in this video, we're going to begin our discussion on the different types of enzyme catalysis. So recall from our previous lesson videos that enzymes can actually lower the energy of activation required for a reaction in several different ways, including lowering the entropy of the system by bringing substrates closer together so that they can react faster, properly orienting the substrate so that their functional groups are also properly oriented. And they can react easier, distorting a substrate so that it can achieve transition state confirmations easier and dissolve ating a substrate so that the hydration shells do not interfere and slow down the reaction. And again, these air all different ways. The enzymes can lower the energy of activation that we already covered in our previous lesson videos. And so between all of these different ways, we know that there is still a common theme to stabilize the transition state. Now, what we haven't yet talked about are the different types of enzyme catalysis reaction mechanisms that enzymes use. And so what are some of those different types of enzyme catalysis mechanisms? Well, it turns out that there are four mechanisms that enzyme primarily use for catalysis and So the first is acid based Ca Tallis ISS. The second is electro static Ca Tallis ISS. The third is metal ion ca Tallis ISS and the fourth is CO Vaillant, CA Tallis ISS and so moving forward in our course, we're gonna talk about each of these different types of enzyme catalysis reaction mechanisms in their own separate videos. But in our next lesson video, we'll talk about the very first enzyme catalysis mechanism, which is acid based catalysis. And so I'll see you guys net lesson video.
Play a video:
Was this helpful?
So in our last lesson video, we said that there are four main types of enzyme catalysis, and in this lesson video, we're going to talk about our very first one, which is general acid based catalysis. And so acid based catalysis is, of course, when either an acid or a base catalyze is of reaction. And, of course, that's going to occur via a proton transfer or an H plus transfer, since we already know that acids and bases are all about either donating or accepting protons. And so what's important to note is that unstable charged intermediate molecules that form during a reaction can actually be stabilized with proton transfers. And that's exactly why acid based catalysis can be so critical to some reactions. And so let's take a look at our image down below in our example to clear up some of this and so notice that what we have here is a reaction in this box and down below. What we have is the free energy diagram for the same exact reaction that we have up above, and so notice that this reaction of above is actually a two step reaction shown by these two reaction arrows. And so, in the first step of our reaction, noticed that the electron density on this blue oxygen right here is attacking our carbonnel group. And essentially, the electron density that's in the double bond of this Carbonnel group is shifting up onto this red oxygen. And so, ultimately, what that leads to is the formation of this charged intermediate molecule here, where this red oxygen has a negative charge and so recall from up above. We said that sometimes thes charged intermediate molecules that formed during a reaction can actually be unstable. And it turns out that's exactly the case with our charged intermediate molecule here. It's actually unstable, and we can tell from our free energy diagram down below where if we take a look at our charge intermediate molecule notice that it's free energy is actually higher than the free energy of either the reactant or the free energy of the product. And so that's what makes our charged intermediate unstable. And so what I also want you guys to notice here is that notice that the rate of the Ford reaction here or the, um, energy of activation for the Ford reaction to convert the intermediate here into the final product is actually much larger, significantly larger than the energy of activation that's required for the reverse reaction to convert the intermediate backwards back into the reactant and so recall that a smaller energy of activation means that the reaction occurs faster. So what this means is that the backwards reaction here, the reverse reaction shown here actually occurs much faster than the Ford reaction because of the larger energy of activation. And so what this means is that when this intermediate forms, the tendency is for it to break down backwards, right back into the reactant rather than to essentially go forward and be converted into the final product. Which means that our final product is not going to be formed at a substantial rate if the energy of activation for the second step is so large. So we can actually get a MAWR substantial rate of formation for this product if we decrease the energy of activation for this second step of our reaction, and so notice that the second step of our reaction here, indicated by the second arrow, is just a proton transfer or an H plus transfer. And so essentially What's happening is a proton is being transferred to this red oxygen to protein, ate it and stabilize our final product as we can see down below our final product. That stabilized because it has such low free energy. And so what's important to know is that this second step here, this proton transfer can actually be catalyzed by, uh, two main types of acid based ca Tallis. And so the first main type of acid based catalysis is specific acid based catalysis, and so, just like it sounds with specific acid based catalysis Onley, one specific acid or base can serve as the proton transfer source, and that one specific acid or base is going to be the solvent. On Lee, the solvent can serve as the proton transfer source with specific asset based totality. That's why it's so specific and so recall that with biological systems, the solvent is going to be water. And so, with specific acid based catalysis, it's water that's going toe always serve as the proton transfer source, and so as we can see down below, with our non enzymatic reaction that occurs via specific asset based catalysis, which is the black curve in our diagram notice that with specific asset based catalysis sometimes, uh, this can actually just be too slow of a process. And it's slow because noticed that this second step here, the energy of activation again, is much larger then the energy of activation for the reverse reaction to occur. So the Ford reaction is just occurring to slow via specific acid based catalysis, just like we're saying off above. And so what we can do to speed up this second step of our reaction? Here is Thio. Perform our second acid base. CA Tallis is the second main type of acid based catalysis, which is general acid based CA Tallis ISS. And so, just like our sub topic, title tells us this is really the main type of acid based catalysis that we want to focus on in this video. And so general acid based catalysis, just like it sounds like, um is actually pretty general, and that's because it doesn't require a specific acid or base. It actually can occur via any acid or base, and that's why it's so general, because any acid or base conserve as the proton transfer source. However, with general aspects catalysis, the enzyme is actually involved in the process and so we can see that with general acid based cost. Alice ISS The enzymes active site is really what's going to mediate the proton transfer source and because the enzyme is involved, that's going to speed up the reaction and lower the energy of activation. And so we can see that in our energy diagram as well. Notice that the enzyme catalyzed reaction via general acid based catalysis is shown by this green curve right here. And so we can see that the energy of activation here is significantly lowered in comparison to the energy of activation that it was with the non enzymatic reaction. And so what this means is that the product is going to be formed at, ah mawr substantial rate. And so essentially, what we can see here with this second step here, this proton transfer that if, uh the solvent serves as the proton transfer source thing, that means it's going to be specific acid based catalysis because, uh, the water can serve as the proton transfer source and remember, water has the ability to auto ionized and formed this H 30 plus or this hydro knee. Um, I on that can serve as the proton transfer source. And so what helps me remember that, um, specific acid based catalysis is specifically when the solvent serves as the proton transfer source is that I see the s and specific and that reminds me of the S for the solvent. And so, uh, here we can see that the solvent conserve as three proton transfer source. That would be specific acid based catalysis on. So that's why it's black and color coded and black with the energy diagram below. But we know that if the enzyme is mediating the proton transfer source, then uh, it's going to be general acid based catalysis because any acid or base conserve as the proton transfer source. It's just that the enzyme is now mediating this proton transfer. And so that's why it's in green. And we can label it as general for general acid based catalysis, and it's color coded with the green curve down below. And so this here concludes our lesson on the difference between specific and general acid basic analysis, and we'll be able to apply these concepts that we've learned in this video and our practice problems. So I'll see you guys there
Which of the following could not clearly be a contributor to general acid-base catalysis (circle all that apply)?
The catalytic mechanism below is an example of:
General acid catalysis.
Specific acid catalysis.
General base catalysis.
Specific base catalysis.
Which of the following best applies to general acid-base catalysis?
A proton is transferred between the enzyme and substrate.
Uses nucleophilic functional groups.
May take part in interactions involving Fe2+.
Catalyst retains its original form after reaction occurs.
Other than losing/gaining a H+, the catalyst retains its original form.