathway. That step nine, we are converting two phospho glycate into phospho AOL pub or pep for short. Now, the difference here is that water is being removed from two phospho glyceride to produce phospho ey pyruvic. So our final step involves the conversion of phosphoenolpyruvate into just pyruvate. So what changes? Well, namely the phosphate group in phosphoenolpyruvate is being removed. So similar to step seven of the pathway, we can take one equivalent of A DP and use this reaction to produce ATP. So this completes our overview of the glycolysis pathway. But I just want to very quickly restate the fact that after DH A P is converted into glyceraldehyde three phosphate steps, six through 10 are going to actually occur twice, once for every equivalent of glyceraldehyde three phosphate. So that's why for example, two equivalents of pyruvate are going to actually be produced after glycolysis, even though my diagram is only showing one. So just be mindful of that. But in any case for the purposes of this question, we've identified steps 25 and eight as the isomerization steps of glycolysis. So that means option C is our answer here and there you have it. So with all that being said, if you watch this video all the way through. Thank you so very much and I hope you found this helpful.

Identify each step in glycolysis that is an isomerization.

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Key Concepts

Glycolysis

Isomerization

Enzymatic Reactions in Glycolysis