[Music] in this video we are going to continue to build our knowledge of proteins by discussing enzymes if you want to refer back to General Knowledge about proteins you can look back at section b1.2 enzymes are globular proteins that perform specific roles within cells they work to assist chemical bonds of other molecules to either put them together or break them apart and they make this process easier which we will talk about in detail later in this video what we need to understand about enzymes is that their structure is everything they only work because they have a specific structure called an active site that is designed to bind with only one other specific substance this active site contains a subsection called a catalytic site that is only a few amino acids in length but the interactions between the overall three-dimensional structure of the enzyme which includes the bonding site ensure that the active site overall has the necessary properties in order for the buildup or breakdown of material to be supported another small point to know is that enzyme names generally end in ASE so if you see these terms lactose versus lactase you can easily identify that lactase is the enzyme and actually functions to break down the disaccharide lactose let's dive into more detail about the structure of enzymes and how they function there are many different chemical reactions taking place in the body that are supported by enzymes and because one enzyme can only bond with one type of molecule your body creates a lot of different enzymes to allow all of these reactions of different molecules to take place we call this unique oneandone pairing of enzymes and their active site to one substrate which is the one molecule it combined with enzyme substrate specificity if a different substance happens to collide with the active site that does not fit no bonding will occur and therefore no reaction will happen it's like a love story where every active site only has one or a few which we will discuss later specific substrates for them and it's just a matter of finding them in the sea of all the other molecules within the cell when they do find each other and the substrate does fit into and bind with the active site the process of induced fit bonding occurs which means that both the substrate and active site change shape this alteration in shape makes it easier for B BS within the substrate molecule to break and new bonds to form when the process is complete and the product of the reaction detaches from the active site the shape of the active site reverts back to its original structure which allows another of the same substrate to bond to it later on so the process can happen over and over again we said earlier that enzymes work to build and break down macro molecules they have the unique ability to support and increase the rate of these reactions without actually changing the nature of the reaction action which is really amazing they literally speed up the chemical reactions that take place in our body and for this reason we classify enzymes as catalysts which again are molecules that can impact the rate of a chemical reaction and speed it up enzymes are not used up or altered in the process as we saw on the last slide which means that they can continue to be reused for the same chemical reaction over and over again enzymes are extremely important for the human body because without them many of the reactions that need to take place would happen much slower which is time that our cells do not have based on how we have evolved so enzymes can speed up chemical reactions but how does that actually work how can something speed up a chemical reaction when you take a look at a chemical reaction you need to understand that energy is required to reach what is called a transition state that substances need to get to in order for a reaction to occur the energy level needed to be reached for the reaction to happen is called the activation energy this is basically the energy required to get the molecules in the correct position and to overcome the forces of repulsion so that the bonds can be arranged along with the actual breaking or forming of the bond itself if we take a look at the red line in this graph which just shows the relative change in energy we can see that the activation energy required for water and carbon dioxide to naturally come together in the correct way to alter their bonds and form carbonic acid H2 CO3 is all the way up here again this is naturally without the assistance of an enzyme but if we take a look at the Blue Line you can see that if this chemical reaction is supported by an enzyme the amount of activation energy greatly decreases this is because the enzyme is working to bring the two substances together in the correct orientation and Alters their shape slightly so it is easier for the bonds between them to form this means that less overall activation energy is required for this reaction to happen with an enzyme making the reaction easier to complete under normal circumstances meaning it will occur more frequently which is what we mean when we we say it is a catalyst that is speeding it up energy is required to break bonds within a substrate which means that energy is needed as input for the break to occur this leaves the product at a higher energy State than they started as we can see in this graph here there is an energy yield when bonds are made to form the products of an enzyme catalyze reaction this releases energy which leaves the products in a lower energy State than when it started as seen here based on the changes in energy in the system we call this reaction endo thermic and this reaction exothermic make sure to know how to read these activation energy graphs for the IB exam when discussing enzymes you have to also talk about the process of metabolism within the human body Metabolism is defined as the summation of all chemical reactions that take place in the body that use energy to build up and break down molecular structures and a very very large amount of the reactions that take place in the body are supported by enzymes this is important because as we discussed on the last slide enzymes make reactions Easier by lowering the activation energy required for substrates to become products in addition to reducing activation energy enzymes play an important role in metabolism because of their enzyme substrate specificity because only certain enzymes can assist certain reactions the body can control to an extent when these reactions occur this can happen in a few ways one of which is as simple as creating an enzyme at a certain time if the cell does not need a certain reaction to speed up it simply will not transcribe and translate the instructions for that enzyme to be made and if there is no enzyme then obviously it can't function on the other hand if the cell does need to speed up a particular reaction it can create more of those specific enzymes that will ensure the reaction takes place we'll talk about this role of metabolism in more detail over the next few slides within the process of metabolism there are two different Pathways that are used to build molecules up and break them down we have already mentioned them in the video but now let's put a vocabulary term to each one as you will see it on the IB exam the process of building molecules up which means connecting monomers together via chemical bonds to form polymers is called anabolism and the point of bringing this topic up in this video is because the vast majority of these reactions are supported by enzymes which speed up their rates of reaction there are many examples of this talked about throughout the IB Biology curriculum and manifests in many examples of condensation reactions we have talked about like the formation of a peptide bond between