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Video transcript

- [Voiceover] In the video on competitive inhibition, we saw that competitive inhibition is all about a substrate or a potential substrate, an inhibitor competing for the enzyme. And whoever gets there first, gets the enzyme. If the inhibitor gets there first, then the substrate isn't able to bind, and of course no reaction is catalyzed. If the substrate is able to get there first, then the inhibitor isn't able to bind, and the reaction does get catalyzed. Now the inhibitor and the substrate, they both might compete for the active site, if we're talking about competitive inhibition. But you also have allosteric competitive inhibition. Where they're still trying to compete for the enzyme, whoever gets there first, gets the enzyme. But the inhibitor doesn't necessarily bind at the active site, they bind at an allosteric site. But it's the same idea. If the inhibitor gets to the allosteric site before the substrate gets to the active site, then the confirmation of the protein changes, so that the active site, you know it changes a little bit, something like let me draw in that same color, the confirmation of the protein changes a little bit. And then the actual intended substrate isn't able to bind. If the intended substrate binds, then that changes the confirmation a little bit at the allosteric site, and then the inhibitor isn't able to bind. So if that's competitive inhibition, where there's like who gets to the enzyme first, what is non-competitive inhibition all about? Well let's draw that. So, non-competitive inhibition. So, non-competitive inhibition. And the big picture here is that they can both bind. Whether one binds to the enzyme doesn't affect whether the other binds. So let's talk about it a little bit. So, this is my enzyme. That's my enzyme, right over there. And what we have happening, of course, is if the substrate's able to get to the active site, then of course the reaction is going to be catalyzed. And we saw that up here. Substrate binds to the active site, and then the reaction is catalyzed, in this case the substrate got broken up into two other molecules. But in non-competitive inhibition, what happens is a substrate can bind, and so can an inhibitor. And the inhibitor can bind at an allosteric site, so this is our inhibitor right over here. The inhibitor can bind at an allosteric site, and when they're both bound, notice they're not competing for the enzyme, they both can be on the enzyme. This character can bind to the enzyme whether or not the substrate is there. But if this guy binds to the enzyme, the substrate can still bind to the enzyme, but now the reaction isn't going to proceed. So now the reaction is going to look like this: so now there's not going to be a reaction. If this happens, the only option is that they both unbind. So now this character is just going to leave the active site. No reaction has been catalyzed. So, it just prevented anything from happening. And maybe this guy leaves as well. And the way I showed this non-competitive inhibition, I showed it happening at an allosteric site, the inhibitor attaching at an allosteric site, but it actually doesn't even have to be the same case as long as it does not prevent, it can actually bind close to or even at the active site as long as it does not prevent the substrate from binding to the active site. So you can even have a situation like this: this is the one that's typically given for non-competitive inhibition where you have the inhibitor binding at an allosteric site, but the idea here is that both of them can bind to the enzyme. If one of them binds first, then the other one can still bind. If the substrate binds first, then the inhibitor can still bind. If the inhibitor binds first, then the substrate can still bind. But, the reaction is not going to be catalyzed. But you can even have a situation where the inhibitor and the substrate can both bind in or around the active site. So that's the inhibitor, and then this is our substrate, this is the substrate. But once again, this reaction is not going to occur. We have non-competitive inhibition. They're not competing for the thing, they can both bind to it, whether they can bind isn't dependent on whether the other one is bound, but if the inhibitor is there then it's not going to allow the reaction to actually be catalyzed. As opposed to competitive inhibition, whoever gets to the enzyme first, gets the enzyme. Hopefully that clarifies things.
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