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The Effects of pH, Temperature, Substrate Concentration, and Enzyme Concentration on Reaction Rates

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The Effects of pH, Temperature, Substrate Concentration, and Enzyme Concentration on Reaction Rates Abstract A class of proteins called enzymes catalyzes almost every chemical reaction in a cell. Enzymes increase the rates of reaction for those reactions, which are already energetically favorable, by lowering the activation energy. Quite often, the rate of an enzymatically catalyzed reaction is 106-1010 times that of an uncatalyzed reaction under similar conditions making it catalyzed reaction very favorable since it will essentially save time. The purpose of this experiment is to measure the rates of reaction of the enzyme peroxidase with the substrate guaiacol under varying conditions. To examine the effect of temperature on the reaction rate, the pH, substrate concentration, and enzyme concentration are held constant and reactions are carried out at different temperatures. Each enzyme has an optimal set of conditions at which the maximum reaction rate occurs. By carrying out the four separate experiments, the reaction rate was determined from the linear part of the absorbency versus time curve. The optimum temperature for an enzymatic reaction is 45?C and the optimum pH is 4. The more concentrated the substrate and enzyme buffer is, the fast its reaction rate will be. The buffer with the faster reaction rate is the most favorable. ...read more.


0.1050 6.0000 e-3 9 45 0.0570 0.1170 0.0980 0.1100 6.0000 e-3 10 50 0.0590 0.1220 0.1040 0.1150 7.0000 e-3 11 55 0.0600 0.1270 0.1100 0.1200 8.0000 e-3 12 60 0.0610 0.1310 0.1140 0.1230 7.0000 e-3 Figure 1. Effect of pH on reaction rate (500nm) Table 2. The Effects of Temperature on Reaction Rate (500 nm) Temperature Time Point Time (seconds) 25?C 35?C 45?C 55?C 1 5 0.0390 0.0490 0.0520 0.0440 2 10 0.0490 0.0630 0.0670 0.0510 3 15 0.0600 0.0740 0.0770 0.0570 4 20 0.0720 0.0850 0.0860 0.0600 5 25 0.0830 0.0930 0.0910 0.0590 6 30 0.0910 0.1000 0.0940 0.0600 7 35 0.0980 0.1050 0.0960 0.0580 8 40 0.1050 0.1070 0.0970 0.0560 9 45 0.1100 0.1100 0.0970 0.0550 10 50 0.1150 0.1120 0.0980 0.0540 11 55 0.1190 0.1140 0.0990 0.0520 12 60 0.1230 0.1150 0.0990 0.0520 Figure 2. Effect of Temperature on Reaction Rate (500nm) Table 3. The Effect of Substrate Concentration on Reaction Rate (500 nm) Substrate Concentration (mM) Time Point Time (seconds) 1.25 mM 2.5 mM 5 mM 7 mM 10 mM 20 mM 1 5 -0.0170 -7.0000 e-3 0.0380 0.0570 0.0670 0.1240 2 10 -0.0210 -2.0000 e-3 0.0420 0.0680 0.0860 0.1850 3 15 -0.0220 -2.0000 e-3 0.0480 0.0790 0.1050 0.2300 4 20 -0.0230 -1.0000 e-3 0.0550 0.0900 0.1220 0.2680 5 25 -0.0230 1.0000 e-3 0.0630 0.0990 0.1380 ...read more.


In the pH, substrate concentration, and enzyme concentration experiments, a direct relationship can be made between the absorbency and reaction rate. The buffer with the higher absorbency also has the faster reaction rate. The optimal temperature for enzymatic reactions is at 45?C. The least optimal temperature is at 55?C. The buffer at pH 4 had the fastest reaction rate making it the optimal pH for peroxidase. The least optimal pH would be at 8 since the graph was very flat and no reaction rate could be measured. The trend in the substrate and enzyme concentration data shows that the least concentrated buffers had the slowest reaction rates. The most concentrated buffers, 20 mM and 4 x 10-7 M, had the highest reaction rate. Since the reaction between the enzyme and buffer can occur very quickly, the delay between shaking the tube with parafilm, wiping the outside with a Kimwipe, and putting into the spectrometer could affect the results. The very first readings are important when calculating the slope. To improve the accuracy of the results, the experiment could be carried out for 2 or 3 minutes to observe the full reaction. In most of the graphs, the curve did not level out. This means the reaction was still occurring when we stop collecting data. Therefore, the slope was measure using all 12 points and the reaction rate might have been slower of faster depending on when the curve flat-lined. ...read more.

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