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How Does the Shape of Protein Molecules Affect their Chemical Behavior

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Author: Janice VanCleave

Protein molecules are vital to life. They are the molecules that provide the very shape of our bodies.

In this project, you will learn about the shape of protein molecules and the effect of their shape on their chemical behavior. You will analyze different methods of denaturing, the process by which the sizes or shapes of the protein molecules are changed. You will also look at the bonding between the protein molecules of curly hair and of straight hair and determine methods of changing the bond.

Getting Started

Purpose: To demonstrate the denaturing of gelatin (a protein) with an acid.

Materials

  • 3-ounce (85-g) packet of flavored gelatin
  • 6 3-ounce (90-ml) paper cups
  • refrigerator
  • 1/4 teaspoon (1.2 ml) of meat
  • tenderizer
  • spoon
  • marking pen
  • masking tape
  • cereal bowl

Procedure

  1. Prepare the flavored gelatin by following the instructions on the packet.
  2. Pour equal amounts of the prepared gelatin into the six paper cups.
  3. Place four of the cups in the refrigerator for use in later experiments.
  4. Allow the two remaining cups to sit at room temperature for 30 minutes.
  5. Add the meat tenderizer to one of the two remaining cups and stir well.
  6. With the marking pen, write "Meat Tenderizer" on a piece of masking tape and tape this label to the cup.
  7. Label the second cup "Gelatin."
  8. Place the labeled cups in the refrigerator overnight (see Figure 9.1).
  9. Remove the two labeled cups from the refrigerator.
  10. Tilt the cups horizontally over the bowl.
  11. Observe the fluidity (ability to flow) of the contents of each cup.

Results

The warm liquid in the cup labeled "Gelatin" changes into a semisolid, quivering mass when chilled. The gelatin containing the meat tenderizer does not become firm; it remains a liquid.

Why?

Proteins are large chains of amino acids joined together. These macromolecules often contain thousands of amino acids. The long protein molecules in the gelatin dissolve in hot water and form a colloidal mixture (solution with large solute molecules suspended throughout). The gelatin (protein) molecules are forced apart and are surrounded by water molecules. As the solution cools, chemical bonds form between the protein molecules. The bonds between the protein molecules produce a lattice network in which water molecules in the solution become trapped; thus, the solution "gels" into a firm, jellylike substance.

Enzymes are chemicals that cause specific chemical reactions to occur. The meat tenderizer contains an enzyme that breaks large protein molecules into smaller molecules. (When used on meat, the tenderizer thus makes the meat easier to chew.) In the gelatin, the smaller molecules formed during this denaturing process do not form a network of bonding; thus, the solution does not gel.

Try New Approaches

  1.  
    1. Meat tenderizers contain the same enzyme that is found in fresh pineapples, or one similar to it. Repeat the experiment replacing the meat tenderizer with 1 teaspoon (5 ml) of fresh chopped pineapple.
    2. Canned pineapples are heated during the canning process. Repeat the previous experiment replacing the fresh pineapple with canned pineapple. Does heat change enzymes and cause them to not function properly?
  2.  Proteins: Changed by Denaturing

  3. Does heat affect the ability of enzymes to denature proteins? Repeat the original experiment placing the meat tenderizer in the boiling water used to prepare the gelatin. Boil the water for several minutes before adding it to the gelatin.
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