this is the video for the standard level content from C 1.1 on enzymes and Metabolism enzymes are example of what we call a catalyst and a catalyst is anything that increases the rate of a chemical reaction or makes it faster and catalysts are not consumed in a reaction so enzymes are protein-based biological catalyst so they are proteins that help speed up reactions now in chemical reactions we have reactants and they get transformed into products the reactants in an enzyme catalyzed reaction are called substrates so this word substrate means the same thing as reactant it's just a special way of saying reactant for a reaction that involves an enzyme so why do we have enzymes and why are enzymes so important well all of these reactions that take place in our cells would normally occur but they would occur much too slowly in order to sustain life or we would need to raise the temperature up so much to get those reactions going that we wouldn't be able to sustain life so enzymes make it possible to have all of those cellular reactions at a temperature that's amendable for life and a speed one term that we'll talk about quite a bit um throughout this topic is metabolism and a lot of students make the mistake of thinking that metabolism is how many calories that you burn well in biology we use that term a bit differently so we'll Define metabolism as the sum of all of the enzyme catalyzed reactions in our cells and metabolic reactions can look like a variety of things they can either be chains okay or they could be Cycles okay we'll talk about examples of each but they can look very different from each other um and enzymes are NE necessary for every single one of them now enzymes are substrate specific so that means that each substrate in each reaction needs its own enzyme so if we have lots of different metabolic reactions that also means that we need lots of different enzymes okay so again one of the reasons that we have enzymes is to speed up this reactions but also it offers cells a method of control so a way of controlling which metabolic reactions need to take place and when one of the ways to categorize all of the metabolic reactions is to say that they are either anabolic or catabolic so let's just quickly talk about these I like to think about catabolic first catabolic reminds me of catastrophe things falling apart so that would be something more like this going from one large molecule and breaking it down into several small small components so here we're going from some kind of big molecule into a bunch of smaller molecules and this is going to involve breaking bonds okay so I'm taking bonds apart and to do this we use hydrolysis reaction so those are the reactions where you add in water to break molecules apart and this in general is going to release energy okay so there is energy contained within the bonds between um bits of molecules and when you break that Bond you release that energy so one of the examples here classic examples of a catabolic reaction is cell respiration now I'm totally um generalizing there cell respiration is many many reactions but in general cell respiration is going to be taking apart something like glucose and utilizing that energy from the breaking of bonds now if we want to think about the opposite okay then we can get into anabolic reactions anabolic reactions are going to be going the other way like this okay so like if you think about anabolic steroids those are for like building muscles and here I'm going to be building molecules so I'm going to be taking smaller molecules and I'm going to be putting them together into a big molecule or a bigger molecule and this involves not breaking bonds but making bonds or forming bonds and to do this we use those condensation reactions so the condensation reactions are opposite of hydrolysis um I would be removing water in order to form a bond and forming bonds requires energy all right so I need to be thinking about a process where I'm going to be ending up with a bigger molecule than than when I started and I need to put in energy so a great example here is photosynthesis okay so just like with cell respiration photosynthesis is actually many reactions put together but overall it's anabolic using energy in this case from light to create a molecule that is bigger like glucose by forming bonds now those anabolic and catabolic reactions um Can Be catalyzed by enzymes so let's dive deeper and what an enzyme actually looks like it is a globular protein okay so globular that means it's three-dimensional in shape that means it's soluble and it's going to be folded into a very very specific shape okay and this shape is determined by the amino acid sequence which is of course determined by the DNA sequence okay so all these enzymes have a specific DNA code they make a specific amino acid sequence that folds into a specific shaped protein somewhere along that enzyme surface we'll find a special spot called an active site and this active site is going to be where the substrate binds okay so it'll be some very very highly specifically um folded uh region of this enzyme and it will be folded in a way that allows its substrate to bind so the active site is actually part of the enzyme um where the substrate will bind it will of course have a shape that is complementary to the substrate because remember those enzymes are specific to their substrates throughout history there have been several models proposed for how enzymes interact with those substrates we used to talk about a lock and a key how they were like very complimentary in a fixed shape the most recent and best supported hypothesis is something called the induced fit model and this still still means that the enzyme is still substrate specific so for example the enzyme lactase can only work on the substrate called lactose but the active sight is not a fixed shape the active site will actually mold and change when the substrate binds and so it looks a little something like this the substrate will bind to the active site on the enzyme and when that happens we get what's called a confirmational change and that means that protein the enzyme the active site actually