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To investigate the effect of substrate concentration on the activity of an enzyme.

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Biology Investigation: Enzymology- Catalase Aim: To investigate the effect of substrate concentration on the activity of an enzyme. Background Information: ( The image above shows a 3D structure of catalase from E.coli. The structure was solved using Xray Crystallography. Enzymes are biological catalysts which speed up biochemical reactions, they lower the activation energy. Enzymes are globular proteins which catalyse metabolic reactions. In an enzyme- catalysed reactions, the substrate binds to the active site of the enzyme. The enzyme and the substrate are held together in an enzyme-substrate complex by hydrophobic bonds, hydrogen bonds and ionic bonds. The enzyme then converts the substrate to the reaction products which are released leaving the enzyme to form another enzyme-substrate complex. The enzyme is recycled again and again. One enzyme molecule can carry out 1000 of reaction cycles every minute. Eventually the enzyme will breakdown. Each enzyme is unique for a certain reaction because its amino acid sequence is arranged in a certain way. The active site has a specific shape so that only one or a few of the thousands of compounds present in the cell can interact with it. Any substance that blocks or changes the shape of the active site will interfere with the activity and efficiency of the The diagram below shows the breakdown and the building up of a reaction: There are several factors that will effect the enzyme's activity: Salt Concentration: If the salt concentration is very low, the charged amino acid side chains of the enzyme will stick together. The enzyme will denature and form an inactive precipitate. If the salt concentration is very high, normal interaction of charged groups will be blocked and the enzyme will precipitate. An intermediate salt concentration such as blood (0.9%) or cytoplasm are optimum for most enzymes. pH: Enzymes amino acids contains group such as -COOH and NH2 that gain or lose H+ ions. ...read more.


Temperature (C?) H2O2cm3 H2Ocm3 5 0 4 1 3 2 2 3 1 4 Obtaining: I carried out my experiment accordingly to my plan and check that I am following my safety and fair test regulations. I discovered that there were some things that I will have to change to ensure that my experiment was as fair as possible. * I used a variety of differently sized measuring cylinders rather than having one big cylinder (which was very difficult to measure out small concentration), a small was later required to measure out the small concentrations. * I also used different cylinders for the different reactants, I used one cylinder to measure out the volume of distilled water and another cylinder for measuring out the hydrogen peroxide. Observations: I am measuring the time in which 10cm3 of oxygen is produced when a piece of liver is placed in differently concentrated hydrogen peroxide and water solution. The time in which 10cm3 of oxygen is produced will be timed by a stop watch, the oxygen will be measured by using a gas syringe. Results: I followed my method and carried out the experiment three times to justify my first two sets. After obtaining the results, I displayed my results into tables. Below is the table of results, which displays the time taken for 10 cm3 of oxygen to be produced. Concentration of hydrogen Time taken for 10 cm3 of O2 to be collected (s) Temperature (C?) H2O2cm3 H2Ocm3 5 0 37.90 36.02 39.07 18 4 1 42.97 43.79 45.21 18 3 2 75.78 70.40 73.94 18 2 3 197.08 200.33 196.56 18 1 4 319.83 327.64 331.07 18 From looking at my results, I need to display it onto graph, but to be as accurate as possible I will need to find an average from the times. I selected two times that were closest to each other and worked an average from them. ...read more.


I will research and perform experiments around these areas: How the activity of the enzymes and rates of reaction are affected by: * Temperature * Surface area * Physical state of the reactants * Applying pressure To back up my prediction, conclusion and obtained results, I will conduct other experiments that are about the activity of an enzymes. I will do an experiment on how temperature affects the activity of an enzyme. The theory is that as you increase the temperature, rates of reaction will increase. If I increased the temperature by 10?C then rates of reaction doubles. The reason why is because the activation energy Ea is increased as particles moves faster. To see if this theory is true I will do the same experiment. But this time I will keep: * The volume and the concentration of hydrogen peroxide constant. * The surface area, mass of the liver the same (using the same quantity of Catalase) This is because I will not be experimenting the affects of rated of reaction as concentration varies; I will be looking at temperature. These are the factors I will change: * I will change the temperature- varying it depending the selected range. * I will be using a water bath to help me vary the temperature. * I will be using ice, warm and hot water. Although this experiment seems safe, there are risks if the experiment is not carried out probably. For example I don't want to boil the acid as it could be perilous. So my safety precautions will still apply. I also have to consider the fair test regulations and so forth. Here is a diagram of my apparatus for this experiment: Here are the range of temperature I will be using: * 0?C * 10?C * 20?C * 30?C * 40?C Readings will be taken every three minutes into the experiment. The results will be analysed by using graphs to compare and justified whether it backs up my prediction. To back up my results I will repeat the experiment again. 1 ...read more.

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