How Does the Shape of Protein Molecules Affect their Chemical Behavior (page 2)

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Author: Janice VanCleave

Design Your Own Experiment

  1. Can the protein be denatured once the protein network has formed? Use the four congealed cups of gelatin made in the original experiment. Sprinkle 1 teaspoon (5 ml) of meat tenderizer on the surface of the gel in one cup; use a different brand of tenderizer in the second cup. In the third cup, place 1 teaspoon (5 ml) of chopped fresh pineapple; in the fourth cup, choose any fresh fruit, such as a banana or an apple. Store the gelatin cups in the refrigerator overnight. Observe the surface of each cup for indications that the solid gel has liquefied.
  2. Hair is made of long chains of protein molecules. These chains of molecules are called polymers. The protein molecules in hair line up, with chemical bonds connecting the molecules like steps on a ladder. There are two types of bondings that form the steps of this ladderlike structure. One bond is a connection between two sulfur atoms, one from each adjacent protein molecule. Sulfur-to-sulfur bonds are very strong. The other bond, a hydrogen bond, is weaker. In straight hair, the protein molecules lie straight, with the bonds linking them together. But in curly hair, the protein molecules are looped around, with the bonds holding them in place. To change the shape of hair, bonds have to be broken, the hair reshaped, and new bonds formed. Heat is one way of temporarily changing the hydrogen bonding in hair protein.
    1. Choose a helper with straight hair. Wrap a lock of your helper's straight hair around a heated curling iron for the amount of time indicated in the iron's instructions. Take before and after photographs of the hair for display.
    2. Choose a helper with curly hair. Straighten a lock of hair by asking your helper to hold a lock of his or her hair as straight as possible while you apply heat with a hair dryer as described in the dryer's instructions (see Figure 9.2). Again use before and after pictures to display the results.
  3. A change of the hydrogen bonding in the hair protein lasts until the hair is wet; the proteins then return to their natural position. For a more permanent change, chemicals have to be used to break the sulfur bonds, the hair reshaped, and new sulfur bonds formed. A "permanent" is a procedure used to curl hair. First, a chemical is used to break the sulfur and hydrogen bonds. Then, a second chemical, the neutralizer, is used to stop the bonds from breaking and allow new bonds to form, thus holding the hair in its new shape even after wetting. Demonstrate the changes made by the chemicals of permanents by collecting samples of hair from a cosmetologist. Follow the instructions in a commercial home permanent kit to curl these hair samples.

Get the Facts

  1. The term protein was introduced by Gerardus Mulder. This nineteenth- century Dutch chemist and physician believed that protein was of prime importance to the functioning of the body and to life itself. Find out more about the scientist who contributed to our understanding of protein molecules' chemical composition, sources, and functions. Also look for information about Frederick Sanger's analysis of the protein called insulin.
  2.  Proteins: Changed by Denaturing

  3. Hydrogen bonds are not true bonds because there is no transfer or sharing of electrons. Use a chemistry text to find out more about the connection called hydrogen bonding.
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