The Effects of pH on the Breakdown of Hydrogen Peroxide by the Enzyme Catalase Derived from Brocco

The Effects of pH on the Breakdown of Hydrogen Peroxide by the Enzyme Catalase Derived from Brocco

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The Effects of pH on the Breakdown of Hydrogen Peroxide by the Enzyme Catalase Derived from Broccoli ( Brassica oleracea var. italica ) Lab TA: Ali McGregor Megan Lawless Date of Lab: 9/14/07
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Enzymes are catalytic proteins that speed up chemical reactions without being consumed by them (Campbell and Reece 2005). The small portion of an enzyme that binds to a reactant, known as the substrate, is called the active site (Campbell and Reece 2005). The size, shape, and composition of the active site determine what substances the enzyme will bind to (Campbell and Reece 2005). When a substrate enters the active site, chemical interactions between the enzyme and the substrate cause a change in the conformation of the enzyme that leads to an even better fit (Campbell and Reece 2005). This process is known as induced fit, and is another effect of the complementary physical and chemical relationship between substrate and active site (Campbell and Reece 2005). Enzymes speed up reactions by lowering the activation energy needed for a reaction to occur (Campbell and Reece 2005). Activation energy is the amount of energy that must be absorbed by the reactants in order to reach an unstable state (Campbell and Reece 2005). It is in this unstable state that the bonds can be broken and the new bonds of the product can be formed (Campbell and Reece 2005). Enzymes can lower the activation energy in one of several ways. One way is for the enzyme to orient the reactants properly so that they reaction between them can occur (Campbell and Reece 2005). A second way is for the enzyme to stress and bend chemical bonds in the substrate that must be broken (Campbell and Reece 2005). Enzymes can also work by creating a microenvironment that is more favorable for the reaction (Campbell and Reece 2005). Lastly, enzymes sometimes directly participate in reactions by covalently bonding to the substrate briefly (Campbell and Reece 2005). There are several different factors that can effect the functioning of an enzyme. As temperature increases, the rate of a catalyzed reaction will increase up to an optimal temperature because of an increase in enzyme-substrate collisions (Campbell and Reece 2005). Above this
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optimal temperature, the enzyme will denature due to the breaking of hydrogen and various other bonds (Campbell and Reece 2005). Enzymes respond similarly to changes in pH. There is a pH at which an enzyme functions best, and as the pH changes above or below this optimal pH, the rate of the reaction will decrease (Campbell and Reece 2005). As enzyme concentration increases, the rate of the chemical reaction also increases until the enzyme becomes saturated (Campbell and Reece 2005). At the saturation point, all of the active sites are filled with a substrate, and the only limiting factor is how quickly the enzyme can convert the substrate to the products; this is known as the turnover rate (Hardy, Campbell, and Plescia 2007). The situation is very similar with an increase of substrate concentration.
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