Practice - Glycolysis 2 - Video Tutorials & Practice Problems
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Practice - Glycolysis 2
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If you haven't done question 26 yet, pause the video now. The molecule 2 fluorot-2deoxyglucose is used as an imaging agent to detect tumors and the way this works is that cancer cells will actually have really high rates of glycolysis and, in using this molecule, basically what we have is a molecule that looks just like glucose except, the carbon 2 position is no longer bound to a hydroxyl group. Instead, it's bound to this radio labeled fluorine right there, F18 or fluorine 18. So this radio labeled fluorine is an atom that imaging technology like a CT scan can pick up on when you do a scan on someone. So, remember that when glucose enters the cell, first thing that happens to it is hexokinase phosphorylates it, right? And that traps it in the cell and it also, you know, tricks the concentration gradient for glucose to allow more glucose to enter the cell. In the case of this molecule, when it enters the cell, it's going to be converted into 6 phospho FHDG which is fluorodeoxyglucose and basically, the idea is, this will trap it in the cell, meaning that cancerous cells which are going to to have high rates of glycolysis are going to trap a lot of this molecule in the cell. They're going to sequester a lot of it, meaning they're going to, have a very strong glow when, CT scan is performed because they're going to have a lot of that F18 in there. So, that is how this molecule is used as an imaging agent to detect tumors. Now, in an anaerobic muscle preparation, lactate formed from glucose, with the C2 position, labeled would be labeled in So let's think about this. The answer is the alcohol carbon but let's think about this. Here is pyruvate. And recall that this will be carbon 1 or 6 from glucose, this will be 2 or 5, and this will be 3 or 4. Now, in lactic acid, fermentation, pyruvate is directly reduced by NADH regenerating NAD plus and this forms lactate and lactate looks like this. It looks just like pyruvate except we have reduced our ketone. Woah. Our ketone to an alcohol. So the numbering is still the same. So here on the carbon attached to the alcohol is where carbon 2 from glucose would wind up. Now, glycerol is considered a non fermentable sugar because it produces too much NADH to be efficient. It produces, an extra NADH, over other 3 carbon molecules. Meaning, meaning that if you were to use glycerol and do fermentation, you would actually slowly be accumulating excess NADH. You can't you would not be able to replenish your NAD plus at the same rate that you produce NADH because you'd be producing too much NADH from glycerol. So, it is not considered a fermentable sugar. Meaning it's only going to be used in aerobic conditions when cellular respiration is going to occur because the NADH will be used up in electron transport then as opposed to just building up because we're relying on fermentation to replenish NAD plus Now, while most reactions of glycolysis are easily reversible, reactions 1, 3, and 10 are irreversible and drive the pathway forward And this is because they have a a very negative delta g. Remember, these reactions are reactions of hexokinase, phosphofructokinase, and Oops. Pyruvate. It's getting all ugly in there. Pyruvate Kinase. And these 2 both cost ATP. And this reaction generates ATP. So, they're all very favorable reactions, meaning they're not easily reversible because they have a very negative delta g. And so when we do gluconeogenesis, these are the enzymes or the reactions that require new enzymes to go in the opposite direction. Alright, last question. Phosphoglucoisomerase also known as phosphohexo isomerase, same enzyme, catalyzes the second reaction in glycolysis. Diagram the reaction in the glycolytic pathway and be sure to show all atoms of the substrate and product. Alright, I've drawn this in ahead of time. So, if you haven't, drawn this out yet, pause the video now, draw it out and I'm going to reveal the answer. I drew it in ahead of time just to save time. You don't need to watch me draw out this whole molecule or both of these molecules. That is a waste of time. So we start with glucose 6 phosphate. Let me hop out of the image here. We start with glucose 6 phosphate. We need to use magnesium. Our enzyme needs magnesium for this reaction and we wind up with fructose 6 phosphate. So we do a rearrangement and notice that here we have our carbon 2 and now here is our carbon 2. So we have rearranged the ring in the course of this reaction. Alright, let's flip the page.