Effect of enzyme concentration on initial rate of reaction

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Effect of enzyme concentration on initial rate of reaction

The objective of this experiment is to determine how differentiating the concentration of the enzyme catalase affects the initial rate of reaction, in the decomposition of Hydrogen Peroxide (H2O2)

The equation of this reaction is:

Hydrogen Peroxide(aq)   Water(l)  + Oxygen(g)

2H2O2(aq) + catalase(aq)  2H2O(l) + O2(g)

The source of the enzyme Catalase in this experiment will be yeast, specifically the Saccharomyces Cerewisea strain, as it is easy to obtain and very safe with no harmful effects to the environment.

The technique used to obtain a set of results will be the downward displacement method, where evolved oxygen product from the reaction is passed through a delivery tube and into a water filled burette, pushing the water out of the burette, leaving obtainable results of Oxygen collected. These results will be taken every 5 seconds for two minutes and will give the rate of reaction.

My Equipment will be:

  • Burette
  • Side-arm Conical Flask
  • Bung
  • Tubing
  • Yeast
  • Hydrogen peroxide
  • Water Bath
  • Water/Margarine Tub
  • Distilled water/pH7 buffer
  • Stopwatch

I chose to have a burette to collect the evolved Oxygen, as it has a great degree of accuracy. The gas can be measured to 0.05ml or 0.5cm3.

I chose to have a side arm conical flask to provide a source for the evolved oxygen to travel through easily. Yeast is the chosen source of the enzyme as it is easier to measure than potato slices, as it will be in liquid form and can be measured with a graduated pipette. Also, there will be an even distribution of enzyme and a constant surface area to work in.

Diagram of the setup

Variables/Background Info

Temperature – As temperature rises, the rate of reaction also increases. This happens because the molecules have more kinetic energy (according to Kinetic Theory), so they collide more often, and more of these collisions result in the substrate binding to the enzymes active site. This means that there is more chance of a reaction occurring so the rate of the reaction increases. However if you increase the temperature too much the rate of reaction will decrease. This happens because the active site of the enzyme begins to distort, just like with pH, after a certain temperature, depending on the specific enzyme. The hydrogen bonds, and possibly the disulphide bridges present in the enzyme can break, so the active site changes. This is because when the aforementioned bonds are broken, the structure of the whole enzyme changes, and therefore no enzyme substrate-complexes are able to form. Thus, no product is formed. We say that the enzyme has been denatured, this happens at around 40oC for most enzymes, especially in animals.

     This variable will be investigated further to obtain an optimum temperature that the source of Catalase works at, then this optimum temperature will be kept at a constant.

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Pressure – increasing the pressure can also increase the rate of reaction, this is because the molecules are pushed closer together, and therefore collisions are likely and will occur more often between the molecules, like when you increase the concentration. Hence there is a higher chance of a reaction happening. The pressure in this experiment will be the same at 100kPa (100,000 pascals)

Inhibition – inhibitors either compete against the substrate for the active site of the enzyme, or bind themselves to the enzyme, altering the shape of the enzymes active site, preventing the substrate from binding to the ...

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*** Plan and initial experiments only. This mark is awarded only for the planning section. The inclusion of many different trial experiments means that this experiment has been thoroughly planned experimentally to find the optimum values for the temperature and concentration of Hydrogen Peroxide. The hypothesis is testable and is explained using relevant biological background material. The key variables are considered well. To improve: The inclusion of more relevant background material to inform the plan would be helpful. The material from textbooks or websites should be referenced at the end. The risk assessment is not adequate to be awarded marks under the newest marking schemes and needs to considered much more carefully. The writer needs to ensure that all graphs and table headings are fully labeled with a heading and unit. This should also include sketch graphs used to illustrate a point.