Enzyme Lab

Examination of how the concentration of substrate (H2O2) affects the rate of Enzyme Activity (Liver).

Sean Williams

Lab Partner: Jaemin Cho

IB Biology Standard Level

November 18, 2010

Introduction

        Enzymes are proteins produced by living things that operate as biochemical catalysts (speed up chemical reactions). These enzymes are formed from a sequence of amino acids that take on a specific three-dimensional structure.  Along this structure, there is a spot called the active site, where the substrate “matches” the shape of the site. An analogy can be used to explain this in the way that a lock and key are specific and match each other. Here, the lock is the enzyme’s active site while the key is the substrate.

        Substrate is the medium or surface that an organism attaches to.  This base or foundation is what the enzyme “works” on.  The substrate binds with the enzyme’s active site, and the enzyme catalyzes, leading to a chemical reaction.

Focused Problem

        I will investigate how the concentration H2O2 (substrate) will affect the rate of the enzyme-catalyzed reaction (liver).

→ This will be observed by placing a disk of liver into a test tube, and adding 5ml of H2O2 into the test tube. The rate of enzyme-catalyzed reaction will be observed by measuring how much water is displaced from the 100ml graduated cylinder, which is filled with water (placed in a water basin). The amount of water displaced is a result of the enzyme-catalyzed reaction. By using different concentrations of the substrate (H2O2), we are able to find out just how much a change in the concentration of substrate affects the rate of the enzyme-catalyzed reaction. Therefore, by finding out what concentration produces what results, we can apply this to instances where we may want to alter the rate of enzyme-catalyzed reactions to aid us in a way that is in our convenience.

Hypothesis

        The higher the concentration of substrate is, the faster (more water displaced) the rate of enzyme-catalyzed reaction will be. The lower the concentration of substrate is, the slower in the solution, the slower (less water displaced) the rate of enzyme-catalyzed reaction will be.

Independent Variable

        The concentration of substrate used to react with the enzyme. The H2O2, which is the substrate in this experiment, reacts with the liver, which is the enzyme in this experiment. Different concentrations of H2O2 are created by adding calculated amounts of water to the 30% concentration of H2O2 to create “weaker” concentrations.

We created a formula to better understand this process of creating different concentrations of substrate.  → [ ( Χ ∗ (Α/100) ) ∗ (100/Β) ] − Χ = Ζ

⇒         Χ = amount of H2O2                Α = original substrate %

B = desired substrate %         Ζ = amount of water added to the value Χ  

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Dependent Variable

        The rate of enzyme-catalyzed reaction will be observed by measuring how much water is displaced from the 100ml graduated cylinder. This measurement will determine how the concentration of the substrate affects the rate of enzyme-catalyzed reaction.  

Controlled Variables

Temperature

The temperature of the water was always held at a constant of room temperature (20 - 25°C). To make sure that the temperature would always stay the same, we placed our experiments at the same place where the same amount of sunlight was hitting. By keeping the experiment at the same place, we were able to keep the ...

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