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Experiment to Investigate a Factor which Affects the Rate of Decomposition of Hydrogen Peroxide by Catalase.

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Introduction

Phil Cooper L6 10.11.01. Experiment to Investigate a Factor which Affects the Rate of Decomposition of Hydrogen Peroxide by Catalase Aim The aim of this investigation is to investigate a factor which affects the rate of decomposition of hydrogen peroxide using the enzyme catalase. Background Catalase is present in nearly all the peroxisomes of nearly all aerobic cells, serving to protect the cell from the toxic effects of hydrogen peroxide by catalysing its decomposition into molecular oxygen and water. The overall reaction for this is: 2 H2O2 2 H20 + O2 The enzyme is among the most efficient known, with rates up 200,000 catalytic events/second. 'Hydrogen peroxide, H2O2, is a colourless, syrupy liquid that is a strong oxidising agent and, in water solution, a weak acid. It is miscible with cold water and is soluble in alcohol and ether. Although pure hydrogen peroxide is fairly stable, it decomposes into water and oxygen when heated above about 80�C; it also decomposes in the presence of numerous catalysts, e.g., most metals, acids, or oxidisable organic materials. A small amount of stabiliser, usually acetanilide, is often added to it. Hydrogen peroxide has many uses. It is available for household use as a 3% (by weight) water solution; it is used as a mild bleaching agent and medicinally as an antiseptic. The 3% solution is sometimes called ten volume strength, since one volume of it releases ten volumes of oxygen when it decomposes.' (www.encylopedia.com) Variables In this experiment, there are a number of variables which may affect the rate of reaction. These are: * temperature at which the reaction takes place * pH at which the reaction takes place * concentration of the enzyme * concentration of the substrate * enzyme inhibition * Temperature - as the temperature at which the reaction takes place is increased, the rate of reaction will increase up to a point. From this point the rate of reaction will decrease to a point at which it will be zero. ...read more.

Middle

The activity of almost every enzyme is a cell is regulated by feedback inhibition. Feedback inhibition is an example of common biological control mechanism called negative feedback. Just as high temperature will cause furnace to shut off, in a similar manner the product of an enzyme can inhibit a enzyme reaction. When the product is in abundance, it binds competitively with its enzyme's active site; as the product is used up, inhibition is reduced and more product can be produced. In this way the concentration of the product is always controlled within a certain range. Activation of an allosteric enzyme by an activator is another form of feedback inhibition. Combination of the activator and the allosteric site cause a conformational change in the active site permitting substrate binding and the reaction will be caltalyzed. (ntri.tamuk.edu/cell/enzyme2.html) Prediction I predict that as the concentration of catalase increases, so too will the rate of reaction, up to the maximum possible value where a plateau will appear on the graph. The rate of reaction will increase in proportion to the concentration of the enzyme catlase. Hypothesis To explain the prediction, first the action of an enzyme needs to be explained. The first and most simple explanation is the 'lock and key' hypothesis. An enzyme is a globular protein, coiled into a precise 3D shape. This has an active site, which is a depression into which another molecule can bind. This molecule is the substrate of an enzyme, as it has a complementary shape which fits into the shape of the active site perfectly. Each type of enzyme will usually only act on one type of substrate molecule, as the shape of the active site will usually only allow one shape of molecule to fit in. For this reason the enzyme in said to be specific for this substrate. The enzyme then catalyses a reaction into which the substrate molecule is split into two or more molecules, called the products. ...read more.

Conclusion

An open ended syringe was used as opposed to an upturned measuring cylinder because if there was a gas bubble at the top it could easily be removed by opening the top of the syringe, meaning more accurate and reliable results could be used because the water always filled the whole syringe. * 10% yeast solution - this solution provided enough catlase for the reaction to produce quite a lot of gas so the final pattern was more easy to discern. This made it easier to make conclusions as the results were spread apart more so it was easier to spot a pattern in the results. * 5cm3 syringe - a number of these were used. They were used to measure out the volumes of water and yeast to be mixed. This volume was used because it was the closest to the volumes needed, but small enough to mix accurate quantities of the water and yeast. A clean syringe was used each time to ensue accuracy. * 20 vol. hydrogen peroxide - there was a choice between 5 vol. and 20 vol. It was decided that the reaction would occur more quickly with 20vol hydrogen peroxide so this was used because it allowed for more readings to be taken in the time available, meaning that conclusions could be drawn more reliably as there were more results. * Clamp stand and boss - this set-up was needed for support of the test tube, and this set-up is reliable and easy to adjust. * Test tube and bung - the yeast solution needed to be contained in something, but gas needed to be able to escape from the top. The bung had a hole in which was connected to the delivery tube, so the gas could travel quickly from the test tube into the syringe. * Gas delivery tube - the gas needed to be transferred from the test tube to the syringe, and the only way to do this was by gas delivery tube. ...read more.

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