Enzymes only work on one specific type of substrate that means that there is only one kind of substrate will fit into the enzyme's active site. Human’s enzymes optimum working temperature is 37°C (body temperature); however the optimum working temperature of catalase is 30°C. Enzymes have their optimum temperature which is when the molecules of the enzyme are moving at their fastest. This makes it more likely that the enzyme molecules will collide with the substrate and react. At 40°C, catalase becomes denatured, which means the molecular bonds of the enzyme are broken, the active site (the area on the enzyme where the reaction takes place) is deformed and the enzyme becomes useless.
The molecular bonds of enzymes are generally weak and are broken by slight changes in its surroundings, like pH. Our enzymes also have to have the correct pH. Catalase works best at a pH of 7.0. This is because that is the normal pH in most cells. Move away from the optimum pH and the reaction will slow down because if the pH becomes too acidic or too alkaline the catalase will denature and slow down the rate of reaction.
Enzymes must have the correct shape to do their job. Two main theories have been developed on how the enzyme and substrate fit together at an active site.
Emil Fischer put forward the lock and key theory in 1894. It states that it takes the correct key to open a lock. It states that all enzymes active sites are shaped specifically to fit certain substrate. If a molecule of that type is nearby, it will fit into the active site of the enzyme, and will be broken down. However, a different substrate will not fit into the active site of that particular enzyme.
The lock and key theory had some bad points and was not believe to be correct so in 1958, Koshland said that the shape of an active site of an enzyme does not have to be the same type of the substrate. He put forward the Induced Fit Theory. This states that instead of an enzyme having a compliment shape of active site, the active site is able to grab the molecule and fit around it: As the enzyme takes in the substrate, the chemical bonds can weaken in the substrate, helping the reaction to go on. Like the lock and key model, each enzyme catalyzes a reaction only with certain substrates. It is said that both types of reaction occur in the body.
Catalase is an enzyme which makes another hydrogen peroxide undergoes a chemical change without the enzyme chemically changing. Therefore a catalase can be used many times. Without catalysts chemical reactions would take much longer that the average human life expectancy. So that would mean that in 76 years only a couple chemical reactions would take place. Since our bodies have enzymes hundreds of chemical reactions occur in a day. If our bodies didn’t have catalysts our body cells couldn’t function.
All reactions take energy to get them started. This energy is called the activation energy. Enzymes catalyse reactions inside organisms, because they speed up the rate of reaction it is said that enzymes lower the activation energy of the reaction, it lowers the amount of effort needed to get the reaction going.
One molecule of catalase can convert 6 million molecules of hydrogen peroxide to water and oxygen each minute. Catalase can be found in potato cells. When hydrogen peroxide is added to the potato as a liquid, the catalase in the potato breaks down the hydrogen peroxide into water and oxygen two substances which are essential for our bodies. Therefore catalase is essential in our bodies to break down hydrogen peroxide.
Hydrogen peroxide is a by-product of fatty acid oxidation. White blood cells produce hydrogen peroxide to kill bacteria. In both cases catalase prevents the hydrogen peroxide from harming the cell itself. Aerobic (oxygen requiring) bacteria produce hydrogen peroxide as a by-product of metabolism. Hydrogen Peroxide is a toxic chemical, produced by many living organisms as a product of the biochemical reactions occurring in the cells. As hydrogen peroxide is poisonous it must be removed quickly. The enzyme catalase speeds up the reaction that breaks down hydrogen peroxide into water and oxygen.
The Collision Theory
The substrate molecule must collide with the enzyme for a reaction to take place and it must be a successful collision, for this to happen both the substrate and enzyme must have the correct geometry and speed or active site and for it to be able to partake in the reaction.
In order for a reaction to take place, the reacting substances must collide and energy, called the activation energy, must be reached. If the collision between the particles can produce a lot of energy, then a reaction can take place. For the collision to take place, the particles must collide fast enough at the right angle. The higher the number of collisions, the faster the rate of reaction. Increasing the temperature of the substrate can increase the number of collisions.
Inhibitors
Inhibitors slow down the rate of reaction but this sis sometime necessary because it’s a good way of making sure the reaction does not advance too fast.
Reversible inhibitors
Competitive inhibitors are molecules that have a similar structure to the actual substrate and will attach itself temporarily to the active site. The non-competitive inhibitors are molecules but attach with the enzymes but not the active site, but this does not cause the Shape of the enzyme to change, but the reaction rate decreases.
Irreversible inhibitors
The molecules attach themselves permanently with the enzyme, reducing the enzyme concentration and lowering reaction rate.
However, the particles in a solution have to physically come into contact with the catalyst for it to work. Catalase acts on hydrogen peroxide. The more dilute the hydrogen peroxide is, the less common those collisions will be between the hydrogen peroxide molecules, and the catalase molecule. As a result, the reaction will take place more slowly. The amount of oxygen and water given off is directly proportional to the amount of hydrogen peroxide that has been reacted, as the catalyst breaks down hydrogen peroxide, the water and oxygen is given off as a breakdown product of hydrogen peroxide, as the reaction continues, there are fewer and fewer molecules of hydrogen peroxide remaining in the solution as time goes on, and so less collisions between hydrogen peroxide and the enzyme. The more water and oxygen produced, the less hydrogen peroxide is left to react. The concentration of hydrogen peroxide in the solution then decreases, and the reaction slows down. The reaction slows down, because the concentration of hydrogen peroxide in the solution is lower.
Hydrogen Peroxide---------------------->Water + Oxygen
2H2O2 ------------------------> 2H2O + O2.
If the temperature is too low the enzyme molecules will not have enough energy to collide with the hydrogen peroxide molecules, so the reaction will not carry on. As the temperature gets hotter, the rate of reaction will then increase as the molecules have more energy. One way to measure the rate of a reaction, is to measure the amount of product being produced. In this case, the products are water and oxygen, but in this case oxygen will be measured and time would be in seconds.
The substrate and the catalase are always on the move so there is a big chance that they will collide forming the enzyme substrate complex; this is catalase-hydrogen peroxide complex. When the hydrogen peroxide fits into the catalase’s active site, enzyme + product which are enzyme-oxygen & water complex is made this are Enzyme-product complex which is catalase + water & oxygen.