How many steps in gluconeogenesis are not the exact reversal of the steps in glycolysis? What kind of conversion of substrate to product does each involve? What is the common theme in each of these reactions?

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Hi, everybody. Let's take a look at this next problem. It says, determine if the statement is true or false, correct the statement if it is false. So our statement here is three steps in glycolysis are not the exact reversal of the steps in gluconeogenesis. Each of them involving a conversion of substrate product where the common theme is is summarization. Well, this one's a little bit confusing to wrap our minds around at first. So let's break it down. So first off, we're comparing the processes of glycolysis and gluconeogenesis. So recall that these are essentially reverse processes. So in glycolysis, we start the process with glucose and we end up with pyre that first part of the process of the breakdown of glucose metabolism of glucose to obtain energy. In gluconeogenesis, the body is synthesizing glucose and this process starts with py vate. We have various other molecules that can be converted into pyruvate. And then the pyruvate goes through a series of reactions to give us glucose as a product. So right away, we can recall that these cannot be a complete reverse why? Because glycolysis, it is a highly aaronic process. That's why it generates a TP. So it has part now it has a lot of steps. Right? Glycolysis has depending on exactly how you delineate them and some books can do this differently. Um Glycolysis has 10 steps. We go, Genesis has about 11 steps again, can be numbered sort of differently here. So it's this complex process, but overall, it's generating a lot of energy, you're breaking down glucose. So synthesizing glucose trying to reverse this highly energon process is going to be tricky specifically in glycolysis, three of the steps are irreversible. So while the other steps in the process have an equilibrium which could be tipped one way or the other, and so could theoretically just occur in reverse. Three of the steps are so ergo that they just won't go the other direction. So essentially we have to bypass those three irreversible steps. So part one of our question that says three steps in glycolysis are not the exact reversal. The steps in gluconeogenesis, this would be this part would be true because we have those three irreversible steps. So we need an alternate pathway. We can't just run this reaction in reverse because it won't go that way. So this part is true, but now we have part two, it's saying that each of these three steps involves a conversion substantive product where the common theme is isomerization. So substrate and product, the only difference is they're isomers of each other. So to determine whether this is true we need to look more closely at the three reactions that are irreversible in glycolysis and look at what is going on in those reactions. So, if we do kind of a side by side comparison here of the two processes, let's start with the first part of gluconeogenesis and the last part of glycolysis. So that would be a conversion of pyruvate to pe p in gluconeogenesis. It has this alternate pathway that goes um from pyruvate to oxalacetate to pe P. And that's because in glycolysis, this is an irreversible reaction going the other way from pe P to pyro. So we have this alternate pathway here and then we put a little sort of red brackets to talk about the next part where we then have a number of steps that are reversible. So we can just run them in reverse. We draw the little equilibrium arrows here to indicate this is a reversible reaction and that ends up with in gluconeogenesis going from pe P and ending up with fructose 16 bisphosphate. So I'm just putting an abbreviation there. And of course, we're looking at the backwards process in um and then one more set of reactions that come to equilibrium when we convert our fructose six phosphate to glucose six phosphate. So that again is one where it can just be the reverse process. And then our final irreversible step in gluconeogenesis is the conversion of glucose six phosphate to good old glucose where we're going in the end and then like why is the irreversible step going from glucose to glucose six phosphate in um glycolysis, which would be step one in glycolysis. So we see we have steps 13 and 10, which are irreversible. So let's look at what is the common theme of these is it isomerization. Well, we have the names of these um reactions or the names of the products and reactants to give us a clue. So let's look at these, we have in step one, you're converting between glucose and glucose six phosphate. So we've got the difference is a phosphate transfer. And then in step three, going from fructose, six phosphate to fructose, 16 bisphosphate. Again, we've got a phosphate transfer, one or two groups on fructose. So another phosphate transfer. And this makes sense, right? Because when we think of irreversible reactions and reactions that could be highly egoic, we know that phosphate transfers have that quality, which is why a TP is that energy source for the cell? And then finally, our last irreversible reaction, we have an abbreviation that makes it a little trickier. But let's recall that pe P stands for phosphoenolpyruvate. So we see that phospho in there which tells us that this also between pe P and pyruvate is another phosphate transfer. So part two here is going to be false because these are not isomerization, these are phosphate transfers. So the correct statement should say three steps in the glycolysis are not the exact reversal of the steps in glucon neogenesis, each of them evolving. And then we're going to correct this. We'll write it in red. A phosphate transfer should be our correct statement. So there we go. Our correction of our false statement. See you in the next video.

How many steps in gluconeogenesis are not the exact reversal of the steps in glycolysis? What kind of conversion of substrate to product does each involve? What is the common theme in each of these reactions?

Verified video answer for a similar problem:

Key Concepts

Gluconeogenesis

Key Regulatory Steps

Energetics and Regulation