The Decomposition of H2O2 using Catalase, in yeast as a catalyst.

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 Chemistry/Biology joint investigation

The Decomposition of H2O2 using Catalase, in yeast as a catalyst.

Prediction

Hydrogen Peroxide decomposes to water and oxygen. When yeast is added, the enzyme Catalase in the yeast speeds up the decomposition. The formula for the decomposition of H2O2 with Catalase is:

                            Catalase

H2O2        H2O + ½ O2

        Reactions in living cells, for example, liver cells, produce H2O2, which is poisonous. Catalase renders it harmless by breaking it down into oxygen and water. This is a catabolic reaction, meaning that the H202 molecule is split into two smaller molecules, H20 and ½ O2. This can be explained using the lock and key theory. All enzymes are specific, which means we can think of Catalase as a lock, which is shaped so that H2O2 is the only key that will fit and the only molecule it will break down.

        

 

The Catalase speeds up the decomposition of H2O2 because it is a catalyst; this means it can take part in a reaction without undergoing a permanent change. A Catalase molecule can break down H2O2 into ½ O2 and H2O many, many times without undergoing a permanent change. Catalase speeds up the reaction because it lowers the activation energy required for the H2O2 to decompose. It provides an alternative route of lower activation energy.  The energy needed to start the decomposition is lower because the Catalase weakens the chemical bonds by forming weak interactions with the H2O2 molecules.

I am going to investigate the effect of temperature on the rate of decomposition of H2O2. I predict that as the temperature increases, the rate of reaction will increase. Mackeans says, “An increase of temperature of 10°C will double the rate of reaction.” So I predict that if at 20°C I saw 15cm3 of oxygen given off in 15 seconds, then at 30°C I would see 30cm3 given off in the same time period.

The rate of decomposition increases because the kinetic energy of the Catalase and H2O2 molecules increases as the temperature rises. The molecules are moving about more, meaning they collide more frequently. This increases the chance of collision between the H2O2 and the active site of the Catalase molecule; therefore the rate of decomposition should increase. A graph showing rate of reaction against temperature might look like this.

                                                

        Catalase is an enzyme, therefore it will have an optimum temperature and it will be denatured at a certain temperature. The H2O2 will decompose fastest at the optimum temperature; this is when there will be the maximum number of successful collisions between the H2O2 and the active site of the Catalase. At this temperature, all the available Catalase and H2O2 molecules will collide. Catalase is an enzyme found in human cells, and the optimum temperature for enzymes found in human cells is 37°C, or body temperature. I predict that the optimum temperature for the Catalase will be between 30°C and 40°C.

         The rate of reaction should keep on increasing between O°C and the optimum temperature; I have already said that for most reactions there is a doubling of rate for every 10°C increase. After the optimum temperature, the Catalase will denature. This happens because Catalase, being an enzyme is a protein. Heat changes the shape and structure of the protein in such a way that the H2O2 molecules can no longer bind with the active site of the Catalase.

        So, I predict that the rate of decomposition of H2O2 and therefore rate of reaction will increase as the temperature rises, until the optimum temperature is reached. After this temperature is reached, the rate will decrease until it stops altogether due to the Catalase being denatured.

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Pre-tests

        In order to find the most effective method I decided to carry out some pre-tests. These helped me to discover the most accurate and safest way to carry out this experiment. The volumes and temperatures I tested helped me to find out the best procedure to take.

Pre-test 1

  • 0.1g yeast used
  • 5cm3 H2O2 used
  • This experiment was carried out at room temperature.
  • A gas syringe was used to measure the volume of O2 given off.

        There was a large amount of O2 given off in the first 30 ...

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