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The Effect of pH on Enzymatic Reaction Rate Essay

Abstract
Enzymes are affected by changes in pH. The most favorable pH value— the point where the enzyme is most active—is known as the optimum pH. This experiment was conducted to determine the effect of pH reaction rate on an enzyme, catalase, from yeast. The experimental results indicate that the catalase worked best at a neutral pH level of seven (7). Introduction

An enzyme is a protein molecule that serves as a catalyst. “The basic function of an enzyme is to increase the rate of a reaction; most cellular reactions occur about a million times faster than they would in the absence of an enzyme” (Ophart, 2003). The enzyme is not changed by the reaction because the enzyme temporarily binds to the reactant molecule known as the substrate (Prezler et al., 2012). Enzymatic activity primarily depends on its environmental conditions such as pH, substrate concentration, and temperature (Prezler et al., 2012). In this case we tested the enzymatic activity at different levels of pH. The focus of this experiment was the activity of an enzyme that catalyzes the reduction of hydrogen peroxide known as catalase. “Catalase is a common enzyme found in nearly all living organisms that are exposed to oxygen, where it functions to catalyze the decomposition of hydrogen peroxide to water and oxygen” (Princeton, N.D).

Without catalase present in our body, the hydrogen peroxide can accumulate and become toxic to our cells. Therefore, the environment that surrounds catalase, such as pH, must not be too extreme because it may cause the enzyme to denature or lose its function. The hypothesis of this experiment is that denaturing, or loss of function, occurs in catalase when surrounded by acidic or basic solutions. To test this hypothesis, we used yeast cells containing catalase and mixed the yeast cells with solutions containing different pHs (acidic, basic, and neutral). A filter paper was placed into a test tube containing hydrogen peroxide to indirectly measure the different reaction rates by timing the oxygen production. It was predicted that the reaction taking place in the acidic and basic solutions would have a slower reaction rate due to enzyme denaturing, as opposed to the filter paper that was mixed with the neutral pH solution. Methods

First, the instructor prepared the yeast cells containing catalase using distilled water and heat in an Erlenmeyer flask. The yeast was mixed into three separate solutions. The first solution was acidic with a pH of two (2), the second solution was neutral with a pH of seven (7), and the third solution was basic with a pH of ten (10). Five (5) mL of yeast cells and five (5) mL of the acidic solution were mixed together creating a fifty percent concentration of yeast cells. Five (5) mL of yeast cells and five (5) mL of the neutral solution were mixed together creating a fifty percent concentration of yeast cells. Five (5) mL of yeast cells and five (5) mL of the basic solution were mixed together creating a fifty percent concentration of yeast cells. Six (6) test tubes—divided into two trials—were filled with nine (9) mL with a .3% of hydrogen peroxide and six (6) pieces of filter paper were hole-punched. For five (5) seconds the six (6) pieces of filter paper were stirred into the acidic, neutral, or basic solutions that contain the fifty percent concentration of yeast cells.

The six (6) filter pieces of paper containing yeast catalase are then dropped into the six (6) different test tubes filled with hydrogen peroxide. A timer is used to measure how long the filter paper containing catalase will rise from the bottom of the test tube to the top of the test tube due to the production of oxygen. The independent variable in this experiment is each beaker containing the different pH values and it was manipulated by having the three different levels of pH (acidic, neutral, and basic). The dependent variable is the reaction rate in which was measured by timing the production of oxygen trapped under the paper. Results

The experimental results indicate that the catalase works best at a neutral pH of seven (7) as evidenced by the quickest reaction times of 3.15 seconds and 3.56 seconds. The acidic solution with a pH of two (2) slowed down the reaction rate significantly as compared to the pH of seven (7). We didn’t observe a significant difference between the basic solution and the neutral solution although the pH of ten (10) did slow down the reaction rate. In both trials, the reaction rate of the yeast cells mixed with a solution with a pH of two (2) was consistently slower than the basic and neutral solutions. As hypothesized, the results clearly show that enzymatic reaction was slowed down in both acidic and basic environments. The observed data from the experiment is shown on table 1 and the “effect of pH on reaction time” graph.

Discussion
“Enzymes are required for your body to function properly because without enzymes you wouldn’t be able to breathe, swallow, drink, eat, or digest your food” (Enzymes Essentials, N.D). This experiment was conducted to determine the effect of pH reaction rate on an enzyme, catalase, from yeast. The predicted results indicated that the reaction that takes place in the acidic and basic solutions would have a slower reaction rate, as opposed to the reaction that was mixed with the neutral solution. The experimental results indicate that the catalase works best at a neutral pH of seven (7). Overall, the results of this experiment support the hypothesis that denaturing, or loss of function, occurs in catalase when surrounded by acidic or basic solutions. The acidic solution with a pH of two (2) might have denatured the catalase almost completely resulting in the reaction time being significantly slower than both the neutral and basic solutions.

The basic solution of pH of ten (10) was slowed down a little more than the neutral solution, although, there could have been a human error in timing the reaction rate due to the three different stop watches and the three different timers recording each trial. The conclusion that denaturing, or loss of function, occurs in catalase when surrounded by acidic or basic solutions has a number of implications. Our body is constantly metabolizing which creates an extreme number of hydrogen peroxide; therefore, if the cell environment is either too acidic or too basic, the action of catalase can be inhibited which can cause the hydrogen peroxide to destroy our cells. In addition to catalase, there are also many enzymes that are the most efficient when surrounded by a pH of 7. However, there are some enzymes such as pepsin, who work under acidic environments (Biochemistry Lab Manual, 2003). The environment that surrounds our enzymes is extremely important when it comes to the processes of our body because the environment can inhibit many reactions that are necessary for proper homeostasis.

References
Biochemistry Lab Manual. 2003. pH Effects on Enzyme Activity. Retrieved February 11, 2014 from http://www.chem.fsu.edu/chemlab/bch4053l/enzymes/activity/index.html

Enzymes Essential. (N.D). Enzymes Basics. Retrieved February 3, 2014 from http://www.enzymeessentials.com/HTML/print_tour.html

Ophart, C.E. 2003. Enzyme Characteristics. Retrieved February 3, 2014 from http://www.elmhurst.edu/~chm/vchembook/570enzymes.html

Preszler, R.W., Haas, L.L., Marion, A.L., Urquidi, L.J. 2012. Cellular and Organismal Biology: Student Investigations, 10th edition, Hayden-McNeil
Publishing, Plymouth MI

Princeton. (N.D). Catalase. Retrieved February 3, 2014 from http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Catalase.html


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