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Investigation in to factors affecting the rate of an enzyme catalysed reaction.

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Introduction

In the human body virtually every metabolic reaction that takes place is catalysed by an enzyme. Enzymes are globular proteins and their molecules are coiled with a precise three-dimensional shape. There are many different groups of enzymes each with their own jobs. An enzyme works by breaking down a substrate into its separate parts. Each group of enzymes works on breaking down different groups of substrates in different parts of the body. Each enzyme and substrate when joined, act like a lock and key mechanism, the enzymes 'unlock' the substrate and out come the products. In order for this to work enzymes have a special site, which the substrate is attracted to. This is the enzymes active site, which is usually a cleft or depression to which the substrate can bind. Enzymes are designed so the substrate can fit perfectly into the active site, and to hold the substrate in place with temporary bonds that form between the substrate and some of the R groups of the enzymes amino acids. There are many factors that affect the rate of enzyme reaction, for example, temperature, enzyme concentration, substrate concentration, pH and inhibitors. Enzymes are suited to the conditions in which they work in, for example protease pepsin; enzymes that work in the stomach are adapted to working in an area with a high pH. The same goes for temperature. Enzymes in the body have an optimum temperature of about 37?C, if they go too far above this temperature or too far below then the enzyme molecule begins to lose its shape and activity and becomes denatured. ...read more.

Middle

After measuring out 15cm3 H202 (5vol) and placing in a test tube you then need to cut up to four or five chunks of liver with a total weight of 1.5 grams, each piece of liver needs to be of approximately the same size to make each test fair. Place the liver chunks in a sealed food bag and weigh down in the water bath, if the liver gets wet then it may effect the results. Place the test tube into the water bath and wait for the solution to reach 22?C (using one of the mercury thermometers). After the H202 has reached the correct temperature, start the stopwatch and leave the H202 and the liver in the water bath for a further five minutes, to give the liver more chance to reach the correct temperature. It will take the liver longer to heat up as it has a greater thickness and surface area than the H202. After five minutes has passed place the liver chunks into the conical flask, then pour in the H202 quickly replacing the rubber stopper as not to let any oxygen escape. It takes a minute to extract the liver chunks from the bag so if you empty them into the conical flask first there is less chance of you losing O2 before the rubber stopper is in place. As soon as the stopper is in position you should then start the stopwatch and time how long it takes for the burette to empty. A burette should be used rather than a measuring cylinder as a burette is much more accurate. ...read more.

Conclusion

and 1.5 grams of liver chunks, for each experiment and for each repeat. One factor that was not controlled was pH; this may have affected the results because if the acidity was not suitable for the enzyme it may have cause the enzyme to denature. The pH factor could have caused the anomaly but also so could a contaminated test tube or piece of liver. An extraneous variable was that each person working on the experiment has different reactions for example one person may have slightly faster reactions when starting the stopwatch. One way to control this is by getting each person to do just one or two of the jobs the same person to start the stopwatch, the same person to weigh the liver, the same person to check the temperature and also the same person to measure out the hydrogen peroxide. Another factor that needs improvement is that the temperature of the liver could not be guaranteed as you cannot test the temperature of a chunk of liver with a thermometer and it may have been better to have used a temperature probe in order to receive more accurate results. On hindsight it may have been better to used a liver solution than chunks, it would have been easier to test the temperature of a solution than a solid, also a liver solution would have had a larger surface area mean there would have been more area for the enzyme active site to come into contact with. Over all though my results did back up my hypothesis even despite the fact that my experimental procedure could have used some more accurate equipment. Cambridge Advanced Sciences: Biology 1 Mary Jones Richard Fosbery Dennis Taylor ...read more.

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