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Investigating the effect of enzyme concentration on the rate of an enzyme catalysed reaction.

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Investigating the effect of enzyme concentration on the rate of an enzyme catalysed reaction. Aims: This is an experiment to investigate how the concentration of the substrate Hydrogen Peroxide (H2O2) affects the rate of reaction of the enzyme Catalase, in yeast cells. catalase product The formula: 2H2O2 2H2O + O2 Background information: Enzymes such as catalase are globular protein molecules found in all living cells. They are biological catalysts, and are used to speed up a specific reaction rate within the cell. They reduce the level of activation energy needed in a reaction, which speeds up the rate of a reaction. The higher the activation energy, the slower the reaction will be. The two graphs below show the amounts of activation energy needed with and without an enzyme: All enzymes contain an active site, a depression in the enzyme molecule, where a specific substrate molecule can fit into exactly and bind to. All enzymes have a substrate molecule, which is the same shape as its active site. When the substrate binds to the enzyme's active site, it forms an enzyme-substrate complex, which produces the product(s). Enzymes only perform one type of reaction, and only have one specific type of substrate to do this. Catalase is an enzyme found in food such as potato and liver, and is used to remove Hydrogen Peroxide from cells, as it is the poisonous by-product of metabolism. There are two types of enzyme-substrate metabolic reactions: anabolic and catabolic. An anabolic reaction is when there is a two-part substrate which is built together to form a new molecule. A catabolic reaction is where one substrate is broken down to produce two products. The two diagrams show both of these reactions which show the lock and key theory: An anabolic reaction: A catabolic reaction: There are four factors that can affect the rate of an enzyme reaction. They are: o The pH o The temperature o The concentration of the enzyme solution o The concentration of the substrate solution. ...read more.


This could result in loosing some oxygen whilst we put the bung back in the conical flask. Therefore, from the range of methods I have seen I have decided to use a side-arm conical flask connected to a gas syringe. To add the yeast, my original idea was to use a syringe, although it would not hold 40ml of yeast. Therefore I will put the yeast in the conical flask with a buffer and then add the hydrogen peroxide using a syringe through the bung. I have also realized that I have not controlled the temperature. Therefore I will keep the conical flask in a water bath set at 30?C throughout the experiment. A final diagram of the apparatus I am going to use is shown below: Apparatus: ?Stand ?Clamp ?Boss ?Bung cut into two ?Conical flask with side arm ?10cm3Hydrogen peroxide (two molar) ?40cm3 of Yeast ?Buffer ?Automatic pipette ?Gas syringe ?Beakers ?Goggles for eye safety ?Laboratory coat to protect skin and clothes ?Stop clock ?Syringe ?Water bath set at 30?C. I have chosen the stand, clamp and boss to hold the gas cylinder, horizontally in the air to be sure that it is not affected by any variables. The conical flask and the bung is used to hold the enzyme solution and the substrate, also to stop any gas from escaping, as we are measuring the oxygen gas. The bung will be cut in half to allow the syringe holding the hydrogen peroxide to penetrate. The conical flask has a side arm that allows the gas to be transported to the gas syringe via the delivery tube. The rubber delivery tube is used to transport the gas to the gas syringe to be measured and to minimise the amount of oxygen lost. The buffer will control the pH of the yeast. The water bath will control the temperature. I will use an automatic pipette, as it is very accurate and precise as it measures every m1000th mil. ...read more.


If this happened then when would I stop the clock? Should I stop timing when it is flat on the surface or if it is on its side at the top? The other problems were with the technique. The size of each filter paper square were not exactly the same. Some were slightly different sizes, and some were slightly thicker than others. This could be a problem because if the paper was too big then more of the enzyme could be absorbed. Therefore more oxygen could be produced and there could be a faster rate of reaction. This would also be inaccurate. Another problem was that I didn't time how long I left the filter paper in the yeast solution. This could also have meant that more of the enzyme could be absorbs, so more oxygen may be produced causing a faster reaction rate. To overcome this problem I could time how long the paper was left in the yeast solution. However, this would cause further problems with accuracy, as everyone's reaction times are different. Overall I feel that the biggest problem was the accuracy when timing. The paper would sometimes turn onto its side and fall, before it reached the surface. Also it was hard to decide whether to use the results when this happened. To improve this problem you would need to use something more accurate than a stop clock. Something that stops timing once it reaches a certain point. You would also need to stop the filter paper from turning onto its side and falling. You could something to keep the paper stable. If we used a different shape then it could not turn onto its side. Maybe a sphere or a cube instead of a square of filter paper. If I were to do this experiment again I would take into account all the problems I have noticed here. I will also try to be more accurate. However despite these criticisms I do feel that my conclusion is reliable, as I only had two anomalous results, and it does support my prediction. ...read more.

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