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Investigating the effect of substrate concentration on the rate of an enzyme controlled reaction.

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Introduction

Investigating the effect of substrate concentration on the rate of an enzyme controlled reaction Aim: to find the effect substrate concentration has on the rate of reaction of an enzyme controlled reaction. I have decided to measure the rate of reaction of the break down of hydrogen peroxide when using catalase. I have decided to use this reaction for the following reasons: from preliminary work I found that this reaction occurs at a speed suitable for measuring with the equipment available at school. This experiment is also suitable as I am familiar with it from doing similar experiments in GCSE biology. Introduction Enzymes have the ability to catalyse an experiment, for this reason they are often used to speed up reactions which don't go fast enough naturally. It speeds up a reaction by lowering the activation energy(Ea) thus meaning more collisions between reactants result in successful reactions taking place: This diagram shows that by adding a catalase we lower the activation energy consequently increasing the number of particles able to react successfully. What the diagram doesn't demonstrate is the fact that the reaction finishes faster but the same amounts of products are produced. The substance that the enzyme acts on is called the substrate. In the reaction I am using in my experiment the substrate of the catalase is hydrogen peroxide. The function of the enzyme can be explained by the lock and key theory: Picture from: www.ghs.gresham.k12.or.us/science/ps/ Diagram 1 on pg 1 shows the lock and key theory of how enzymes work, we must also consider the induced fit model though as this may be how catalase enzyme works: Both theories are similar in that at stage 2 the enzyme and substrate join to form an enzyme substrate complex, but are different because the substrate and active site of the enzyme are complimentary in the lock and key theory whereas in the induced fit theory the active site is a similar shape to the enzyme and it changes slightly to allow the enzyme substrate complex to form. ...read more.

Middle

rate of reaction of the breakdown of hydrogen peroxide; if the molecules get heated up then they will possess more kinetic energy, meaning an increase in collisions per second resulting in an increase in rate of reaction, we will therefore attempt to do the whole experiment on the same day in the space of 1 hour in which there will only be minor changes in temperature. Another reason for temperature to be kept constant is the fact that if the temperature got too high usually around 37�C the enzyme would be denatured, that is, the hydrogen bonds holding the tertiary structure together would be broken and the shape of the active sites would change meaning that it wouldn't work correctly. Volume of enzyme and substrate: An increase in either enzyme or substrate would lead to an increase in reaction rate we therefore need to make sure that we measure everything as accurately as possible. Concentration of yeast: If the concentration of the yeast was increased then it would mean that there would be more catalase for the hydrogen peroxide to bind with as there would be an increase in the number of active sites available. We will therefore use yeast from the same sample and attempt to do the experiments all on the same day. pH level: Enzymes are denatured at certain pH levels and work at different speeds depending on the level: The effect of pH on rate of reaction We will have to use the same batches of yeast and of the different concentrations for each experiment. Washing of equipment: When washing for example test tubes it is essential that they are dried thoroughly because any water left in them would dilute the solutions. Syringes: we must make sure that when syringes are used, they are used for the same substance each time because if we mixed them up, it would contaminate either the yeast or the hydrogen peroxide. ...read more.

Conclusion

Highest volumes of water were used for lowest concentrations this would mean that it appears that they have a lower rate of reaction than they should compared with the higher concentrations when less water was in the solution meaning less gas was being dissolved. When the bung is put into the test tube when setting up the experiment and when the hydrogen peroxide is inserted into the test tube via a hypodermic needle, air will have been displaced this would make the readings higher than they should be, but because the same amount of air was displaced for each experiment it would not affect the shape of the graph. This is demonstrated by the fact that the experiment for 0% H2O2 produced 3ml of gas when if there is no substrate for the enzyme to act on, no products can be formed. It can therefore be said that the 3ml of gas in the gas syringe was due to air displacement. In order to rectify this 3ml could be subtracted from the results of each experiment but as it makes no difference to the shape of the graph and therefore the conclusion there is no point. One last confounding variable that was beyond my control was the temperature of the room. If the room heated up at any time in the experiment it would have speeded up the rate of reaction due to the molecules possessing more energy, this would result in more movement meaning more collisions per second resulting in successful reactions. If there were a decrease in temperature, the opposite would happen. If there were any temperature changes throughout the experiment it would make the results unreliable, as the solutions would have had different levels of energy. E.g. If there was a temperature increase at the beginning (a) and then a decrease back to normal in the middle(b) of the experiment, then a further decrease in temperature at the end(c), the graph that would be produced is shown alongside what it would be like it temperature remained constant Biology Coursework Anna Moore 1 ...read more.

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