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An Investigation into the effect of substrate concentration on the activity of the enzyme catalase.

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Introduction

An Investigation into the effect of substrate concentration on the activity of the enzyme catalase. Introduction This experiment is designed to examine how the concentration of the substrate (Hydrogen Peroxide) affects the rate of reaction of the enzyme catalase. Catalase is a particular protein. All enzymes are globular proteins. Enzymes are essential for maintenance of life, because without them reactions occurring in living organisms would be so slow that they would hardly be worth occurring at all. It would be possible to increase the speed of reactions by simply increasing the temperature, but for the temperature to have a significant effect on the rate of reaction the temperature would have to be raised to a level that would kill the organisms by disrupting their membranes, as well as being expensive energetically. This is one of the main advantages of enzymes; they enable metabolic reactions to proceed rapidly while maintaining low temperatures. Activation Energy In many reactions, the substrate will not be converted to a product unless it is temporarily given some extra energy. This energy is called activation energy. Enzymes decrease the activation energy of the reaction, which they catalyse. They achieve this by holding the substrate in such a way that their molecules can react more easily. Reactions that involve enzymes take place much faster at lower temperatures than they would without them. The diagram below shows the enzymes lowering the activation energy. Active Site A few of the amino acids on the surface of the molecule fold inwards to make a specific indentation, called the active site, into which a particular substrate can fit. Once the enzyme and the substrate are joined they form an enzyme-substrate complex. The formation of an enzyme-substrate complex makes it possible for substrate molecules to be brought together to form a product. The product is released and the enzyme is free again to take part in another reaction. Enzymes are unchanged during this process, and so they are able to break more substrate molecules into products. ...read more.

Middle

6. The gas syringe has to be held in place by a clamp. The positioning of this is also important for it must be level otherwise gravity will have an effect on the results. 7. The conical flask and gas syringes need to be connected by a delivery tube; using fairy liquid here may be useful as it can be a bit tight. You need to check the set-up is airtight by gently pulling the gas syringe, if it is brought back to it's original place it means it's airtight, if not the apparatus needs to be double checked. 8. Put a needle onto the end of the syringe, and push this into the suba seal, as quickly as possible you need to squirt the liquid into the conical flask. Once this has been done record the level of the gas syringe, and do so every minute until ten minutes is up. 9. Wash and tidy up all the equipment you used. Safety Hydrogen peroxide will be used throughout this experiment, so goggles must be worn constantly to avoid any damage because hydrogen peroxide is a corrosive chemical. In addition to this gloves must also be worn to protect skin, as minor spillages are common. It is essential to wear a laboratory coat to prevent any chemicals damaging clothing and reaching the skin underneath. In both of the methods a scalpel is used to cut the celery, and if these aren't used sensibly they could cut the skin. Most dangerous however is the needle in method two as the syringe contains hydrogen peroxide. Because of this fact the needle should only be put on the syringe just before it's needed and taken off immediately afterwards. Method Two Preliminary Results Amount of oxygen evolved (cm) Minutes Hydrogen Peroxide 80% ( cm ) Hydrogen Peroxide 20% ( cm ) 0 9 10 1 12 11 2 14 11 3 15 11 4 16 11 5 16 11 6 16 11 7 16 11 8 16 11 ...read more.

Conclusion

As I was using an inverted burette I think I can be quite confident of the accuracy of my measurements, for burettes are very precise and have clearly marked values along the side. Apart from reasons already discussed, the most significant limitation of the method I used is the lack of an airtight environment. Using a gas syringe connected to a suba seal is the obvious solution to this problem, but as I experienced problems with this during my preliminary experiments I thought it wasn't practical to use, but many others from my class were able to produce reliable results from it, so given the chance where I could be assured the results were reliable I would use a gas syringe. Improvement on accuracy of results could be achieved by minor changes such as increasing the number of repeats used, so that the average was worked out using more sets of results and overall improving it's reliability. As oxygen was still being produced at a steady rate when I terminated the experiment after 10 minutes, it could prove useful to continue recording the results for a further 10 minute as this might mean more trends could be identified between the different concentrations levels and the analysis could be covered in more depth. I have focused mainly upon the discrepancy between the 80% and 100% concentration levels but there are also other points for discussion. If you look at the table displaying the results recorded for the 60% solution of hydrogen peroxide solution you'll see that the first repeat produced reasonably more oxygen than the second two repeats, I think this can be explained using reasons I outlined earlier, the first repeat was carried out on a different day to the other two so the hydrogen peroxide and celery would have been different and this lead to a discrepancy. I believe that the first result is probably most accurate. This also explains why the lines on the graph for the 60% and 40% are so close as the 60% should probably have been higher. ...read more.

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