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Investigate the effect of pH on the rate of enzyme-controlled reactions.

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Introduction

PLAN: Investigate the effect of pH on the rate of enzyme-controlled reactions Aim: The specific enzyme that will be examined and utilized within this investigation is 'catalase' (present within a quantity of potato extract). In order to determine the enzyme's optimum pH a series of experiments must be carried out where the pH concentrations (buffer solutions) are changed, while the substrate (hydrogen peroxide) and enzyme concentrations remain constant. Hypothesis, Prediction and Scientific Background: Catalase: an enzyme, found in peroxisomes, which catalyses the decomposition of hydrogen peroxide, which results from oxidation reactions in the cell; to yield water and oxygen. High concentrations of catalase are found in the liver. Furthermore catalase is the fastest known enzyme and an important part of the body's antioxidant defences. Therefore catalase is a protein that, in small amounts, speeds up the rate of a biological reaction without itself being used up in the reaction (i.e. it acts as a catalyst). The enzyme acts by binding with the substance involved in the reaction (the substrate - hydrogen peroxide) and converting it into another substance (the product of the reaction - water and oxygen). As the enzyme is relatively specific in the type of reaction it catalyses; hence there are many different enzymes for the various biochemical reactions. The enzyme requires certain pH conditions for optimum activity; where a maximum and efficient amount of products are formed. Therefore catalase is an enzyme that brings about (catalyses) the reaction by which hydrogen peroxide is decomposed to water and oxygen. It is found extensively in mammalian tissues, catalase prevents the accumulation of and protects the body tissues from damage by peroxide, which is continuously produced by numerous metabolic reactions. pH: a scale, which measures the concentration of hydrogen ions in a solution. Solutions with pH values below seven contain high concentrations of hydrogen ions and are acidic. Solutions with values above seven have low concentrations of hydrogen ions and are alkaline. ...read more.

Middle

or substrate concentration (hydrogen peroxide) remain controlled, and therefore will not be able to cause serious problems when analyzing results and forming a final conclusion. As a result of this the only factor, which is altered while all others remain constant is the pH of the buffer solution to ensure reliability of results. Thus the variables of temperature, enzyme and substrate concentration (volume of solutions) must be kept at a constant while the experimental factor; the pH buffer solution is the only single factor that is changed. Another factor that must remain a constant is the temperature, which may be difficult as fluctuations occur due to excess heat produced by the body and by light, as well as the continual motion of air. Furthermore the same potato extract solution must be used for the entire investigation, as another solution will inevitably contain different quantities of enzymes. Therefore due to this difference in catalase concentrations it will cause variations in results measuring the rate of reaction (product formation) when compared to the results from the initial potato extract solution. To keep the temperature constant the beakers containing the solutions could be stored within a water bath. Therefore in order to minimize or restrict temperature change, each experiment must be performed in an isolated area where the factor remains a constant. By carrying out these precautions a clear and precise conclusion can be drawn, so that an analysis of results and the essential problem - investigating the effect of "pH" do not contain limitations or errors. When the extract has been inverted, a small rubber tube connected to a long glass tube will be directly fitted over the mouth of the syringe. The apparatus will then be positioned on a piece of paper, to which a mark will be sketched to represent the starting position of the liquid in the tube, when this has been achieved a stopwatch will immediately be started. ...read more.

Conclusion

Experiment 1 2.0 2.0 2.0 Experiment 2 2.0 2.0 2.0 Experiment 3 2.0 2.0 2.0 10 Experiment 1 2.0 2.0 2.0 Experiment 2 2.0 2.0 2.0 Experiment 3 2.0 2.0 2.0 Analysis: A line graph will be drawn to highlight the rate of reaction - how far the liquid in the glass tube travels from its initial point to its new position after one minute (mm. min-1) when different pH concentrations are used. Therefore by producing a line graph results can be analysed appropriately and observed to determine any anomalous readings. Due to this the errors may be removed or isolated so they do not cause significant affect on the final conclusion. From the graph the optimum pH can be established (the peak of the curve) as well as the effects different pH's have on the activity of catalase's enzyme-controlled reactions. I believe the graph may bare similarity to the one show below: A graph will be constructed according to the mean values (mm. min-1), which will provide theoretical values, whereas the results from the experiment provide the practical values. Thus as the rate of reaction values are mean values the curve will be a line of best fit. In addition it may be necessary to construct another line to portray the median values, if the medium values are too extreme or unreliable to form an adequate analysis. A generally applicable schematic diagram of the variation in the mean (average value of three results) rate of an enzyme catalysed reaction (y-axis) with the pH of the solution (x-axis). The centre of this inverse parabola displays the optimum pH of the enzyme catalase; where a maximum amount of substrate molecules (H2O2) are broken down to yield the products water and oxygen. The oxygen is consequently measured to indicate the rate of enzyme-controlled reactions. Extremely high or low pH values generally result in complete loss of activity for a majority of enzymes, as it affects the stability of enzymes. Christopher Magee Wednesday 15th January 2003 1 ...read more.

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