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Determine the extent to which a pH affects enzyme effectiveness.

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The aim of this investigation is to determine the extent to which a pH affects enzyme effectiveness. This was measured via absorbency techniques, using the colorimeter. Apparatus Water Bath set to 40�C Colorimeter Cuvettes Test tubes 10ml measuring cylinders Glass pipette Small and large beaker Tweezers Test tube rack Thermometer Live enzyme (pepsin 2%) Denatured enzyme Buffers, 2, 3, 4, 5, 6, 7, 8 Stop watch Marker pen Strips of 35mm x 5mm photographic film Sticky Labels Safety * Wear lab coat * Wash your hands thoroughly before and after the experiment. * Never eat or drink in the lab * Report any accidents, breakages or spillages * Wear goggles throughout the experiment and take precaution when handling the acidic buffers. Method * Two sets of test tubes were labelled 2, 3, 4, 5, 6, 7, 8 respectively1. * All the test tubes were placed in the rack, ready for solutions to be added to them. * Using a 10ml measuring cylinder 3ml of pepsin and 3ml of pH 2 buffer were accurately measured using separate cylinders2. * This was repeated for the rest of the pH buffers 3, 4, 5, 6, 7, 8. ...read more.


This shows that the solution contains the most precipitate, and thus, the optimum pH must be 3. The absorbency levels drop rapidly either side of this value, however, much more significantly closer to pH neutral and basic conditions. Evidently, the effect is more significant the more the pH deviates from pepsins optimum pH 3. This indicates that it has altered the ionic bonds, which help to determine the tertiary structure of the protein. This has lead to distorted protein recognition. As a result, pepsin was unable to break down the gelatine, which binds the silver halide salts to the photographic film. The graph indicates that the enzyme has become completely inactive, or denatured, by the time the pH is 8 as there is a absorbency of 0 on average. Spearman's rank correlation is used to determine if an association exists and also the strength of the association. If one set of measurements increases as the other decreases, they are negatively correlated. A perfect negative correlation has a value of -1. This value can then be compared with the critical value of r according to the number of pairs of measurements. If r is greater or equal to the critical value then the null hypothesis can be rejected, and it can be evaluated that a significant correlation exists. ...read more.


The heat gives the enzymes added kinetic energy and so increases their movement and therefore, their activity. 6 Tweezers are used to prevent contamination by the hands. 7 The photographic film was added in 20 second intervals so that they may be removed in 20 second intervals, thus spending an equal amount of time in the soulutions. This makes the results more reliable as it is a fair experiment. 8 A stopwatch is used as this is an accurate measurement of time 9 The films are left for this amount of time so the enzymes have opportunity to degrade the substrate and a better difference of effectivity becomes more obvious in the resukts. 10 This ensures that the photographic film is left inside the solutions for an equal amount of time. Making the test fair and results more reliable. 11 The solutions were shaken to suspend the black silver bromide crystals. This ensures that they do not sit at the bottom of the test tube. 12 When putting anything in colorimeter assure that the lid is firmly closed so no excess light can enter and effect results ?? ?? ?? ?? Ashleigh MacDonald Investigating the Effect of pH on the Activity of an Enzyme ...read more.

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