The effect of temperature on catalase activity

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                                                                                                                           Jessica Leung

The effect of temperature on catalase activity

Hypothesis

I predict that the breakdown of Hydrogen Peroxide will be quicker when the temperature is increased until it exceeds 40°C, the enzymes optimum temperature is at 35°C. This is because a rise in temperature increases the rate of most chemical reactions and a fall in temperature will slow them down. In many cases a rise in 10°C will double the rate of reaction in a cell. This is particle theory. I am going to investigate the temperature at which reactions occur. I predict an increase in temperature will result in an increase in kinetic energy. Since the speed of particles increases, they should collide more often and therefore the speed of reaction increases. The particles will also have more energy thereby speeding up the reaction even more. It has been suggested that for every 10 degree rise in temperature, the speed of the reaction will double.

At low temperatures particles of reacting substances do not have much energy. However, when the substances are heated, the particles take in energy. This causes them to move faster and collide more often. The collisions have more energy, so more of them are successful. Therefore the rate of reaction increases.

The more successful the collisions are the faster the reaction.

The same can be said for reactions controlled by enzymes, but because enzymes are proteins if the temperature exceeds 50°C the enzyme will be denatured and will no longer work. For this reason few cells can tolerate temperatures higher than approximately 45°C.

Enzymes are specific in the reactions they catalyse, much more so than inorganic Catalysts. Normally, a given enzyme will Catalyse only one reaction, or type of reaction. The enzyme has an active site that helps it to recognise its substrate in a very specific way. Just like a key only fits into a specific lock, each enzyme has its own specific lock; each enzyme has its own specific substrate. This is called the lock and key theory. The enzymes never actually get consumed in the process; they just increase the rate of reactions.

When enzymes denature the heat starts to destroy their shape and structure. The shape of the enzyme is so important to its working that any change in the shape of the molecules will make them less effective or stop them working completely. Therefore I predict that by heating the Hydrogen Peroxide, when it reacts with the enzyme the shape of the enzyme will be ruined due to the high temperature.

So the higher the temperature of the Hydrogen Peroxide and Catalase solution, the less effective the reaction will be.

Variables 

 In this investigation, the variables that affect the activity of the enzyme, Catalase, were considered and controlled so that they would not disrupt the success of the experiment.

i) Temperature - As temperature increases, molecules move faster (kinetic theory). In an enzyme catalysed reaction, such as the decomposition of hydrogen peroxide, this increases the rate at which the enzyme and substrate molecules meet and therefore the rate at which the products are formed. As the temperature continues to rise, however, the hydrogen and ionic bonds, which hold the enzyme molecules in shape, are broken. If the molecular structure is disrupted, the enzyme ceases to function as the active site no longer accommodates the substrate. The enzyme is denatured.
To control this variable, the temperature was maintained at a fairly constant level that allowed the enzyme to work effectively (room temperature, approximately 23ºC). This was achieved by using a test tube rack and tongs to handle the apparatus so that the heat from my hands did not affect the Catalyse.

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ii) pH - Any change in pH affects the ionic and hydrogen bonding in an enzyme and so alters it shape. Each enzyme has an optimum pH at which its active site best fits the substrate. Variation either side of pH results in denaturation of the enzyme and a slower rate of reaction.
In this experiment, the pH should be kept constant using a pH 7 buffer, selected to maintain a pH level suited to the enzyme by being equal to the natural environment of the enzyme (potato tissue).

iii) Substrate Concentration - When there is an excess of enzyme ...

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*** A good account of the investigation but the use of more A level standard biological language would have improved its quality. There is a lot of repetition of relevant theory in places and in the analysis section theory is not related to actual results effectively.