hello and welcome to learn a level biology for free with miss estrich in this video i'm going through the factors which are affecting enzyme action so there are different factors that are going to affect the enzyme and affect them in different ways some of them are going to be to do with the rate of reaction because of the protein structure changing others are slightly different and the reason that the protein structure can change is proteins are sensitive to different conditions because of the bonds which hold them together in their tertiary structure so that's what we'll be focusing on so condition number one is temperature and if the temperature is too low so if the substrate or the enzymes have too lower temperature then there's not going to be enough kinetic energy for them to be moving fast enough to have successful collisions between that enzyme active sites and the substrate so therefore you end up with fewer enzyme substrate complexes and that's why we can see the rate is lower at these cooler temperatures if the temperature goes beyond the optimum though you then have too much kinetic energy and the enzyme denatures and what we mean by that is the active site has changed shape and again if it's changed shape this time you won't get any enzyme substrate complexes so the reason it denatures if there's too much kinetic energy is the bonds holding the amino acids in their fixed 3d tertiary structure in the active site are going to be broken because of that increase in temperature ph is our second condition and if you have too high or too low a ph then the enzyme will denature in this case and that's because if it's too high a ph you have too many hydrogen ions if it's too low a ph you'll have too many oh minus ions and both of those because they have either a positive or negative charge they interfere with the charges in the amino acids within that active site and again the result of that is the bonds holding those amino acids together in their 3d shape will break and that's mainly the ionic and hydrogen bonds will break and that means your active site slightly changes shape and therefore the enzyme has denatured when an enzyme is denatured we end up with fewer enzyme substrate complexes and that's why the rate of reaction is lower now although in this graph it's showing the optimal ph is ph 7 different enzymes do have different optimal phs amylase for example is slightly alkaline its optimum whereas proteases will have very acidic optimums and it all depends on where that enzyme is naturally occurring so next then it's looking at substrate and enzyme concentration and how these two variables affect the rate of reaction now they both have a very similar effect and it's to do with the successful collisions between the enzyme and the substrate so if we have a look at substrate concentration first at low substrate concentrations there is a lower rate of reaction and we have this positive correlation up to a certain concentration and that indicates that at low concentrations of substrate the substrate concentration is the limiting factor the reason for that is if there is insufficient substrate the reaction is slower because there's fewer substrate molecules available to collide with the enzyme so you end up with fewer enzyme substrate complexes and therefore the rate of reaction is slower but we do then see this plateau and at that stage when you increase the substrate concentration the rate of reaction remains constant and that's because it's now a new limiting factor and it is the enzyme concentration so when you add more and more substrates eventually if you aren't also adding more enzyme the active sites will become fully saturated so every single sat every single active site is already used in use and therefore the reaction cannot occur any faster the enzyme concentration graph again we see that same pattern that low enzyme concentrations that is the limiting factor because we see this positive correlation as you increase the enzyme concentration the rate of reaction also increases and that's because if you have insufficient enzymes then the enzyme active sites will become saturated with very very little substrate and therefore you again have a slower rate of reaction because there's no more active sites available for the reaction so when you get to a higher enzyme concentration again we see the rate of reaction plateaus it levels off and that's because there's a new limiting factor and at this stage we now have empty active sites and that's because we now have far more enzymes than we do substrates so some of those enzymes at the high concentration are just not in use because there's not enough substrate to collide successfully with their active sites so in both of these examples unless you were to have a sufficient amount of enzyme and substrate you will see a plateau now if you did have an indefinite supply of both you would see a directly proportional line on your graph so this positive correlation indefinitely if you continually added more substrate and more enzyme so the last thing is inhibitors and this is new from gcse you wouldn't have learned inhibitors at that stage and there are two inhibitors competitive and non-competitive inhibitors and in general what we mean by an inhibitor is it's a molecule which binds somewhere on the enzyme and therefore it prevents the enzyme from functioning a competitive inhibitor is when the molecule is the same shape as the substrate or it might be very very similar in shape but not identical and therefore is also complementary in shape to the active site it's able to bind and we now get what's called an enzyme inhibitor complex and that prevents the substrate from being able to bind and therefore you won't be getting any enzyme substrate complexes and the reaction isn't occurring or be much much slower so that is how the competitive inhibitor works however if you do add very high concentrations of the substrate that can flood out the inhibitor so it can knock the inhibitor out of the active site therefore the substrate can then collide successfully and bind and the rate of reaction should then match that of a non-inhibitor rate of reaction in contrast the non-competitive inhibitors again it's an inhibitor so it binds to the enzyme but it binds away from the active site and it can bind at any location that it's complementary to that is not the active site now the technical name for that is the allosteric sites but that's not on the specification that you have to know that term you do just need to know that non-competitive inhibitors bind to the enzyme away from the active sites and the impact that that has is when that inhibitor binds it slightly changes the tertiary structure which is that unique 3d shape and therefore the active site slightly changes shape and because the active site is now a different shape the substrate is no longer complementary in shape to that active site and therefore even if it does collide it's not going to bind to form an enzyme substrate complex so that is how the non-competitive inhibitors prevent the substrate from binding and therefore prevent um that faster rate of reaction so just to show you how that could be linked to a graph in an exam question and it's this graph here at the bottom quite a common question is you're shown the rate of reaction for this particular enzyme controlled reaction with substrate concentration against rate of reaction and is shown for a the reaction with no inhibitor at all which i've shown here in the blue line now you could be asked to draw on the line for the competitive inhibitor and the non-competitive inhibitor and there's two key things that they'll be looking for for the competitive inhibitor so for the line for a competitive inhibitor the rate of reaction is lower than that of the reaction without an inhibit inhibitor until you get to very high substrate concentrations because at that stage there's now so much substrate it out computes the inhibitor knocks them out and then the substrate combined and the rate of reaction returns to normal so they'll be looking for the fact that your line is lower but then it does meet the same endpoint in terms of rate of reaction the non-competitive inhibitor though this one will have a lower rate of reaction but it plateaus it levels off at a much much lower rate of reaction and that's because even when you do add more and more substrate it does not knock out the inhibitor the active site is a different shape so therefore it's no longer catalyzing the reaction and you reach your maximum rate of reaction and it's a much much lower rate so that is your two competitive inhibitors um knowing the theory of how they work but also being able to demonstrate that on a graph so that is it for the factors which are affecting enzymes [Music] you