in this video we're going to look at how temperature and pH affect the functioning of enzymes and therefore the rate of enzyme controlled reactions let's start with temperature this graph here shows how the rate of an enzyme controlled reaction changes with temperature as you can see for the first part of the curve as the temperature increases so does the rate of reaction and this is because all of the particles will have more kinetic energy and so they're more likely to collide and have enough energy to react after about 37° though the rate starts to drop rapidly this is because the high temperatures start to break some of the bonds holding the enzymes together and so the active site starts to change shape if it changes shape enough then the enzyme won't be able to bind to the substrate and catalyze the reaction anymore and at that point we say that the enzyme has been denatured so in this case the enzyme would become denatured at around 45° and at that point the damage is permanent so even if you lower the temperature back down the enzyme won't start working again another important term to know is the optimum temperature which is this temperature here at which the rate of reaction is highest so in this case that would be 37° all enzymes have an optimal temperature but different enzymes will have different optimal temperatures the other factor that can affect enzymes is pH pH is a measure of acidity and as you can see on this graph here if the pH gets to high or too low then it will lower the rate of reaction just like with temperatures this is because some of the bonds holding the enzyme together start to break and so the active site starts to change shape at first it just changes a bit so the substrate can still fit but less well than normal this slows down the rate of reaction but doesn't completely stop it soon though the active site changes shape so much that the substrate can't fit at all and at this point we'd say that the enzyme has been denatured the pH at which the enzyme works best is called its optimal pH and it depends on where the enzyme normally works for example most enzymes in our body work best at neutral phes of around seven like in this graph but the ones that work in the stomach for example have an optimal pH of around two because they need to be able to function in the stomach's acidic environment hey everyone amadas here I just wanted to let you know that we also have a learning platform where you can watch all of our videos practice what you've learned with questions and keep track of all of your progress for both The Sciences and maths so if you haven't already you can check it out by clicking on our logo here on the right or if you'd like to do the lesson for this particular video we put the link to that in the description down below we've also arranged all the videos for this subject in a playlist for you here that's all though so hope you enjoy and we'll see you next time thanks