so what we have to talk about today is the topic on enzyme inhibitors by definition enzyme Inhibitors are any molecules that prevents enzymes from functioning at an Optimum rate you don't have to memorize that definition but what the word Inhibitors mean in this case is to stop or to reduce or to block the enzymes from functioning so remember just a little bit of revision enzymes are referred to as globular proteins because they usually are water soluble and they have a 3D spherical or bowl shaped and in this case I'm just throwing out a simple enzyme here you can see the 3D structure where the polypeptide chain is coiled and I'm drawing out the outline of the enzyme now when you bring up the outline of the enzyme you can see two very specific areas where there is an inward folding or a depression of the surface of the enzyme okay now one of the inward folding is referred to as the active site and the active site you know is very important because it is complementary to a particular substrate it will bind to the substrate using the r groups form something called the es complex and reduce the activation energy needed for the chemical reaction to happen we've studied this in previous videos uh but there is a slightly different shape on the other side which is referred to as the allosteric site the allostatic side you don't have to remember that term you don't have to memorize it it's good to be familiar with what that site is it is just a site of the enzyme that is not the active site so then you might be thinking so if that is not the active site uh what function does it have so we will talk about this in a while but what we have to be aware of is right now the enzyme can have two sides one site where it's complementary to the substrate referred to as the active site and one side that is not complementary to be substrate and some books will refer to it as the allosteric site so what does this have to do with Inhibitors you see the first type of inhibitor we are going to be looking at is something known as competitive Inhibitors the key word here is competitive which means to say this Inhibitors are going to be fighting that is why the definition is any substance that competes with substrates so you might be thinking what are they fighting with the substrates then because substrates are some things that bind to the active side so competitive Inhibitors are also molecules that can also bind to the active site of the enzyme if I illustrate an enzyme here I'm not going to draw the allostatic side okay because I just want to keep it as simple as possible so you see an enzyme and the highlighted region of the enzyme is the active site like a mouth and the substrate which is green in color is complementary to the active site so in this case this is good so they can form something known as an es complex however what might happen here is another molecule can also exist and that molecule is referred to as a competitive inhibitor now look at the shape of the competitive inhibitor and the substrate their shapes are not exactly the same the substrate looks like a pie shape and the competitive inhibitor just looks like a small Arch if you can just like a small bent um structure if you may but here what may actually happen is the competitive inhibitor is still complementary to the active site where it can match with the active side of the enzyme and block it and when it blocks the active site this substrate is no longer able to enter the active site and therefore it cannot form the e as complex so no reduction of activation energy takes place with the substrate and the substrate cannot be converted into products so in this case a chemical reaction will not happen that is what is meant as enzyme Inhibitors the competitive inhibitor in this case prevents the enzyme from binding to the substrate and therefore no chemical reaction takes place and a lot of times students will then ask me the question oh so if the competitive inhibitor binds to the active site will anything happen to that molecule nothing will happen to the competitive inhibitor it does not react with the enzyme it merely blocks the active site and when it blocks the active site the substrates cannot bind to them any longer that's it now for your level you just have to know that the inhibition is reversible what it means by this is the competitive inhibitor will not permanently attach to the active site after a short period of time it will detach from the active site so it just binds to the active site for a while then goes out of it there are some competitive Inhibitors which are permanent but you do not need to know them for your a-level syllabus you just have to know that these competitive Inhibitors are temporary or reversible then I'll ask my students a question are competitive enzyme inhibitors bad so a lot of times students will say yeah they are bad because they are preventing the enzymes from functioning and if the enzymes cannot function no chemical reactions can take place so here's the interesting thing in theory competitive inhibition might sound bad and in some cases they can actually be detrimental to our body that is true however there are certain specific situations where competitive inhibition is actually pretty good it's something that is not bad to happen now I don't need you to memorize this particular situation this is just for your own understanding as to why competitive inhibition can be good so imagine a particular substance referred to as an antifreeze you can Google what antifreeze is but antifreeze is a particular chemical that prevents liquid from freezing we use this a lot in machines that require water to move in very low temperature sometimes in very large refrigerating components even air conditioning also has antifreeze as well now the thing about antifreeze is it has a very sweet smell and it has a kind of colorful when you pour antifreeze on the floor when it catches the light it has a kind of rainbow Spectrum effect that appears on it so it looks kind of beautiful but antifreeze is quite poisonous so imagine antifreeze and it has a particular uh chemical in the antifreeze which is triangular shape okay just imagine it like that now for some reason people will try to drink antifreeze please do not drink antifreeze it is not healthy or safe to drink antifreeze you can uh cause a lot of damage to your body when you drink something that is potentially toxic to your body what happens is your liver is an organ that will break down the antifreeze and how it breaks down the antifreezes there's a particular enzyme inside the liver that takes the antifreeze molecule so you can see the antifreeze binding to it and it breaks it down into a particular product and the name of the product is called oxalic acid so you might be thinking oh this is good because your liver is breaking down antifreeze which is a toxic