Look ahead to Figure 21.8 for the citric acid cycle.
b. What class of enzymes carry out these reactions?

Question

Look ahead to Figure 21.8 for the citric acid cycle.

b. What class of enzymes carry out these reactions?

Accepted Answer

All right. Hello everyone. So this question says in step six of the citric acid cycle, determine the class of enzyme involved. Option A says oxidoreductase. Option B says transferase option C says hydrolase and option D says ligase. So let's go ahead and start by giving an overview of the citric acid cycle as a whole. Right? Recall that the citric acid cycle otherwise known as the TC A or CREB cycle is the third stage in catabolism for aerobic organisms. Now catabolism if you recall describes metabolic pathways in which larger starting materials are broken down into smaller products. So the citric acid cycle notably is going to produce at P as well as carbon dioxide. And this cycle is set to start at acetyl coa. So acetyl coa is converted further into carbon dioxide as well as other co enzymes along the pathway. And A TP is produced as a result of some of those steps. So with that in mind, I just very briefly want to talk about the steps of the citric acid cycle by talking about the organic intermediates that are created as a result of each step of which there are eight. So here. I'm just listing out the eight steps to go through. Now, do keep in mind that as mentioned before, we do have other products such as A TP and FA DH too. But for the purposes of this overview, I just want to focus on those organic co enzymes. So anyways, let's start with the first step, right? The first step is the conversion of Aido Koe and oxalacetate into a molecule known as citrate. In the second step citrate is isomerize to produce isocitrate from there. In the third step, isocitrate is converted into alpha ketoglutarate. And in the fourth step, alpha ketoglutarate is converted into succinyl coa in step number five, succinate is converted into succinate. In step six, we have succinate being converted into fumarate. In step seven, fumarate is converted into malate or mate as you may have heard it before. And in the last step of this cycle, we have mate being converted into oxo acetate. And then the cycle can repeat itself because the oxalacetate created in step eight can react with another equivalent of aceto koa and generate citrate all over again. So from here, let's focus on the reaction in question here, which is that step six. So step six of the citric acid cycle is the oxidation of succinate to produce fumarate. So here sum it is a four carbon compound and it's characterized by of course, there being four carbons in total, but carbons one and four contain carboxylate groups and there's a double bond between carbons two and three. So, working backwards now to generate the starting material, succinate is going to look very similar to fumarate. But the only difference is that there is no double bond between carbons two and three. So we have the same, we have the same two carboxylate groups on carbons one and four. But this time, there's only a single bond between carbons two and three. So in this step of the citric acid cycle, we have succinate, reacting with F ad to eventually produce fumarate, establishing a double bond between carbons two and three and transferring those electrons to produce fa DH two. Now, just for your information, the enzyme that catalyzes this reaction is known as succinate dehydrogenase. That's because succinate is being oxidized into fumarate. So with this in mind, now that we've talked a little bit about citric acid cycle as a whole. And also the specific step, let's just go ahead and discuss the categories of enzymes listed here in the answer. Choices starting off with option D which is a lie gase. Now, a liga contains the word or at least part of the word L gate, which means to bind two things together as such lie cases, catalyze the bonding of two substrate molecules. So it's going to take two substrates and combine them together or ligate them. On the other hand, hydrolysis catalyze hydrolysis reactions. So what's happening here with a hydrolase enzyme is that the hydrolase enzyme is going to catalyze the breakage of a bond by adding water across that bond. Moving on here, we have transfer races and trans races essentially move functional groups. And very briefly, I want to talk a little bit more about transfer vases and distinguish them from isom erases because it's easy to get those mixed up. So a transferase is going to transfer a functional group from one compound to another. An isomerase is going to simply rearrange atoms that are already within a substrate. So transfers move functional groups between two different compounds. Whereas Isom erases change the connections between atoms in one substrate. So just to clarify that. So on the other hand, option A here is an oxido reductase which as the name implies, catalyzes redox reactions or oxidation reduction reactions. So, as mentioned before, succinate, dehydrogenase is catalyzing the oxidation of succinate into fumarate. Therefore, option A is correct because that is an oxidoreductase. And so with that being said, thank you so very much for watching and I hope we found this helpful.

Look ahead to Figure 21.8 for the citric acid cycle.
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b. What class of enzymes carry out these reactions?

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Key Concepts

Citric Acid Cycle

Enzymes

Enzyme Classes