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Enzymes

Introduction: "Enzymes are large biological molecules responsible for the thousands of chemical interconversions that sustain life. They are highly selective catalysts, greatly accelerating both the rate and specificity of metabolic reactions, from the digestion of food to the synthesis of DNA. Most enzymes are proteins, although some catalytic RNA molecules have been identified. Enzymes adopt a specific three-dimensional structure, and may employ organic (e.g. biotin) and inorganic (e.g. magnesium ion) cofactors to assist in catalysis." (Source: Wikipedia)

Data Table

Materials

  • 5 Clear plastic cups (9 oz)
  • 5 Small paper cups (3.5 oz)
  • 3% Hydrogen peroxide (H2O2)
  • Yeast
  • Raw potato
  • Raw chicken liver
  • Cooked chicken liver
  • Water

Procedure

  1. Place enough shredded potato into one of the clear plastic cups to later the bottom approximately 1 cm deep.
  2. Pour about 1/2 teaspoon of yeast into the second clear plastic cup.
  3. Place enough raw liver into the third clear plastic cup to layer the bottom approximately 1 cm deep.
  4. Place enough cooked liver into the fourth clear plastic cup to layer the bottom approximately 1 cm deep.
  5. Pour approximately 5 mL of water into the 5th plastic cup.
  6. Line up the 5 clear plastic cups in a row side-by-side. Fill each small paper cup with approximately 5 mL of hydrogen peroxide.
  7. Pour hydrogen peroxide from the paper cups into each clear plastic cup.  Observe and rank the level of activity (bubbling) in each cup on a scale from 1-5 (1= least active; 5 = most active).  Record your observations and rankings in the data table.  


Explanation: The purpose of this lab is to compare the enzyme content of different kinds of cells and to determine the effect of temperature on enzyme activity.  Most living cells contain an enzyme called catalase.  This enzyme changes a poison that accumulates in cells into harmless substances.  The poison is hydrogen peroxide and the resulting harmless substances are oxygen gas and water.  The reaction is:

2H2O2 -----> O2 + 2H2O

The substrate in this lab is the hydrogen peroxide, the enzyme is catalase, and the products are oxygen and water.  When the enzyme catalyzes the reaction that breaks hydrogen peroxide down, oxygen bubbles form.  Thus, the presence of bubbles indicates the presence of catalase, while an absence of bubbles indicates that no active enzyme is present.  

Questions & Answers: 

1. Which cell type contained the highest amount of enzyme?  Which cell type contained the least amount of enzyme?  How did you know how much enzyme was present in each cell type?

2. What effect did cooking the liver have on its level of enzyme activity?  Why?

3.  Cirrhosis of the liver is a disease which causes the liver to become thickened and "rubbery".  Hypothesize how enzyme function in the liver would be affected in a person with cirrhosis.


Applications to Everyday Life: 

1. High fevers are dangerous!  Although the increased temperature helps to kill bacteria in the body, a prolonged high fever will cause the body's enzymes to become denatured and lose function.

2. Cooking food is an example of protein denaturation.  Heating food at high temperatures causes the proteins in the food to change shape, which in turn makes it easier for us to digest!

3.  Hair straightening and curling irons work because heating the hair denatures its proteins.  The bonds between certain amino acids in the hair molecule are broken, changing the hair's texture.  Once the hair is wet, the original bonds are restored, therefore restoring the hair's texture.
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