-Advertisement-


Enzyme Labs Using Jello

Anne McDonald and Michael O'Hare
1991 Woodrow Wilson Biology Institute


OBJECTIVE:

To test for the presence of enzymes in fruit and the specificity of those enzymes, as well as to identify and show the susceptibility of enzymes to certain environmental factors (temperature and pH) originating in the enzyme's environment.

BACKGROUND:

Most students have eaten Jello and may have made some themselves. They may have noticed a warning in the directions NOT to add fresh pineapple or kiwi to the mixture. Doing so will cause the gelatin to remain in the liquid state, even after prolonged refrigeration. This is due to the presence of certain proteolytic enzymes in the fruit which digest or denature the protein molecules present in the gelatin.

SAFETY CONSIDERATIONS:

The use of goggles is recommended, as well as proper precautions against fire and strong acids or bases.


LAB I: What Fruits Contain Enzymes that Digest Protein?

MATERIALS:

Per Group:
  • 1 envelope Knox gelatin
  • 1 measuring cup
  • 9 test tubes
  • 1 test tube rack
  • 7 - 5 ml pipettes
  • 1 spoon

Per class:

  • Boiling water
  • Cold water
  • 2 measuring spoons
  • Adolph's meat tenderizer solution*
  • French's meat tenderizer solution*
  • pureed FRESH fruit with juice filtered from pulp (or frozen juice concentrate, thawed):
    • pineapple
    • apple
    • kiwi fruit
    • papaya
    • orange
    • fig
  • refrigerator
* Mix 1 tablespoon tenderizer into 1 cup of warm water and stir well.

PROCEDURE:

  1. Number test tubes from 1 - 9.
  2. Prepare gelatin in measuring cup using only half of the recommended boiling and cold water amounts given in the package directions. Stir well with spoon until all gelatin is dissolved.
  3. Place 3 ml of the designated fruit juice into each test tube. **Use a separate pipette for each fruit. Failure to do so may result in mixing of juices and inaccurate results!
    • tube 1 - water only
    • tube 2 - pineapple
    • tube 3 - kiwi
    • tube 4 - orange
    • tube 5 - apple
    • tube 6 -- papaya
    • tube 7 -- fig
    • tube 8 -- Adolph's solution
    • tube 9 -- French's solution
  4. Add 10 ml. gelatin mixture to each test tube. Shake well to ensure proper mixing.
  5. Refrigerate test tubes overnight.
  6. On day 2, check the contents of each test tube for solidification of the contents. Record the observations.

ANALYSIS:

Those mixtures that remained liquid provide evidence that protein has been digested. The solidified gelatin was not digested.

  1. Identify the control of the experiment (WATER), the positive results (PINEAPPLE, KIWI, PAPAYA, FIGS, ADOLPH'S, AND FRENCH'S), and the negative results (APPLE, ORANGE).
  2. Read the ingredients labels of the meat tenderizers. What enzymes do they contain? What is the enzyme source of each? Consider WHY these products are used to tenderize meat.
  3. Other than sanitary reasons, can you think of a second reason why pineapple processors are required to wear gloves and surgical masks? (TO PREVENT PRESENCE OF ENZYME ON SKIN AND LUNGS WHICH MAY DESTROY BODY TISSUE.)


LAB II: What Effect Does Temperature Have on Enzyme Action?

BACKGROUND:

An enzyme's function is related to the 3-dimensional structure of it's molecule. This structure can be altered by heat, thus causing the enzyme to lose its normal function. In Lab II, students will test the effect of temperature on the ability of the proteolytic enzyme bromelein (found in pineapple) to digest gelatin.

MATERIALS:

Per group:
  • 1 pkg. Knox gelatin, prepared according to procedure in LAB I.
  • 11 test tubes
  • 1 test tube rack
  • 2 - 5 ml pipettes
  • water bath
  • thermometer
  • hot plate

Per class:

  • frozen pineapple juice concentrate, thawed
  • boiling water
  • cold water
  • ice bath
  • several containers for cool water bath, if desired by students in their experimental design
  • refrigerator

PROCEDURE:

  1. Number test tubes from 1 - 10. Label the remaining tube as "RT" (room temperature).
  2. Each group will design their own temperature gradient ranging from 0 C to 100 C and will record the test tube numbers and corresponding test temperatures assigned for each. Record the temperature of the room for test tube "RT."
  3. Add 3 ml pineapple juice to each tube.
  4. Heat (or cool) each test tube to the appropriate temperature as decided upon in Step 2. Leave test tube "RT" at room temperature. (Hint: start with all tubes in cool water in the water bath, and gradually increase the temperature, withdrawing the numbered test tubes in order as the a appropriate temperature level in the bath is reached.)
  5. Add 10 ml gelatin to each tube. Shake well to ensure proper mixing.
  6. Refrigerate test tubes overnight.
  7. On day 2, check each test tube for liquidity of the contents. Record observations.

ANALYSIS:

  1. At what temperature were the first signs of liquidity observed?
  2. What do you conclude about the temperature at which bromelin's molecular structure is altered?


LAB III: What Effect Does pH Have on Enzyme Action?

BACKGROUND:

Extremes in pH levels, like temperature, cause alterations in the structure, and thus the function, of enzyme molecules. Also, varying concentrations of pH levels in solution affect the activity of the enzyme. In Lab III, students working in groups will test the effect of different concentrations of an acid (HCl) or a base (NaOH) on the activity of the proteolytic enzyme, bromelin.

MATERIALS PER GROUP:

(Group A will need 1 ml HCl, Group B will need 1 ml NaOH)
  • 21 test tubes
  • 10 ml graduated cylinder
  • 10 - 5 ml pipettes
  • refrigerator
  • test tube rack
  • water
  • 30 ml frozen pineapple juice concentrate, thawed
  • 1 pkg Knox gelatin, prepared according to procedure in LAB I.

PROCEDURE:

  1. Group A: label 10 test tubes A-1, A-2, A-3, etc. up to A-10.
    Group B: label 10 test tubes B-1, B-2, B-3, etc. up to B-10.
  2. Place 3 ml pineapple juice into each of the labeled test tubes.
  3. Place 9 ml water into the 10 empty test tubes. Label one of these tubes as CONTROL and set it aside.
  4. Make a serial dilution in the 9 test tubes by following the dilution table drawn below.
    Group A use HCl, Group B use NaOH. *** Use a different pipette for each dilution .
  5. Transfer 3 ml of diluted pH concentrations into each test tube of pineapple juice, using the dilution table below as a guide. Record the concentration of solution placed in each test tube. (Example: A-1 = 1:1 dil, A-2 = 1:10 dil, A-3 = 1:100 dil, etc.) The solution concentrations become weaker as the test tube numbers progress from 1 - 9.
  6. Transfer 3 ml of water from CONTROL tube into tube A-10 (or B-10).
  7. Add 10 ml gelatin to each test tube, A-1 to A-10 (or B-1 to B-10). Shake well being careful not to let the acid or base come into contact with skin.
  8. Refrigerate test tubes overnight.
  9. On day 2, check each test tube for liquidity of the contents. Record observations.

ANALYSIS:

  1. At what concentration of acid or base was the first signs of liquidity observed?
  2. What conclusion can be derived as to the acid/base concentration at which bromelin's molecular structure is altered?


Woodrow Wilson Index


Activities Exchange Index


 
Custom Search on the AE Site

 

-Advertisement-