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The Effect Of Copper Sulphate On Pepsin Activity.

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THE EFFECT OF COPPER SULPHATE ON PEPSIN ACTIVITY Introduction My coursework is investigating the way copper sulphate affects pepsin activity. Pepsin is an enzyme. Enzymes are globular proteins, which have a specific 3D structure, which is determined by its tertiary or quaternary structure. In spite of their size only a small area is functional, the active site, which binds with the substrate as shown below in Fig.1. Enzymes act as biological catalysts which mean they are used to speed up reactions which otherwise would take longer to complete. They work by lowering the activation energy, the minimum amount of energy, required by the substrate, casein, for it to hydrolyse. Key A. The amount of activation energy required without the use of an enzyme. B. The amount of activation energy required with the use of an enzyme As you can see from Fig.2 the amount of activation energy which is to be overcome for a successful reaction is considerably lower with the help of an enzyme. The way in which an enzyme works is similar to that of a lock and key. The substrate temporally attaches itself to the active site to create an enzyme substrate complex. Once together the enzyme hydrolyses the substrate and breaks it up. It then releases the products. If we relate this to the lock and key theory it is evident that the enzyme's active site, 'the lock', is specific to the substrate, 'the key'. However this is not entirely true as the enzyme can change shape slightly to fit other similar fitting substrates; this is known as the 'induced to fit theory'. Pepsin is one of three proteolytic, protein digesting, enzymes in the digestive system; the other two are trypsin and chymotrypsin. Pepsin is found in the gastric glands of the stomach. It is secreted into the stomach in the form of gastric juices along with hydrochloric acid, rennin and mucus. ...read more.


Volume of stock solution (cm3) Volume of distilled water (cm3) 0.25 5 5 0.1 2 8 0.05 1 9 0.025 0.5 9.5 0.01 0.2 9.8 0.005 0.1 9.9 Once the six different concentrations of copper sulphate had been made up I put 10cm3 of the first concentration of copper sulphate, 0.25%, into a boiling tube using the graduated pipette and pipette filler. Then, as with the copper sulphate I put 10cm3 of casein, 2%, into another boiling tube using the graduate pipette and pipettes filler. I also put 10cm3 of trypsin, 0.5%, into another boiling tube using the graduated pipette and pipette filler. This meant that I had three separate boiling tubes, one with 10cm3 of copper sulphate, my inhibitor, one with 10cm3 of casein, my substrate and one with 10cm3 of trypsin, my enzyme. I placed all three boiling tubes into a testube rack whilst I set up the electronic water bath, to 37oC. After I had set up my water bath I placed the testube rack along with the three solutions into the water bath. In order to maintain accuracy when considering temperature I placed one thermometer into each of the different solutions, the copper sulphate, casein and trypsin. When all three solutions were at 37oC, I poured the trypsin solution into the copper sulphate solution. I then allowed the two solutions to incubate together in the electronic water bath for 2 minutes, which I timed using the stopwatch. After the incubation period I immediately mixed the casein solution with the copper sulphate and trypsin solution and placed the copper sulphate, trypsin and casein solution back into the water bath. Whist doing so, I reset the stopwatch and began timing again as well as taking the first absorbency reading. To take an absorbency reading I used the colorimeter along with the cuvettes. I would extract a sample of 3cm3 of the solution from the boiling tube using the graduated pipette and pipette filler. I would then put this sample in a cuvette. ...read more.


With each case I cannot determine accurately the rate of stirring. This is could cause inconsistencies within my result as if I stir one solution more then I had others it would gain more kinetic energy, which as a result would cause more successful collisions between enzyme and substrate molecules therefore speeding up the rate of reaction. To overcome this I could use a mechanical stirrer that stirs each test solution at a steady rate. When obtaining my results I took 3cm3 sample of the main solution to test for absorbency readings. This obviously will not produce an accurate representation of the whole experiment, as parts may not be mixed evenly, causing imprecise results. Additionally, due to removal and replacement of samples from the main solution some of the solution is lost which causes a decrease in volume as well as concentration. This could cause a change in the rate of reaction, as fewer particles would collide creating less successful collisions. Both limitations could be overcome by the experiment being done on a smaller scale so that samples are not necessary. When carrying out my experiments I was only allowed to incubate my enzyme and inhibitor together for 2 minutes due to time restrictions. If I had sufficient amount of time to carry out all my investigation I would consider incubating the trypsin and copper sulphate for longer to make sure the all of the possible enzymes were inhibited before adding the casein. Further Work In order to provide further evidence for my conclusion, I would carry out further work to my investigation. I would firstly carry out more tests with a variety of different sources of trypsin, casein and copper sulphate, as the one source of trypsin may act differently to another. I would also use a larger range of copper sulphate concentrations to fully investigate in more detail how an inhibitor such as copper sulphate affects trypsin activity. In addition I would use a buffer solution to control the pH when carrying out experiments as this may add to accuracy to my results. ...read more.

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