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Investigating the Rate of Reaction of the Enzyme Amylase on starch

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Introduction

Individual Investigation: Investigating the Rate of Reaction of the Enzyme Amylase on starch By Osman Khan Lee 13 Aim The aim of my investigation is to see what factors affect the rate of reaction of the enzyme amylase on starch. These factors will be temperature, effect of an inhibitor, the enzyme concentration and the substrate concentration. Starch Starch is a mixture of amylose and amylopectin. Amylose is made up of many monosaccharides units of ?- glucose molecules, joined by alpha 1,4 glycosidic bonds. This builds up a long unbranched chain of glucose molecules, which then coils around itself into a helical structure- rather like a spring. Amylopectin is similar to amylose but also has alpha 1,6 glycosidic bonds, which makes the chains branched. The mixture of these two molecules is starch and is used as energy storage in plants. 1 Left: Diagram showing the structure of amylopectin Right: Diagram showing the structure of amylose The result of the enzyme amylase on starch is the conversion to maltose. This result can be detected by using potassium iodide. If no starch is present the colour of the solution will turn orange. In the presence of starch the potassium iodide turns a dark blue/black colour. As I said earlier the starch molecules curl up into structures like a spring. The hole, which runs down the middle of this spiral, is the same size and shape of the potassium iodide molecule, so the molecules can fit into the spiral. This is what gives the intense blue/black colour when potassium iodide is mixed with a solution of starch. Due to the colour change of the solution, the transmission of light through the solution will vary. Therefore, using a colorimeter, I will be able to detect how the transmission of light through the sample changes. This can then be interpreted on a calibration curve of known starch concentrations, enabling me to find out how much starch is left after a given time period. ...read more.

Middle

I have decided these volumes based on previous research, in which I investigated the action of copper sulphate on catalase. I therefore expect the reaction to occur somewhat the same, with small concentrations having large effects on the output of the enzyme. Once again my standard solutions for this variable will be amylase 3% and starch 1%. As there are 90 readings in total and a cuvette volume of 4cm3, I will require about 360cm3 total solution. I therefore require approximately 180cm3 of amylase and 180cm3 of starch. Amylase 4% 4% of 180 = 7.2 Therefore I must add 7.2g of amylase powder to 180cm3 of distilled water to make a 4% amylase solution As the reactants are being put in as 1cm3 amylase: 1cm3 starch I will require 180cm3 of starch solution. 1% starch 1% of 180 = 1.8 Therefore I must add 1.8g of starch powder to 180cm3 of distilled water to make a 1% starch solution To make the copper sulphate concentrations I will make a total of 10cm3 copper sulphate/water solution. 0.1% Copper Sulphate 0.1% of 10 = 0.01g Therefore I must add 0.01g of copper sulphate to 10cm3 of distilled water to make a 0.1% copper sulphate solution 0.2% Copper Sulphate 0.2% of 10 = 0.02 Therefore I must add 0.02g of copper sulphate to 10cm3 of distilled water to make a 0.2% copper sulphate solution 0.3% Copper Sulphate 0.3% of 10 = 0.03 Therefore I must add 0.03g of copper sulphate to 10cm3 of distilled water to make a 0.3% copper sulphate solution 0.4% Copper Sulphate 0.4% of 10 = 0.04 Therefore I must add 0.04g of copper sulphate to 10cm3 of distilled water to make a 0.4% copper sulphate solution 0.5% Copper Sulphate 0.5% of 10 = 0.05 Therefore I must add 0.05g of copper sulphate to 10cm3 of distilled water to make a 0.5% copper sulphate solution Scientific Theory An enzyme can be defined as a biological catalyst and like any other it is affected by the conditions it is in. ...read more.

Conclusion

The order of reaction is therefore 2. This means that the rate is directly proportional to the concentration of (CH3)3CBr, but the concentration of OH- has no effect on the rate of the reaction. Why is this so? The effect of OH- has been found to not affect the rate of reaction because it occurs in two stages. In the first stage, which is shown in step 1, the C-Br bond breaks heterolyticaly. This therefore means the OH- concentration doesn't affect on the rate of this bond breaking. The second part of the reaction, shown in step 2, is the reaction of the carbocation with the OH-. This stage of the reaction occurs very quickly, like most nucleophilic reactions. Stage 1, however, is slower than this and so the rate depends only on the concentration of (CH3)3CBr. Step 1 is therefore called the rate-determining step. The rate equation for this reaction is therefore Rate = k [(CH3)3CBr] This shows that the rate equation, as stated earlier, cannot be found just by looking at an overall balanced equation. Instead the mechanism of the reaction must be found. In an enzyme-catalysed reaction, the enzyme uses up the substrate. Therefore, to find the order or reaction of that substrate, its concentration must be kept the same. This can be done by just working out the initial rate of the reaction- i.e. when the substrate concentration exceeds the enzyme concentration. Therefore, after doing my practical, I will be able to analyse the results and see what order of reaction the reactants are. 1 Diagram taken from Biology 1 Advanced Sciences page 26 by Mary Jones, Richard Fosbery and Dennis Taylor 2 Diagram taken from Biology 1 Advanced Sciences page 42 by Mary Jones, Richard Fosbery and Dennis Taylor Diagram taken from Salters Advanced Chemistry: Chemical Ideas 10.2 page 225 4 Diagram taken from Biology 1 Advanced Sciences page 48 by Mary Jones, Richard Fosbery and Dennis Taylor 5 Example taken from Salters Advanced Chemistry: Chemical Ideas 10.3 page 235 Osman Khan Lee 13 Page 1 of 22 ...read more.

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