amino acids covered in section b1.2 the formation of a longchain polysaccharide like a glycogen in section b1.1 and the process of photosynthesis which is covered in C 1.3 all of these processes are classified as anabolic because they are polymers built up by connecting pieces monomers together with chemical bonds again supported by enzymes and I am sure as you can guess if anabolism means building up catabolism means breaking down this can be seen with hydrolysis reactions that work in opposition to condensation reactions which break chemical bonds apart turning a polymer back into many monomers we see this happen in the process of digesting food which needs to be broken down to be able to be absorbed by the body which has many many enzymes that play a part in that process and the oxidation of components in cellular respiration to yield energy we will talk about both of these large ideas more specifically in other videos but right now just know that catabolism plays a role in both of those processes in order for these metabolic reactions to take place like anabolism and catabolism both substrates and enzymes need to come together but remember that molecules this small are not alive and do not have any agend genda or even have the ability to have an agenda like higher order thinking animals like humans do these molecules can't think for themselves and they do not in any way try to come together the process is really random in a sense that these enzymes and substrates need to get very close to each other in order to bond to the active site this means that movement is required by either the enzyme the substrate or both the enzyme and the substrate in order for them to bump into each other the cytoplasm of cells is a solution of compon compon dissolved in water so in order for these pieces to come together they need to randomly move through the water and if they get close enough to bond and interact they do and the enzyme can work to support the reaction it was designed for now we have established that most enzymes are made out of proteins and because that is the case there can be some external factors that affect protein structure which subsequently means they can affect enzymes as well we know that the active site is the bonding location for the substrate and this is dependent upon the shape of the active site to fit properly to help catalyze the reaction but if the structure of the protein or the enzyme in this case gets changed it can affect its ability to function altering the active site in any way means the substrate will not be able to bind properly rendering the enzyme useless this process is referred to as denaturation and the enzyme in this case we can say is denatured we also touched on this concept in the b1.2 video about proteins the two main ways this can happen is by change in temperature or pH to the external environment in either case if temperature increases enough or pH changes enough the tertiary structure of the protein can be altered causing changes within the enzyme as a whole with the substrate not able to bind the reaction cannot be catalized because of this altered denatured shape enzymes work to catalyze reactions and the speed at which they do this can be measured as enzyme activity but this enzyme activity or the rate at which all of the enzymes that support a specific reaction can work can be affected by a few things let's say we have this example of five of the same substrates and 10 of the same enzymes all of which can catalyze the reaction of this particular substrate and right now the total rate of enzyme activity is let's say about half of an arbitrary maximum value so things are working well but they could be more efficient if the temperature of the system were to change let's say that it increases the molecules within the system will start to move faster this will increase increase the speed of the substrates and the enzymes and allow more of an opportunity for them to interact and bump into each other ultimately increasing the enzyme activity but this will only increase to an extent because we know that if temperature gets too hot the enzyme can start to denature rendering them useless resulting in a decrease in enzyme activity additionally we can assume that if the temperature decreases the molecules will have less kinetic energy and move slower causing a decrease in enzyme activity next we have changes in PH what we need to know here is that enzymes are designed to work effectively within a specific PH range so if you have enzymes designed to work in the stomach which is a very acidic place they will be highly effective in a low PH other places in the body would have enzymes more effective at a neutral pH now the idea here is that a shift from the optimal pH for any enzyme can change its solubility and overall shape effectively denaturing it not being able to bond to the active site means enzyme activity will decrease and this goes both ways for an increase and decrease in PH from the optimal peak of enzyme activity lastly we have substrate concentration in this example so far we have been operating with five substrates over 5 Seconds of time with 10 total enzymes if we were to increase the amount of substrates we would have 10 and we could effectively double the rate of enzyme activity because we would be utilizing all of the enzymes at any given given moment so increasing the substrate concentration can greatly increase the overall rate of enzyme activity but only to a maximum point if we were to add five more substrates per 5 Seconds to this example for a total of 15 substrates we can see that the substrates now outnumber the available enzymes so it would still only catalyze 10 over the 5 Seconds because we only have 10 enzymes to do the job with every enzyme being used the rate of activity will stagnate because of the limiting factor so the graph is best drawn like this make sure you know the difference between all three of these graphs and be able to draw them and talk about them for the IB exam we looked at enzyme activity reaction rate graphs on the last slide being able to calculate reaction rates is a skill you need to know for the IB exam and could also help you with your IIA if you choose to complete an experiment that deals with enzyme activity when experimenting with reaction rate scientists are usually measuring how quick enzymes work to two catalyze reactions you can measure the speed of this reaction in two ways in the first method you can start with a known amount of substrate and record the time it takes for all of the substrate to become converted into products or the second method is to set the enzymatic reaction to occur for a set period of time and measure the amount of product formed in that time frame or the amount of substrate that is used during that time in either case the quantity of your measurement can be divided by time to get you a rate of reaction which is also then telling you the speed at which the reaction is taking place this example is testing the effect of temperature on cataly activity in a solution of hydrogen peroxide cataly breaks down hydrogen peroxide creating oxygen and water and when this happens in this experimental setup the oxygen will move through the delivery tube and be collected in the cylinder if we set this up for a period of time and had a few different experimental trials at different temperatures we can measure how much oxygen is produced over time which informs us of the speed of the reaction taking place under those different temperature conditions it is likely that your teacher will have you complete an enzyme wet lab within your classroom that deals with these skills make sure to always have your independent dependent and controlled variable set with purpose and intent to answer your scientific question [Music]