all right, Step one of the citric acid cycle is carried out by citrate synthesis and notice that nice negative Delta G. Remember, this is one of those driving steps of the citric acid cycle, and in the process of this reaction, we have our acetyl coa a ox alot acetate. We add water in. We bump off that CO a see you later and we are left with citrate right here. Now the following reaction reaction Number two is carried out by a con, a taste, and you might notice that it's listed as having a positive Delta G notice, though, that that's the Delta G prime. Not so actual cellular conditions. This Delta G is closer to zero, so it's It's a readily reversible reaction here. Citrate is going to be turned into this enzymatic intermediate sys con a tape you can see right here in the middle, and then ultimately it's turned into is a citrate. During this process, we remove water and then we actually add water back in. That's why again, sometimes called the Ferris wheel, it's kind of like doing a turn. Um, what is interesting to note and also important to note about this reaction is that citrate is pro Cairo, and what that means is that even though it's not actually a Kyrill molecule, it behaves as if it were Cairo. And that's because a con a taste, a condom, taste binds citrate in one orientation. It's it's just, you know, it just happens this way it's not. You don't need to know why this is, but just notice that this is a also symmetric molecule. I mean, this right here, that's just Samos ch two right there, just drawn it out. So this is not a Cairo center. However, um, you know, uh, like right here is always where this double bond is gonna be formed. You know, the the citrate wouldn't go in in the other orientation and have it be formed. There just happens that way. And we call that property pro Cairo. Meaning not actually Kyrill, but behaving as if it were Cairo, Uh, something about a con. A taste that's interesting to note is it contains these iron salt for complexes, which are actually held into the enzyme. Bye Sistine residues. Um, and this is not gonna be the last time we talked about iron sulfur complexes. those. They're gonna come up in the next review when we talk about the electron transport chain because there's a ton of them in there. And what's what's cool about a contest in terms of these iron sulfur complexes, is it? It's actually an iron response regulatory molecule. So when there is a lack of iron, it's going to change shape. And when it changes shape due to this lack of iron, excuse me, it can actually bind RNA, and if it binds RNA, it will turn on off various genes. And what what's gonna happen is when iron is high in the blood fair written, this molecule ferreting is going to be produced. And when iron is low in the blood, this molecule transparent is going to be produced. So kinda cool. Kinda taste has this auxiliary function right? It's not just an enzyme that's part of the citric acid cycle. And again, this kind of continues the theme that, um, biology re cycles things right. It always finds new purposes for, uh, old creations. It's always innovating. So third reaction of citric acid cycle is carried out by isis citrate di hydrogen iss. We are going Teoh Teik isso citrate form Alfa Kita glued a rate which I am blocking right now. Beautiful Alfa Keto Gluten rate a Alfa K G. I'm just abbreviating it that way because I'm being lazy. Um, now kind of a couple interesting notes about this reaction. A zoo we've already said it generates and a d. H and releases a CEO to, um, you know, definitely important to note. Also, just to be crystal clear here is our co two that's coming off. So that is our released CO two. And, uh, you know, that makes this enzyme an oxidative de car box. Lace notice how we are oxidizing that alcohol and it uses an 80 plus or and a D p plus as theorem Tron except, er, however, for for us for humans, we're gonna be using N a. T h Thio generate on. I'm sorry in a D plus to generate an a D. H. And, uh, it also uses mag unease as a co factor it does not use, even though it's a d hydrogen e. So, you know, we're going to talk about a couple D hydrogen aces here. First one was Piru di hydrogen is this is our second, right. Uh, isso citrate di hydrogen is but this one is not going to use tpp lip poet and F A D and Co A. It's not going to use those molecules like Piru di hydrogen is did. However, Alfa Kita glued a rate di hydrogen is which we're gonna talk about in just a moment is going to use, uh, all this stuff, which is why I point out here, that is a citrate. Doesn't use it, right? I used to situate doesn't use it, but Piru di hydrogen It's an Alfa Kita glued or 80 hydrogenated do use this stuff. So don't go, you know, thinking like all the hydrogen aces are using, uh, those same molecules. All right with that, let's flip the page.