changes shape ever so slightly when it changes shape that affects the bonding between the substrates so it can actually like weaken bonds or put things in a different orientation and it's that changing of the shape and altering of the bonding that allows the enzyme to catalyze that reaction so at that point the product is released and the active site goes goes back to its original shape so there's a couple important things to point out here it is still substrate specific just because it changes shape doesn't mean it can change shape to work on lots of different substrates that's not what's happening okay it does change the shape to help catalyze that reaction and alter the bonding in the substrates the last thing I want to point out here is that that enzyme is not consumed in the reaction it isn't used up it goes back to its original state which is why enzymes can be used over and over and over again without being consumed in the reaction now in order for chemical reactions to take place we need two molecules to collide okay and when we think about successful chemical reactions those collisions have to cover two basic principles so they have to have enough energy when they Collide and that energy can be um influenced by temperature right because hotter molecules or things at a higher temperature those molecules are moving faster so they have more energy okay or concentration right so that concentration is going to increase how frequently those molecules Collide if it's really crowded in there they're going to collide more often we also have to think about the orientation that those molecules are colliding in so in order for two molecules to react they need to collide at the correct orientation if they Collide in a different orientation no chemical reaction takes place okay so this is also true of the active site of an enzyme in order for a substrate to interact with an enzyme they must collide with the correct orientation now there are a couple of different options for how these enzymes and substrates might Collide you can have a situation like with DNA replic application where the substrate stays stationary and the enzyme moves so the enzyme goes to the substrate or like with ATP synthes which is an enzyme that we use in cell respiration the enzyme can stay in one place and the substrate moves okay or more likely you can have an enzyme and substrate both moving and so it's important to remember that the enzyme and the substrate in most cases are dissolved in solution and that cytoplasm so they both have the ability to move around and collide with each other now not only must the enzyme and the substrate Collide but it has to be the right enzyme with the right substrate they are substrate specific and so that can mean either one exact molecule or an exact molecule or several closely related molecules that are all going to have a very very similar shape that relies on the active site being exactly how it needs to be in order for that sub subrate to bind there is however a process called denaturation that causes a permanent change to that three-dimensional shape of the enzyme so I can see this here that the the active site is specifically shaped for the substrate if something happens and that active site changes its shape okay then that substrate will no longer be able to bind and I have permanently caused this enzyme to be unable to catalyze this reaction okay so that changing of the active site is a process known as denaturation and there are a couple of things that can cause that so we're going to look at the effects of three different um factors on enzyme activity so we'll start off here with temperature if ever you're trying to sketch these graphs on an exam it's important that you have the um Factor at the bottom and then a way of of measuring the enzyme here so I have this as reaction rate if you're looking at a particular reaction you could be more specific rate of oxygen production or something like that okay so we're going to take a look at the effect of reaction rate on temperature and as reactions increase in temperature the rate is going to go up and up and up and up and up kind of in this linear fashion and it's not really anything to do with the enzyme this is just because molecules are moving faster and when molecules move faster they have more energy when they Collide and the reate of the reaction is going to increase now that's going to increase up to a certain point okay and then at this point here we're going to see a very sharp decline so notice that this is not symmetrical here so when I'm looking at this graph I can see that this temperature here when it's at is its Optimum rate or its fastest rate this is what we call the optimum temperature and that means that is the temperature at which the rea the enzyme is working at its maximum rate that will be different for every enzyme okay different enzymes have different Optimum temperatures and so what's happening on either side of this graph is that on the front side here right as the temperature increases those molecules are moving faster and faster and faster and then we get to our optimal temperature right working at maximum speed and then after that th after you increase the temperature further okay so these warmer temperatures that enzyme has been denatured okay so that enzyme is no longer able to catalyze that reaction and I'm going to see a very sharp decline in rate of reaction for pH I'm going to see much more of a symmetrical curve okay so I still have this point at the tippy top where at a certain pH my enzyme is working um at its maximum rate and this is of course the optimum pH different enzymes have a different optimum pH so your enzymes necessary for digesting proteins in your stomach are going to need a different pH than enzymes in your small intestine let's say okay now on either side of this what we're getting um in these really acidic pH or can see really acidic but more acidic than that enzyme cares to be in or more basic than that enzyme cares to be in we'll find that that enzyme has been denatured so that's happening on both sides of the graph so anytime you take an enzyme out of its optimal