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An investigation to determine how the rate of an enzyme-catalysed reaction is affected by the availability of the active site of the enzyme during the reaction by using the enzyme catalase to decompose hydrogen peroxide.

Extracts from this document...

Introduction

Rishi Patel Planning for AS coursework on " An investigation to determine how the rate of an enzyme-catalysed reaction is affected by the availability of the active site of the enzyme during the reaction by using the enzyme catalase to decompose hydrogen peroxide" Aim The aim of this investigation is to determine how the rate of an enzyme-catalysed reaction is affected by the availability of the active site of the enzyme during the reaction. The effect on the rate of the reaction by the availability of the active sites on the enzyme catalase to decompose hydrogen peroxide will be studied. Safety precautions It is important to wear safety spectacles and plastic gloves at all times when carefully handling the hydrogen peroxide as it is extremely irritant to the skin and eyes. It is necessary to be careful when cutting tissues with the blade, which should be put away in its case when not in use. It is also necessary to follow the standard laboratory rules and take care not to touch the water bath once it has been heated up. Scientific knowledge A catalyst is a substance, which speeds up a chemical reaction but remains unchanged at the end of the reaction. All metabolic reactions in living cells are catalysed by enzymes. These are biological catalysts made of globular proteins, coiled into precise 3D shapes with the hydrophilic R groups on the outside of the molecule; therefore enzymes are soluble in aqueous solutions. The chemical/ chemicals, which an enzyme acts on, is called its "substrate". The area where the substrate binds to the enzyme is called the "active site" of the enzyme. This is usually a cleft or depression and has a specific shape. This allows the substrate to fit perfectly and the combined structure is called the "enzyme-substrate complex". The shape of the active site allows only one shape of molecule to fit exactly and hence the enzyme is said to be "specific" for this substrate. ...read more.

Middle

40mls of 20vol hydrogen peroxide was added via the measuring funnel and the volume of oxygen released into the gas jar measured at 15seconds, 30secs and at 45secs, from when the hydrogen peroxide was added to the potato chip. Another 2cm wide potato chip sample was taken from the same potato using the same cork borer but this time the chip was cut in half so that two 1.0cm wide pieces with the same diameters were obtained. The above procedure was repeated but both the pieces were added to the conical flask. Another 2cm wide potato chip sample was similarly cut into three pieces, each 0.66cm wide. The above procedure was repeated, but with the three pieces added to the conical flask. The results were noted as shown in the table below. A table to show the volumes of oxygen obtained at various times when 40mls of 20vol hydrogen peroxide was added to different samples of potato chips Sample No. Conical flask contains : Volume of Oxygen measured in the gas jar/ mls At 15 sec At 30 sec At 45 sec 1 1 potato piece 2 cm wide 30 34 37 2 2 potato pieces each 1 cm wide 34 37 39 3 3 potato pieces each 0.66 cm wide 39 41 43 It can be seen from the results above that when the 2cm wide chip is cut into further pieces, the volume of oxygen measured at each time period increased. This suggests that as the surface area increases, the reaction occurs faster as expected, suggesting that more active sites on the enzyme are available, as the surface area increases. For the actual investigation, some improvements will be made to the procedure: The conical flask, measuring funnel, the 50ml measure used to measure the hydrogen peroxide, the rubber bung, the blade and tile used for cutting the potato will all be rinsed out with distilled water to ensure that the pH remains neutral and is not affected by any traces of chemicals left over from previous use of the equipment. ...read more.

Conclusion

From the results, graphs will be plotted of the average volume of oxygen collected/mls on the y-axis and time/second from when the hydrogen peroxide is added on the x-axis. for each sample number. The following table will be used to note all results: Sample No. Conical flask contains. Volume of Oxygen measured in the gas jar/ mls At 15 sec At 30 sec At 45 sec At 60 sec 1 1 potato piece 3 cm wide 1 potato piece 3cm wide 1 potato piece 3cm wide Average 2 2 potato pieces each 1.5cm wide 2 potato pieces each 1.5cm wide 2 potato pieces each 1.5cm wide Average 3 3 potato pieces each 1.0 cm wide 3 potato pieces each 1.0 cm wide 3 potato pieces each 1.0 cm wide Average 4 4 potato pieces each 0.75cm wide 4 potato pieces each 0.75cm wide 4 potato pieces each 0.75cm wide Average 5 5 potato pieces each 0.6cm wide 5 potato pieces each 0.6cm wide 5 potato pieces each 0.6cm wide Average Control No potato added Secondary Sources BIOLOGY 1: M.Jones et al Cambridge university press 2001 BIOCHEMISTRY: R.Fosbery Cambridge university press 2002 BIOLOGICAL SCIENCE 1: D.J.Taylor et al Cambridge university press 2001 PRE-EVALUATION From the experiment there will be some inaccuracies: The 50ml measuring cylinder used to measure the hydrogen peroxide will have a percentage error of 0.5ml X 100 = 1.25% 40ml Vernier Callipers- used to measure the potato pieces will have a percentage error of 0.1mm X 100 = 0.33% if a 3cm width measurement is done 30mm 0.1mm X 100 = 0.66% if a 1.5cm measurement is done 15mm Therefore the smaller the measurement the greater the percentage error. Gas jar - used to measure the volume of oxygen collected will have a percentage error of 0.5ml X 100 = ? Volume of oxygen collected in mls The smaller the volume of oxygen collected the greater the percentage error. Thermometer - used to double check that the temperature in the water bath remains at 35 C. This will have a percentage error of 0.5 x 100 = 1.43% 35 ...read more.

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