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Enzyme Concentration

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Introduction

The effect of substrate concentration on the rate of reaction Aim I have been set with the task to find out whether substrate concentration affects the rate of a reaction. The enzyme I will be using is catalase, which is found in liver. Hypothesis My hypothesis is that a greater concentration of particles will cause more reactions to occur. There will be a positive correlation between the initial rate of reaction and the substrate concentration, however there will come a point where the rate of reaction will reach its maximum level Vmax, meaning that all the enzymes' active sites have been filled and no more oxygen can be produced. "The rate of an enzyme-catalysed reaction increases in direct proportion to the substrate concentration until the reaction reaches a maximum rate. After the maximum all the active sites of the enzyme molecules are filled, so increasing the substrate concentration further as no effect on the rate of reaction."1 My hypothesis of having a greater rate of reaction due to substrate concentration, therefore only applies when there is an excess of enzymes. Prediction I predict that the more concentrated the substrate is, the initial rate of oxygen produced will be higher. I have come to this prediction as; the substrate concentration increases, the rate of reaction increases because more substrate molecules can collide with the enzyme molecules, so more reactions will take place. However, the effect of substrate concentration is subject to the limiting factor of enzyme concentration, and above a certain concentration the rate of reaction will stop increasing. The rate of reaction is quickest at the beginning when there is a high concentration of substrate. Later, the volume of substrate decreases so the reaction slows down. Eventually all the substrate is used up so the reaction stops. ...read more.

Middle

I decided then to use 4mls of hydrogen peroxide, and yet again the experiment had finished within a matter of seconds. Finally, I found the right amount of hydrogen peroxide to use; which was 3mls. And finally by doing the preliminary work I found the best way in which to carry out the experiment. I initially started by making all the different concentrations on after the other. E.g. when doing the experiment for 0.2M, I only made enough 0.2M solution for one experiment when still had 2 more experiments to do. I realised this was extremely time consuming. So for my experiment I decided to make 20mls of each concentration and keep it in a beaker, so I had enough solution for all three experiments. Risk Assessment RISK EFFECT PROTECTION ACTION TO TAKE IF SPLIT ON SKIN, EYES, SURFACES, OR SWALLOWED Hydrogen Peroxide Hydrogen peroxide is a corrosive and an irritant; at high concentrations it is very dangerous. However, during this experiment I am only using a very dilute solution. To avoid contact with skin and eyes, eye protection such as goggles should be worn, also for skin; gloves should be worn at all time whilst dealing with the chemical. If the hydrogen peroxide manages to get onto hands; wash with warm water and soap immediately. If got into contact with eyes or swallowed seek medical assistance. Wash off surfaces immediately. Liver homogenate If swallowed, uncooked liver can cause illness; such as diarrhoea. In order to avoid contact with liver homogenate; wear gloves at all times. If the liver homogenate manages to get onto your hands was immediately with warm water and soap. If swallowed seek medial assistance. ...read more.

Conclusion

This provides the link between the substrate concentration and rate of reaction being a linear relationship. Increasing the substrate concentration increases the probability of collisions between enzyme and substrate molecule, so causing the catalysation of the substrate to proceed faster. I also predicted that that the effect of substrate concentration is subject to the limiting factor of enzyme concentration, and above a certain concentration the rate of reaction will stop increasing. When the rate of reaction reaches its maximum possible rate, Vmax, all the enzymes' active sites have been filled and no more oxygen can be produced. "The rate of an enzyme-catalysed reaction increases in direct proportion to the substrate concentration until the reaction reaches a maximum rate, Vmax. After the maximum is reached, all the active sites of the enzyme molecules are filled, so increasing the substrate concentration further as no effect on the rate of reaction."4 In order to see Vmax on graph B, I will have to go up to a much higher substrate concentration. This will allow me to see where the graph tails off. (Refer back to figure 1, on page 2) However, as there is a clear linear relationship on graph B, this shows the experiment was carried out with an excess of enzymes present, i.e. the limiting factor of enzyme concentration did not affect the results of this investigation. I know this as the graph does not level off (as shown in 'factors affecting enzyme activity'). I also found that the rate of reaction is quickest at the beginning when there is a high concentration of substrate. Later, the volume of substrate decreased and so the reaction slowed down 1 Kent, M; Advanced Biology 2 Wikipedia.co.uk 3 www.myelin.org/glossary.htm 4 Kent, M; Advanced biology ?? ?? ?? ?? Puja Patel ...read more.

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