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Digestive Enzymes

Robert Goodman

Introduction
Enzymes make the body go! They are proteins which are made by the cell and which act as catalysts. Catalysts speed up chemical reactions. "Speed up" is, in a sense, an understatement. Without these catalysts, chemical reactions would take place so slowly that it would be as if they weren't taking place at all.

Most enzymes do their work in the cell. Others are produced by the cell but released to do their job elsewhere. Such is the case with the enzymes we will study today. Salivary amylase (also known by its' code name-ptyalin) is produced by cells in the salivary glands and released, through ducts, into your oral cavity. Pepsin is produced in the gastric glands and released through ducts into your stomach. Let's see what they do.

Materials

    Test Tube Rack
    Boiling water bath
    3 100 mL Graduated Cylinders
    Warm Water Bath
    3 Test Tubes
    Test Tube Holder
    4 Plastic Sandwich Bags
    4 Rubber Bands
    Funnel
    Marking pencil
    4 250 mL beakers
    Pepsin solution
    Starch Solution
    Benedict's Solution
    4 Stirring Rods
    Distilled Water
    Metric Ruler
    Food Samples
    Hydrochloric Acid
    Nylon thread
    Thermometer
    Incubator

Procedure
  1. PEPSIN (Work in Groups of 4)
    • Make an artificial stomach by placing a plastic sandwich bag inside a 250 mL beaker. Secure it with a rubber band over the lip of the beaker (see diagram below). Repeat this procedure three times so that you have 4 artificial stomachs. Label them: 1, 2, 3 and 4.

    • Follow the flow chart below in adding the appropriate amounts of each solution to each stomach. Use graduated cylinders for measuring fluid volumes.


      Stomach 1Stomach 2Stomach 3Stomach 4
      Water 80 mL40 mL40 mL0 mL
      HCl0 mL0 mL40 mL 40 mL
      Pepsin0 mL40 mL0 mL40 mL

      Keep each "stomach" in the the 40o C water bath for the duration of the laboratory, but place them in the 40o incubator just before you leave.

    • Collect 4 small, equal size morsels of each the following foods:
      Hard boiled egg white
      Bread
      Beef Jerky
      Potato

    • Tie a small length of nylon thread to each piece of food. The thread should be long enough to suspend and periodically remove each morsel of food.

    • Suspend the 4 kinds of food in each of the stomachs.

    • Observe the suspended food after 15 minutes, 30 minutes, 45 minutes and 24 hours.

    Q-1) Record your observation on a data table provided.

    Q-2) Stomach #4 is intended to simulate the conditions of your stomach. Why was it necessary to set up each of the other three stomachs? Consider the importance of each one separately.

  2. SALIVARY AMYLASE (Work in Groups of 2)
    • Number your test tubes 1, 2 and 3 and also place your initials on each tube (Do it toward the top of the tube.). Make small marks on each test tube about 1 and 2 cm from the bottom.

    • Follow the flow chart below in adding the appropriate amounts of each solution to each test tube. Use a funnel to collect the saliva. Do not count bubbles in the measurement. Carefully wash the funnel with soap and water after collecting the saliva.

      Tube 1 Tube 2 Tube 3
      Water 1 cm 1 cm 0 cm
      Saliva 1 cm 0 cm 1 cm
      Starch 0 mL 1 cm 1 cm

    • Place the test tubes in a warm water bath (37oC) which is on the front desk---NOT the boiling water bath which will be used for the Benedict's test later. Leave the tubes in the warm water for 10-15 minutes.

    • Perform the Benedict's test on all three tubes. Place 20 drops of Benedict's solution in each test tube and place them in the boiling water. Wash the test tubes with soap and water after you are finished.

      Q-3) Record your results.

      Q-4) What do the results tell you about the contents of each test tube?

      Q-5)If you got a positive Benedict's test in one of the test tubes, why was it also necessary to do the Benedict's test on the other two?

Review Questions:

  1. The gastric glands of the stomach secrete pepsin and hydrochloric acid. What prevents this gastric juice from digesting itself?

  2. Recently medical dogma regarding the cause of ulcers has changed. What was the "old view" and what is the "new view" to account for ulcers?

Conclusion: The "Pepsin" component of this lab is modified from "Looking Into The Stomach", Flinn Scientific, