Effects of Changes in Physical Properties on Enzyme Activity

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Effects of Changes in Physical Properties on Enzyme Activity By
Alex Hoffmann

First Individual Lab Report
Wednesday 7:30-10:15pm
10/24/12
Meghan Duell

Abstract
The goal of this lab was to determine the effects of certain physical properties on enzyme activity. Enzyme activity was measured by the height of the bubbles that appeared after the enzyme was added which are proportional to the rate of the reaction when time is constant. The fact that enzyme activity is affected by physical properties such as temperature, substrate concentration, and pH is clearly supported by my data, but the specific effects of these physical properties are not clear. My predictions varied from my results and can mostly only be explained by error. Introduction

Enzymatic activity can be manipulated by changes in physical properties. Changes in heat, pH, and salt concentration can all have effects on the rate of enzyme activity (Farzin, 2012). Enzymes “catalyse the dismutation of hydrogen peroxide to oxygen and water (2H2O2 → 2H2O + O2)” which is the cause of the bubbles that can be observed and measured (Obinger, 2012). The output of oxygen occurs very rapidly when the reaction begins and bubbles appear quickly and clearly which serve as a very good form of measurement of enzyme activity (George, 1947). In a reaction in which an enzyme is involved, several steps occur. First, an enzyme-substrate complex is formed when the enzyme and substrate molecule bind together. The enzyme later releases the molecule as a product. This process can be viewed as an equation where E is the enzyme, S is the substrate, and P is the product: E + S → ES → E + P (Sadava et al., 2010). Changes in physical properties like those that were tested: temperature, substrate concentration, and pH will sometimes increase or decrease this occurrence. Materials and Methods

In Experiment One I varied the temperatures of four separate samples of hydrogen peroxide in order to test the effects of temperature on enzyme activity. To do this, I began with one test tube filled with 3 mL of hydrogen peroxide. I placed the test tube in an ice water bath to lower the temperature. Once the thermometer showed that the temperature had reached 0⁰C, I removed it from the ice bath and put it in the test tube rack. I then added 3 mL of catalase and set the timer for 60 seconds. After the 60 seconds had passed, I used a wax pencil to mark then a ruler to measure the height of the bubbles within the tube and I recorded my results. Next, I filled another test tube with 3 mL of hydrogen peroxide and placed it into room temperature water until the temperature read 37.4⁰C and again, I added the catalase after placing it in the test tube rack and measured the height of the bubbles after 60 seconds. I did the same for a third test tube, only I placed it into boiling water and waited until the temperature read 50⁰C to add the catalase, and finally a fourth test tube was also placed into boiling water until it reached 70⁰C. Temperature was my independent variable since I tested four different temperatures: 0⁰C, 37.4⁰C, 50⁰C, and 70⁰C. My dependent variable was the rate of enzyme activity, which I recorded by measuring the heights of the bubbles. There were no positive or negative controls, but other controls included: 3 mL of hydrogen peroxide and catalase added to each test tube, enzyme concentration, substrate concentration, and pH. In Experiment Two I varied the substrate concentrations of four samples to test its effect on enzyme activity. I formed four solutions by calculating the amounts of hydrogen peroxide and distilled water I needed to mix to create a 1%, 1.5%, 2%, and 3% saturated solution. Using the (P1)(V1)=(P2)(V2) formula and by knowing that the hydrogen peroxide used had a 3% substrate concentration, I discovered the amounts of each that was needed to make a 3mL solution. My first test tube consisted of 1 mL hydrogen peroxide and 2 mL of water to make a...
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