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To Investigate an Enzyme-Controlled Reaction.

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PLAN TO INVESTIGATE AN ENZYME-CONTROLLED REACTION. Prior to planning this experiment an introduction into enzymes and substrates was given. 14/11/02- Week 1 - Discussed enzyme structure and how they work. Properties of enzymes - Activation energy needed for A reaction with or without an enzyme present. Theories of induced fit and lock and key hypothesis. Enzyme/substrate complexes. 21/11/02 - Week 2 - Varying enzyme and substrate concentrations within a Reaction. A BBC computer was used to see how a varying enzyme/ Substrate concentration affects a reaction. A graph was presented on the computer to show rate of reaction The other factors which may affect an enzyme- Controlled reaction were discussed, temperature, pH, Competitive/Non competitive inhibitors. Again, the BBC computer was used to show how these factors influenced a reaction. A class demonstration was performed and observations made of an enzyme-controlled reaction using hydrogen peroxide and potato catalase. After an introduction into enzyme-controlled reactions, I have been asked to investigate one of the factors that may affect the rate of an enzyme-controlled reaction. After taking the above into consideration I have decided to observe if varying potato catalase (enzyme), effects the decomposition of hydrogen peroxide into water and oxygen. To perform this experiment I have decided to vary enzyme concentrations by varying the weight of potato pieces. To observe how varying enzyme concentrations affects the decomposition of hydrogen peroxide, the rate of reaction will be measured by the amount of oxygen released in a fixed time. Consider factors that may affect experiment - temp, pH. 28/11/02 - Week 3 - Practical experiment performed. INVESTIGATION OF THE EFFECT OF ENZYME CONCENTRATION ON A SUBSTRATE The aims of this experiment are to establish if varying the concentration of the enzyme, catalase, affects the rate at which hydrogen peroxide is broken down to form oxygen and water. ...read more.


Where enzymes are absent in a reaction, energy can be given in the form of temperature or pressure that provides molecules with kinetic energy. This overcomes the energy barrier and, enables them to move faster thus more collisions occur. An increase in collisions gives a greater rate of reaction. In the presence of an enzyme the activation energy is lowered and the reaction will occur more readily, even at low temperatures. An increase in temperature above ( 40 to 45 ) can break delicate hydrogen and Ionic bonds which give the enzyme this specific structure. The substrate molecule will no longer be able to bind to the active site as the enzyme is denatured. The experiment was performed at a constant room temperature ( 15 ) and no source of heat was introduced. A possible source of error could have been slight variations in the room temperature, which may have led to some inaccuracies between varying enzyme concentrations. An improvement to this experiment would be to measure the temperature of the reaction with a thermometer. Some reactions transfer energy to the environment (exothermic reaction), which increases the temperature of the reaction. Energy can also be absorbed from the environment (endothermic reaction), in this case temperature decreases. In both these cases, a more accurate measurement would be obtained by using a thermometer. Enzymes are complex globular protein molecules, which have a specific protein tertiary structure. This structure is formed from basic amino acids, which are formed in a particular sequence. This sequence is held together peptide bonds that link each amino acid. The specific structure of the enzyme is given when a polypeptide chain folds back on itself. This folding occurs because there are different areas of negative and positive charge, which attract each other. ...read more.


Within the experiment I varied enzyme concentration, by using different weights of potato pieces. However the exact quantity of catalase present within the potato tissue was unknown. I tried to compensate for this by repeating the experiment twice. An improvement to this would be use 1 molar solution of catalase that could be diluted to form different concentrations, which could measured more accurately. In trial experiments it was found that when I increased potato catalase, they were not all being covered by the 10ml hydrogen peroxide. From this I decided to cut the circular discs into 4 quarters, and found that they all could be covered in the hydrogen peroxide. This also increased the surface area of the potato catalase. I used this to see how changing potato catalase in weight, influenced the breakdown of hydrogen peroxide, as the quantity and speed of oxygen produced is dependant on the rate of reaction. Initially, once the hydrogen peroxide was inserted onto the potato catalase, it was clear that there was a reaction-taking place as bubbles of oxygen gas were transferred via the delivery tube into the measuring cylinder faster within the first minute. Trail experiments proved that after 1 minute it took too long to get a certain amount of oxygen, so I decided to collect oxygen released in 1 minute. The hydrogen peroxide was kept at 10ml throughout each experiment. In trial experiments a greater amount of hydrogen peroxide was used, but this caused a violent reaction as froth travelled into the delivery tube, which prevented oxygen entering the measuring tube, therefore this would have distorted results. In further investigations of enzyme-controlled reactions the experiment could have been repeated more so to obtain more accurate results and the above suggestions and improvements could be taken into consideration. ...read more.

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