Competitive inhibition

we've already seen that an enzyme helps catalyze a reaction so let's say this right over here this is our enzyme and we have our substrate and it goes and it binds to the active site to the active site of the enzyme so let's say it binds right over there so that's site on that on the enzyme we call the active site where the substrate binds and then the enzyme catalyzes reaction maybe it breaks up the substrate into two smaller molecules and so after the reaction after the reaction we the enzyme whoops after the reaction the enzyme is unchanged but a reaction has been catalyzed we now have we now have the substrate being broken up in this case at least into two smaller molecules maybe I'll draw them that's one of them and this is the other one right over here so they just came they just came from the active site once the once the reaction is catalyzed they don't they don't have the affinity to the active site anymore and they break off so this enzyme has just catalyzed this reaction what I want to talk about in this video is how this might be inhibited and and specifically how it might be inhibited competitively so we're going to talk about competitive inhibition so competitive let me write it over here competitive competitive inhibition in hish case of competitive inhibition if there's some if there's some molecule that competes for the substrate at the active site as we'll see this isn't the only form of competitive inhibition but this is the the one that you will most typically see in a textbook so let's do so that's our enzyme again and so that's our enzyme and we've already seen that this is an act this is right over here where I'm circling that is the active site active active site and if the molecule the intended substrate in case you could say gets to it we're going to have this first scenario up here but in classic competitive inhibition or at least the version I'm just going to show you right now you could have another molecule you could have another molecule that let's say it looks something like this that can compete for the active site and if it gets and if it gets to the active site first so if it gets there first so let me show what's going to happen so then we have our enzyme we have the other molecule not the intended substrate binds to the active site first well now the intended substrate the one for which the enzyme catalyzed reaction isn't able to bind and the reaction isn't going to happen and you can see very clear that they are competing for the enzyme in there in this case they're competing for the active site now this isn't the only form of competitive inhibition another form of competitive inhibition is allosteric competitive inhibition let me write this down so you have allosteric allô steric competitive competitive inhibition in I'm having trouble writing inhibition and an allosteric site is a site other than the active site but in competitive in allosteric competitive inhibition or competitive allosteric inhibition however you want to say it you have a scenario where the competitor the competitor doesn't bind to the active site but binds to a site that is not the active site and now we'll steric site we could say so in that one the competitor maybe might bind here so that's clearly not the active site so maybe the competitor looks something like that it didn't bind to the active site but by binding there the active site is no longer it can no longer bind to the intended substrate so you have the same effect you have the same effect right over here where this thing isn't going to bind but if this thing binds first so let me draw that scenario so if the intended substrate binds first then the competitor can't bind so in this scenario if the substrate is able to get to the active site well then the competitor can bind so once again they're competing so I'll draw the competitor here so then the competitor whoever gets to it first gets the enzyme so in this situation the competitor is not going to bind so that's true of whether you're talking about competitive inhibition where they're competing for the active site if the competitor gets there first the intended substrate isn't going to get there and the the reaction isn't going to be catalyzed if or if or if the intended substrate gets first then the competitor is not going to be able to get there in fact it could have been this situation where because the substrate got there first the competitor the competitor isn't going to be able to bind to the active site we're talk about allosteric competitive inhibition we're still competing for the enzyme only ones going to get it if one gets to the enzyme first then the other ones not going to be able to get there they are competing for the enzyme but the competitor the non substrate is just acting in an allosteric site by binding to an allosteric site it changes the conformation of the enzyme so that the active site no longer binds to the substrate and I want to really emphasize this point because when I first learned this I said oh it's often sometimes confused and even some things you'll read on the internet that they'll say that this is that this allosteric type of inhibition they'll call this non-competitive because you're not competing for the active site but that is actually not the case in non-competitive inhibition and I'm going to do the whole next video on non-competitive inhibition and non-competitive inhibition the the inhibitor the inhibitor right over here can bind regardless of whether the substrate has bound or not but when the inhibitor does bind it prevents the reaction from moving forward it changes the the conformation of the protein so it no longer catalyzes the reaction so non-competitive they both can bind but if the inhibitor is there the reaction isn't going to proceed in competitive inhibition whether we're talking about allosteric or non allosteric competitive inhibition only only one of the substrate or the inhibitor is going to be able to bind they're competing for the enzyme