pH it's going to denature and so that's very different than the temperature where we're only getting denaturation happening in uh temperatures that are hotter than optimal pH and the last factor that we'll take a look at is substrate concentration so this is how many of those substrate molecules can I pack into a small area so as that substrate concentration increases so does the rate of the reaction and that's because those enzymes are colliding with the substrates more and more frequently at a certain substrate concentration I get this plateau and so at this point the enzyme is working at it maximum rate so again as I increase that substrate concentration I'm going to be finding more and more frequent collisions between the enzyme and the substrate but then at a certain concentration all of the active sites of the enzyme are occupied with substrates so adding more substrates doesn't really make a difference I'm already working or it's already working at its maximum rate one of the experimental techniques that you should be developing in this topic is measuring enzyme catalized reactions okay so we'll take a look at a classic one here you may be even using this um on your own so the reaction between well actually just not between anything hydrogen peroxide in the presence of this enzyme catalase um decomposes into oxygen gas and water okay it would happen naturally anyways this will naturally decompose into oxygen gas and water it's just that this enzyme called cataly definitely speeds up this reaction so let's take a look at some of the things that I can manipulate so for my independent variable I can change a lot of things I might change the temperature I could change the pH I could change the concentration of hydrogen peroxide okay let's just say for example I want to change the concentration of hydrogen peroxide okay so what what I'm going to be doing if I do this is I'm changing the substrate concentration so hydrogen peroxide is my substrate in stores it's generally sold in like a 3% solution I could try 1% I could try 20% I'm manipulating the concentration there of the substrate for my dependent variable I need to count observe or measure something for my results and so there's a few different ways that I could do this um I could try to measure how much hydrogen peroxide is left that seems like it might be difficult or how much water is produced so if we think about this this is a liquid and it's decomposing into a gas and another liquid so I could think about the volume of liquid that's left I could that's kind of hard though I could measure the oxygen gas concentration okay so either with an oxygen sensor or I think what I'm going to pick here is I'm going to pick um the gas pressure so I might use a gas pressure sensor and as this reaction proceeds the faster it goes the faster I should see an increase in gas pressure because this oxygen is a gas and then for my controlled variables these are things that need to stay constant so if we see questions about this on an exam and you've been told that you're manipulating the substrate concentration for sure two things that we should be keeping constant are the other things that we know affect enzymes and we know that that is temperature and pH are there other things that you would want to control if you're doing this lab in your classroom of course these are the two that I would definitely have handy and then um you can think about other ones to add on after that now one of the tricky things here um is the use of this word rate so we've been talking a lot about the rate of these enzyme catalyzed reactions and it's very important that you remember that rate is not only the change but it's the change over time and units are very very important here there are two ways that you can calculate rate if you're designing an enzyme reaction or an enzyme lab you can either choose a fixed amount of time and see what kind of changes happen in that fixed amount of time so I could definitely say I'm going to let this reaction take place for one minute and I'm just going to see what the changes in my gas pressure in that 1 minute that's totally fine you could also fix um the change okay so you could predetermine the level of change that you want to notice and then measure how much time it takes so what I could do is I could say all right I want to see how much time it takes to get a gas pressure increase of 20 kilop pascals that's up to you okay but the units are important so if I'm measuring gas pressure like I just um said in my example that change is going to be in kilop pascals probably there are other units of measure but I would notice the change in a certain amount of time and let's say I was doing this and I was measuring it per minute okay so units are important and if you're designing an experiment it's important that you think about ahead of time which fixed um thing you're choosing either a fixed amount of time or a fixed um uh rate of change or a fixed change and we'll end this video by talking a little bit about how enzymes are actually doing all of this so we know that enzymes speed up reactions and we know it has to do with maybe bonding orientations between our substrates but how are they actually making things go faster well that has to do with this concept of activation energy so whenever you have a chemical reaction even if it gives off energy in the end okay you still have to overcome an energy barrier you have to put energy in before that reaction will proceed and that amount of energy that you have to put in is called activation energy so what enzymes are doing is they're not lowering the energy of the reactants or they're not lowering the energy of the products those things remain the same what does get lowered is the amount of activation energy so with enzyme this activation energy is much lower so you don't need to put as much energy into this system and these reactions should speed up um pretty significantly and so again when we're thinking about theme C interactions and interdependence we really want to think about a couple of things the enzyme and the substrate but also the enzyme and the environment that it's in