so with all this talks about uh enzymes which are obviously very important we've talked about the active site and their other groups would it not be useful if we were able to see how enzymes are working in real time the problem is we can't really see how enzymes move we can't really see how enzymes are reacting with substrates using our eyes for the very simple reasons that enzymes are extremely small um and even with the best microscopes in the world remember if you have an electron microscope um you would we would not be able to see enzymes because again too small and even if you could see an enzyme um electron microscopes can show movements so you'll just get a still image you can't see how enzymes are reacting with the substrates uh so if we can't see how enzymes move and work and react with substrates what do we do then so we try to describe their functionality using something called models and a model is just not not we're not talking supermodels here we're just basically using a model is just an analogy of a comparison used as an example okay so uh to to try to convey a rather uh difficult idea we try to use two ways to describe how enzymes work the first model is using something known as the lock-in key model and the second model is the induced fit model so let's not waste time and let's immediately go into the lock and key model the lock and key model basically is trying to equate the enzyme and the substrate to a lock and key just like how a lock has a specific key required to open it the enzyme is specific to a substrate due to their shapes due to their complementary shapes so the enzymes active site is highly specific to the substrate or complementary to the substrate I've mentioned before in the previous video that students sometimes make the mistakes and they say that the enzymes active site has the same shape as the substrate that is wrong by the way the enzymes active site actually is highly specific and complementary or matching to the substrate they don't have the same shape that's a very important thing to understand so for example if I'm just representing the enzyme here in this purple color uh this purple color structure this is an enzyme and as we can see a substrate a substrate is just something that reacts with the enzyme and as you can see the active site of the enzyme which I'm highlighted okay is complementary to the bond within the substrate which I've also highlighted so the highlighted regions are actually highly specific complementary or matching now because they are matching they are able to then bind to each other and form something called the enzyme substrate complex if you remember in the previous video the enzyme substate complex forms because of the interaction of the r groups in the enzymes active site and the substrate it's just a temporary linkage by the way temporary meaning to say it's not forever it's just for a while for a reaction to happen so that the other groups can weaken the bonds so it makes it easier it reduces the activation energy required for the reaction to happen and once it's reduced the activation energy in this case it will the high voltage successfully happens if this enzyme is a hydrologic enzyme and the substrate is now converted into products that's essentially what happens and look at the enzyme the enzyme is basically unaffected and the enzyme can be reusable in this situation now the problem is what if there's another type of substrate trying to react with this enzyme would they be able to react with each other now based on the lock and key model no it will not be able to react with each other the reason is because the shape of the substrate is not complementary to the active side of the enzyme so it cannot form the enzyme substrate complex no reactions can take place in this situation therefore nothing happens but here's where there's another type of model used to describe how enzymes function and this second model over here is the induced fit model now the indiosphate model states that the active site is not rigid the active side of the enzyme is flexible now what do I mean by flexible imagine an enzyme where I'm just highlighting with the substrate okay now based on just this diagram here will they be able to form the es complex yes they will be able to form the es complex the reason why they are able to form the as complex is because the shape of the substrate is complementary to the active side of the enzyme so they can form the es complex but what if I were to draw out another substrate now in this situation here will it then be able to react with the enzyme if you were following the lock and key model the lock and key model says no it can't because the the shape is not matching but the induce fit model is trying to tell us that some enzymes not all but some enzymes have a rather flexible shape so even though at first they were not complementary but what may happen is the active site is malleable and the active site changes its shape to fit the substrate on the active side changes slightly to fit the substrate and therefore it still is able to form the enzyme subset complex so this is what is meant by the active side is flexible so the active size shape is not just in one fixed position it is actually able to mold itself to the shape of the substrate reduce the activation energy and catalyze the chemical reaction that needs to happen and once the substrate in this case has been broken down into products and detaches from the enzyme look at the active site the active site returns back to its original position so the beauty of the Indus fit model is that this enzyme was able to react with two types of substrates so in the login key model the login key model here just basically says that the active site is fixed and it only matches one specific substrate and based on my diagram here even though there are two substrates over here it's only the substrate on the left that can actually bond with the enzyme the substrate on the right is unable to do so but in the induce fit model however both substrates are actually able to react with the enzyme because the enzymes active site is able to fit are able to change its shape to match with whatever substrate that reacts with it so by comparison the actives for the lock and key model the active site is rigid and fixed but for the enzyme in the induced fit model the active site is more flexible so of course some students will ask them okay um fine I get this point but then which model does the enzyme follow does the enzyme follow the lock and key model does the enzyme follow the induce fit model on his answer it can be both by the way some enzymes May subscribe to the lock and key some enzymes may prefer to do induced with it really depends on the situation it really depends on the type of enzymes as students do you have to know which enzymes do lock and key and which enzymes do they induce fit no you don't you just have to know what it stands for and what's the difference between the two models and there are some similarities too between the two models what are the similarities the similarities between the two models are they are able when they are able to react with the substrate they are able to form the enzyme substrate complex they lower the activation energy required for the chemical reactions to happen and once they convert the substrate into products the enzymes are then reusable no matter what the model is