Investigation on the effect of the concentration of hydrogen peroxide on the rate of reaction of the enzyme catalase
Plan
Aim
- My aim is to investigate the amount of oxygen produced by the effect of the concentration of hydrogen peroxide on the enzyme catalase.
Scientific explanations
- Enzymes are biological catalysts that speed up a chemical reaction, but remain unchanged at the end of the reaction. Enzymes are large globular protein molecules with a specific shape. They are therefore specific in the reactions that they catalyse - one enzyme will react with molecules of one substrate.
- Enzyme molecules have a special feature; an active site. This is the area on the surface of the protein where another molecule or molecules can bind. This molecule is the substrate of the enzyme. The shape of the active site allows a perfect fit held by temporary bonds formed between the substrate and R groups of the enzyme’s amino acids. The enzyme binds to the active site forming an enzyme- substrate complex, and the reaction takes place immediately. Certain enzymes break a substrate down into two or more products (catabolic reaction) other enzymes bond two or more substrates together to assemble one product (anabolic reaction). This is known as the lock and key theory.
- The induced fit theory is when the active site isn’t the correct shape in which the substrate can fit, however, as the substrate approaches the active site, the site changes and this results in it being a perfect fit, after the reaction has taken place, the active site returns to its normal shape.
- Enzymes reduce activation energy. Every reaction requires the input of energy. Enzymes lower the level of activation energy needed as shown by the graph taken from Letts AS BIOLOGY,
- The higher the activation energy the slower the rate of reaction. An enzyme lowers the amount of energy required for a biochemical reaction to take place. The available energy when an enzyme binds with a substrate has a greater effect, and the rate of catalysis increase. In this investigation we will be considering the factor of concentration on the effect of the rate of progress. When the concentration of enzymes is low, the substrates are less frequently occupying the active sites, and the rate of reaction is low. As the enzyme concentration increases, there are more active sites and the reaction can take place at a faster rate. Eventually, when the substrate molecule becomes a limiting factor, the enzyme concentration has no effect.
- This graph taken from OCR Biology 1 shows that the initial rate of reaction increases linearly against enzyme concentration.
- The graph shows that the more enzymes present, the more active sites will be available for the substrate to fit. Under the condition that there are enough substrates available, the initial rate increases linearly with enzyme concentration.
- This graph shows the results of an investigation in different amount of catalase added to the same amount of hydrogen peroxide, however in our investigation we will be investigating the different concentrations of hydrogen peroxide to the same amount of catalase, so we should consider the affect of substrate concentration.
- As the substrate concentration increases the initial rate also increases, as the substrate binds to the active site more often. However if the substrate concentration increases and the enzyme concentration is constant the active site of each enzyme is working continuously. The enzymes can’t work faster if more substrates are added but they have to ‘queue up’ for an active site to be free and the enzymes are working at their maximum rate (Vmax).
- This graph taken from the OCR Biology 1 shows the curves of oxygen released against time. The effect of substrate concentration of an enzyme- catalysed reaction.
- This shows that as the substrate concentration increases, the initial rate of reaction also increases. However if we go on increasing substrate concentration, keeping the enzyme concentration constant, it reaches a point where the enzyme simply can’t work any faster, and is working at its maximum possible rate; Vmax.
- Catalase is an enzyme present in the cells of plants, animals and aerobic (oxygen requiring) bacteria. Catalase catalyses the decomposition of hydrogen peroxide, a powerful and potentially harmful oxidizing agent, to water and molecular oxygen.
- H2O2 H2O + O2
- In this reaction H2O2 is the substrate and H2O + O2 are the products.
- When a slice of potato is placed into a solution of hydrogen peroxide, bubbles of oxygen form on the potato surface and rises to the top of the solution. Potatoes contain catalase, an enzyme that breaks down hydrogen peroxide into water and oxygen.
- Under favorable conditions, the reaction occurs very fast. The maximum catalytic rate for one catalase molecule is 6 million molecules of hydrogen peroxide broken down to water and oxygen each minute. The reaction product is 6 million molecules of water and 3 million molecules of oxygen. (Because the oxygen molecule consists of two oxygen atoms, the number of oxygen Molecules made in the reaction are half the number of water molecules.)
- Other factors that we aren’t directly changing, should be take into consideration as they can also affect the rate of reaction, are temperature and PH.
- Increasing the temperature increases the rate of reaction as heat energy reaching the enzyme and substrate molecules causes them to increase random movement as the substrate binds to the active site more often as it gains kinetic energy. When the substrate collides with more energy, bonds are more easily broken.
- As with temperature, enzymes have an optimum pH. If the pH changes much from the optimum; neutral or slightly alkaline conditions, the chemical nature of the amino acids can change.
This may result in a change in the bonds and so the tertiary structure may break down. The active site will be disrupted and the enzyme will be denatured.
