The citric acid cycle contains four 4-carbon dicarboxylic acid...

Question

The citric acid cycle contains four 4-carbon dicarboxylic acids.

a. Name them.

Accepted Answer

Hello everyone. Well, let's look at our next question. Which of the following sets of compounds are all four carbon dic carboxylic acids involved in the citric acid cycle. A citrate isocitrate, succinate and fumarate. B oxalacetate malate, fumarate and succinate. C acetyl coa citrate isocitrate and alpha ketoglutarate or D succinyl coa alpha ketoglutarate malate and oxalacetate. So, first of all, hopefully, as we read through this, these names should be familiar to you and you notice that all of our four answer choices, all of the compounds mentioned are involved in the citric acid cycle. So put a little check mark there that has that condition has been met. So we've got two further conditions. They need to have four carbons and they need to be dic carboxylic acids. So they need to have two carboxylic acid groups. So two coo minus groups. Now, the four carbon condition is much easier to identify since it's a pretty good idea to be familiar with how many carbons each step of this cycle has because that's how we keep track of where carbon dioxide is being produced, how much glucose is being, you know, there's a lot of questions always involving how many cycles do you have to go through to break down glucose, things like that? So that's a good thing to just always know, but we don't always know right off the top of our head, the exact chemical structure of each component. So let's start looking at the numbers of carbons. So I'm going to post a sort of basic diagram of the citric acid cycle. This is kind of the outline I like to keep in my head for referring to when I think about this cycle. Uh Not every detail is on here, you have your own way of remembering these things. Sometimes I like to just jot this down on a test to help orient myself. So let's focus on the number of carbons here. So we know that we start with acetyl coa coming in. It has only two carbons. So I'm highlighting that in yellow where I've written that and it combines with oxalacetate and I don't have this written here since oxalacetate is my last step, but Oxyl acetate has four carbons. So I'll highlight that as well. So right off the bat, we know at least one of our answer choices had acetyl coa in it and that only has two carbons. And since our question says that all of the compounds in our answer must be for carbon, we can rule that one out right away. So let's look at choice C which has acetyl coa as one of the compounds. So just cross out choice c right away. So as I said, looking at the number of carbons is kind of a little bit of a shortcut to our answer here. So let's keep going. Acetyl coa all oxyl acetate combined. Now we've got six carbons total in the product which is citrate. So citrate has six carbons. Well, we had citrate in some of our answer choices. So choice A started with citrate. So just cross out a right now. So we're down to B and D already. Now in our next step, citrate form, it goes through an isomerization and we form isocitrate. I didn't write that specifically. So I'll just jot that in there. And again, it's just isomerization. We don't change the number of carbons. It's six carbons as well. Well, isocitrate isn't one of our answer choices. Um are two of them I should say, but it's A and C which we've already ruled out. So that doesn't help us any in the next step. That's a decarboxylate produces carbon dioxide. And so therefore, we go down by one carbon. So our product alpha ketoglutarate has five carbons. Now. Well, we had alpha ketoglutarate in our answer. Choices in choice C which we've already ruled out and then choice D which has alpha ketoglutarate. So let's cross that out. Well, just by doing those steps, we've already eliminated three answer choices and we have our answer. So you can see how focusing on the easier step, it got us to the answer relatively quickly if we were on a test without a lot of thinking through the exact chemical structures of these compounds in the cycle. This is a practice, practice question. So if you'd like stay tuned, we'll walk through this just a little more thoroughly. Um But that we've already zoomed in on our answer of choice. B So we're down to alpha ketoglutarate with five carbons. The next step, another decarboxylate loss CO2. So we are down to four carbons now. So we have succinyl coa. Now, one thing to notice is we've started at succinyl Coa has four carbons. We know that our last product is oxalacetate, which also has four carbons. So we know from here on out, all of the compounds in the cycle will have four carbons. And so we have five compounds left, we're looking for 44 carbon compounds. So there's really only one that we'd have to think about our carboxylic acids, but it's ruled out already by being combined with something else that's already been ruled out. So succinyl Coa was in choice D which we already ruled out. So we'd know even without understanding its chemical structure that it is not in our correct answer choice. But if things were arranged differently, we would have to rule out one of these four carbon molecules and that would actually be succinyl coa. So succinyl Coa has just one carboxylic acid group and then it has one ketone, but then it has that s and then co a on it that is removed in the next step to form succinate. So by succinate, you have two carboxylic acids and every molecule from then on. So we'll put two oops coo minus starting with succinate all the way through oxy acetate. They all have two carboxylic acid groups. So succinyl coa has the right number of carbons but only one carboxylic acid group. So everything else, as we say, we don't lose any more carbons. So we still have four carbons. So our answer to which of the following sets of compounds are all poor carbon dic carboxylic acids involved in the citric acid cycle is choice B oxalacetate malate fumarate and succinate. See you in the next video.

The citric acid cycle contains four 4-carbon dicarboxylic acids.
a. Name them.

Key Concepts

Citric Acid Cycle

Dicarboxylic Acids

4-Carbon Intermediates

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