Ap Bio Lab 2 : Enzyme Catalysis

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Part I - Introduction

Enzymes are proteins that act as catalysts to regulate metabolism by selectively speeding up chemical reactions in the cell without being consumed during the process. During the catalytic action, the enzyme binds to the substrate – the reactant enzyme acts on – and forms an enzyme-substrate complex to convert the substrate into the product. Each type of enzyme combines with its specific substrate, which is recognized by the shape. In the enzymatic reaction, the initial rate of activity is constant regardless of concentration because the number of substrate molecules is so large compared to the number of enzyme molecules working on them. When graphed, the constant rate would be shown as a line, and the slope of this linear portion is the rate of reaction. As time passes, the rate of reaction slowly levels with less concentration of the substrate. This point where the rate starts to level is called the Kmax, in which the peak efficiency of enzymes is reached. In order to start the reaction, reactants require an initial supply of energy called activation energy. The enzymes work by reducing the amount of free energy that must be absorbed so that less required energy leads to faster rate of reaction.

The rate of catalytic reactions is affected by the changes in temperature, pH, enzyme concentration, and substrate concentration. Each enzyme has an optimal temperature at which it is most active; the rate of reaction increases with increasing temperature up to the optimal level, but drops sharply above that temperature. Most enzymes have their optimal pH value that range from 6 to 8 with exceptions, and they may denature in unfavorable pH levels. An increase in enzyme concentration will increase the reaction rate when all the active sites are full, and an increase in substrate concentration will increase the rate when the active sites are not completely full.

The enzyme used in this lab is catalase, a common catalyst found in nearly all living organisms. Catalse is a tetramer of 4 polypeptide chains, each consisting of more than 500 amino acids. Its optimum pH is approximately 7, and optimum temperature is about 37 °C. The primary catalytic reaction of catalase decomposes hydrogen peroxide to form water and oxygen as shown by the equation: 2 H2O2 → 2 H2O + O2 . Within cells, the function of catalase is to prevent damage by the toxic levels of hydrogen peroxide by rapidly converting them to less dangerous substances.

In this lab, we will show how catalase from 2 different sources (pure and potato extract) affects the rate of reaction by using titration to measure and calculating the decomposition rate of hydrogen peroxide (H2O2) to water and oxygen gas with enzyme catalysis.

Part II - Material and Methods
In Part 2A, I tested for catalase activity by using the seriological pipette to transfer 10mL of H2O2 into a beaker. The serological pipette was utilized in all transfer of substances in this lab because of its high quality and accuracy in measurement, especially with delicate control of volume and graduations that extend all the way to the top. Then, I used another serological pipette to add 1mL of catalase in the beaker. After observation, I analyzed and recorded the results. The above procedure was repeated with the boiled catalase solution using another beaker and serological pipette. I analyzed and recorded the results after examination.

In Part 2B, I established the baseline to determine the amount of H2O2 present in the nominal solution without adding the enzyme. I used serological pipettes (for the same reason mentioned above) to transfer 10mL of H2O2 in a beaker previously labeled as baseline and 1mL of distilled H2O into the same beaker after that. Next, I added 10mL of 1.0M H2SO4 into the beaker and mixed the solution by gently swirling the beaker. The sulfuric acid was used to lower the pH and thereby stopping the catalytic activity. Using the serological pipette, I removed...
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