component and it breaks it down into a product now this is actually quite bad because when you have too much oxalic acid in your body which is a product too much of this particular product can damage your kidneys permanently that is why I told you please do not drink antifreeze it is not something that is for human consumption so in this case here then what actually happens here is the reaction we do not want this reaction to happen we do not want the liver enzymes to break down the antifreeze and convert it into oxalic acid in fact we want to prevent it from happening because the products can actually damage our kidneys what doctors will do is when a person comes to the hospital with antifreeze poisoning doctors will actually give the patients ethanol so why ethanol because ethanol is a competitive inhibitor and when the competitive inhibitor binds to the active site as you can see here the ethanol has attached to the active side of the liver enzymes so the antifreeze which is the substrate can no longer bind to the liver enzyme so no es complex formation no antifreeze will be broken down and no oxalic acid is formed therefore no kidney damage takes place this is an example of a good competitive inhibitor I'm not saying that all competitive Inhibitors are good but here's an interesting case where sometimes preventing the enzymes from functioning is actually a good thing this is just a situation in which competitive inhibition can be beneficial for our body however you do not need to memorize this for the exam I just like talking about it so coming back to how competitive Inhibitors can affect the weight of reaction I'm just putting out the guide at the top the green colored triangular substance are substrates the orange pigments are enzymes and the blue color curved molecule is a competitive inhibitor now imagine for a while we have a situation where we want to see how substrate concentration affects the initial rate of reaction so I have two experiments over here the experiment on the left is without competitive Inhibitors and the experiment on the right is with competitive Inhibitors now imagine for a while if I get two percent substrates in both cases so in the first case over here on the left the substrate can bind to two enzymes so in this case we will say that two enzymes are occupied by the substrate so the initial weight of reaction is two which I've plot in the graph and for the one on the right I have two percent substrates as well but I also have some competitive inhibitor what might happen here is the competitive inhibitor might attach to four of the enzymes so even though I have two percent substrates only one substrate can bind to the enzyme and in this case over here the initial weight of reaction will be lower so you see competitive Inhibitors actually lower the initial weight of reaction as you can see in the graph what if I were to add four percent substrates in four percent substrates on the left four of them can bind to the enzymes so the initial weight of reaction in this case is four plot that in the graph now on the right four percent of substrates okay here's where it becomes interesting when you have more substrates or when you have a higher concentration of substrates there will be a higher chance to bind to the active site so in this case imagine then three of the competitive Inhibitors can attach to the active site but because you have more substrates and they are fighting with the Inhibitors two of them can kind of like you know uh push away the competitive inhibitor so in this case at least two substrates were able to bind to the active site so I'm just going to plot that into the graph as well imagine now if I put five percent substrates and all five of them can bind to the enzyme and if I were to put six percent substrate remember how many substrates can bind to the enzyme still only five of them can bind to the enzyme because there are only five enzymes available so in this case we say that a V Max value has been reached if you remember V Max V Max just tells us that uh there is a limited concentration of enzymes available for the initial weight of reaction so let's look at competitive Inhibitors if I were to add five percent substrates into this particular experiment more chances of the substrates to bind to the active sites happen because when you have more substrates they can kind of push away the competitive Inhibitors in in order to bind to the enzymes and if I were to add 10 Subspace in this case look there is an extremely high concentration of substrates in this case so in this situation will there be any chance for the competitive inhibitor to bind to this enzymes in my diagram here no because the competitive Inhibitors are hidden away so the substrates will have a high chance of binding to the enzymes and thus in this case you are able to reach a value of V Max without competitive Inhibitors you reach the Vmax value much earlier but with competitive Inhibitors the V Max value is reached much later at a higher concentration of substrates that is what you have to know about the pattern of this graph so with competitive Inhibitors you can still reach the Vmax but it requires a higher concentration of substrates if you are not so sure about this let's look at this in detail again okay I just I just want to make sure that you understand this so I have two situations here one experiment without competitive Inhibitors one experiment with competitive Inhibitors when it's without competitive Inhibitors theoretically five percent of substrates will bind to all five active sites and will I reach Vmax in this case yes I will reach Vmax in this situation but with competitive inhibitor and I have five percent of substrate will all five of them bind to the active site no because competitive Inhibitors also have a chance to do so so did it reach Vmax in this case it did not reach Vmax because only three enzymes are occupied by the substrates if I want the experiment on the right to reach Vmax what do I have to do so that you might say oh I have to add more substrates or have to increase the concentration of substrates so let's increase the Subspace to let's say about 10 so with 10 substrates here can I reach Vmax yes I can reach Vmax in this situation because the competitive Inhibitors do not have a chance to bind to the active site of the enzyme that is what I told you earlier that without competitive Inhibitors you can reach the Vmax much earlier in this case five percent but with competitive Inhibitors the Vmax is reached much later at a higher concentration of substrates so if a question asks you I want to reduce the chances of the competitive Inhibitors from binding to the enzymes how do I do so in order to do so you have to increase the concentration of substrates that's what it means this is what we have to know about competitive Inhibitors in a nutshell