An active site is a region on the surface of an enzyme to which substrates bind and which catalyzes a chemical reaction involving the substrates. Thus the inhibitors prevent the enzyme activity when the concentration of the substrates is very low. As the substrate concentration increases so does the enzyme activity. Non-competitive inhibition is an Enzyme inhibition in which the inhibiting compound does not compete with the natural substrate for the active site on the enzyme but inhibits reaction by combining with the enzyme-substrate complex after the complex is formed.
An example of a non-competitive inhibitor is ATP. When ATP accumulates it binds to a site other than the active site on the enzyme phosphofructokinase. In doing so it changes the enzyme conformation and lowers the rate of reaction so that less ATP is produced. Hypothesis: There is an inverse relationship between the mass of lead nitrate and the ability of amylase to convert starch into maltose. Variables: Independent Variable: ?The mass of lead nitrate dissolved in each of the solutions. Dependent Variable: ?The change in the color intensity of the iodine. Controlled variable: Time: the reaction was allowed to proceed for twenty minutes. ?Temperature: the water bath was set at 40? C. This was to provide the optimum conditions for the enzyme activity. ?Volumes of the respective solutions: The volume of the starch solution (10 cm3), the volume of the amylase (10 cm3) and the volume of water (5 cm3). The exact volumes were measured out with the help of a syringe. Materials: 1. Syringe 2. 6 test tubes 3. Stop watch 4. Water bath 5. White spotted tile 6. 5% amylase solution 7. Iodine solution 8. Lead nitrate crystals. 9. 6 boiling tubes. 10. A pipette. Procedure: 1.
The water bath was fixed at 40? C. 2. The six boiling tubes were labelled A-F and then each was filled 10cm3 of starch solution with the help of a syringe. 3. Different quantities of lead nitrate were then added to the 6 test tubes labelled 1-6. The quantities were: 0. 00gm; 0. 10gm; 0. 20gm; 0. 30gm; 0. 40gm and 0. 50gm. 4. In the test tube 10gms of 5% amylase was then added. 5. The contents of each test tube were then transferred to the boiling tubes i. e. the contents of test tube 1 were transferred to boiling tube A and so on. 6. The boiling tubes were then placed in a water bath with a fixed temperature at 40?
C. 7. The reaction was allowed for 20 minutes. 8. A drop of iodine was added on to the spotting tile. 9. After 20 minutes the boiling tubes were removed from the water bath and using a pipette a drop was withdrawn from each test tube and placed on the white tile containing the iodine solution. 10. The effect of the drop of liquid on the iodine was then noted. Change of color of the solution on the iodine solution. Mass of lead nitrate (±0. 01 grams)Color of the solution 0. 00Light Green 0. 10Light Green 0. 20Light Green 0. 30Dark Green 0. 40Darker Green 0. 50Dark Blue 1 2 3 4 5 6
Data processing: Iodine solution is used to test for starch. If starch is present in a substance then the iodine solution would turn blue black. If no starch is present then it remains as light brown. In the above experiment boiling tubes E and F contain starch. This was because they contained greater mass of lead nitrate and therefore has reduced the ability of the enzyme (amylase) to hydrolyse starch into maltose. The blue-black color remained indicating that the solution contained greater amounts of starch. In the boiling tube A the color was the lightest because lead nitrate was not present.
Thus the starch could bind to the active site of the amylase and could be broken down into maltose easily. Therefore in the test tube A starch was broken down in the solution and hence none was left. In boiling tubes B and C the solution was relatively darker because the mass of lead nitrate was greater but not great enough to stop the reaction completely. Therefore the greater the mass of lead nitrate, the darker the solution will form since a darker color indicated the presence of starch. The starch remained because of the effect of the inhibitor which reduced the capacity of the enzyme to break down starch into maltose.
Data Presentation. Thus the graph shows that a darker color perseveres if a greater mass of lead nitrate is added. This is because the bigger outcome of the inhibitor prevents the hydrolysis of the starch and so many molecules of starch still remain in the solution without being broken down by amylase. Therefore the color intensity of the solution and the mass of the lead nitrate share a direct relationship. Conclusion and Evaluation: Mass of lead nitrate added is directly proportional to the color intensity of the solution.
This is because a greater mass of lead nitrate reduces the ability of the amylase to breakdown starch into maltose. Therefore lead nitrate acts as a non-competitive inhibitor reducing the enzyme’s ability to catalyse the reaction. Lead nitrate is non-competitive because it affects the enzyme’s activity even though it is present in small quantities. The hypothesis were proven since the lead nitrate changes the shape of the active site of the enzyme and prevents some starch molecules from binding to the active site for catalysts. According to the results obtained from the experiment, my hypothesis is accepted and is correct.
My hypothesis was, “There is an inverse relationship between the mass of lead nitrate and the ability of amylase to convert starch into maltose. ” Despite the results obtained were correct and proved that the experiment was a success a few variables emerged during the performance of the experiment that if improved could result to a more accurate result. We didn’t have enough time to do this experiment over and over again so we didn’t have enough results to compare. Another important factor that may have influenced in our experiment was the quantity taken of the lead nitrate. We didn’t have any colorimeter so our result might not be accurate.