Enzyme Catalysis (Lab 2) Review
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| Link to the Enzyme Catalysis Lab
Activity Link to the Enzyme Catalysis Lab Activity Results Link to Lab Bench Lab Simulation Lab Two Review Essay Lab 2 Review PowerPoint (modified from pdf file posted by Glen Cochrane at Half Hollows High School)
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Some Key Review Concepts
Enzymes
Enzymes lower the activation energy necessary for a reaction to occur. The molecule that an enzyme acts on is called the substrate. In an enzyme reaction, substrate molecules are changed and a product is formed. The enzyme molecule is unchanged after the reaction, and it can continue to catalyze the same type of reaction over and over. Each enzyme is specific for the reaction it will catalyze.
Note: In this lab catalase is the enzyme. It will react with hydrogen peroxide (H2O2), the substate. The products formed should be water and oxygen.
H2O2 --catalase--> H2O + O2
Enzyme Structure
Enzymes are globular proteins. Their folded conformation creates an area known as the active site. The nature and arrangement of amino acids in the active site make it specific for only one type of substrate.
Even when different substrate molecules are present, only those that have the specific shape complementary to the active site are able to bind with the enzyme's active site.
When an enzyme binds to the appropriate substrate, subtle changes in the active site occur. This alteration of the active site is known as an induced fit. Induced fit enhances catalysis, as the enzyme converts substrate to product.
Factors influencing Enzyme Function
Two important influences are pH and temperature. When an enzyme's conformation is significantly altered because of pH or temperature variation, the enzyme may no longer catalyze reactions. An enzyme is said to be denatured when it loses its functional shape.
Lab Design
Overview & Adding Substances:
Investigate the rate at which the enzyme catalase converts
substrate to product by allowing catalase to react with hydrogen peroxide
for varying amounts of time and then stop the reactions by adding
To determine the amount of hydrogen peroxide that remains after the reaction, you will do a titration with KMnO4. In such a titration, you slowly add a chemical (KMnO4) that will cause a color change until a target color is achieved.
Add 10 ml of H2O2 to 7
different beakers, Label the 7 beakers, 0 sec (control), 10 sec, 30 sec,
60 sec, 120 sec, 180 sec, and 360 sec. Add 1 ml of catalase to each of the
beakers. Allow the reaction to occur for the time labeled on each of
the beakers. After the time has elapsed add 10 ml of
Titration:
To determine how much hydrogen peroxide (substrate) has been broken down by catalase at varying times, measure the amount of peroxide remaining in each flask.
To do so, slowly add KMnO4, which is purple, to the flask. The peroxide in the flask causes the KMnO4 to lose color when the solution is mixed thoroughly. When all the peroxide has reacted with KMnO4, any additional KMnO4 will remain light brown or pinkish even after you swirl the mixture. This is the endpoint. Record the amount of KMnO4 you have used. (The more KMnO4 you use, the more peroxide is in the flask.)
Analysis of Results
We can calculate the rate of a reaction by measuring, over time, either the disappearance of substrate or the appearance of product.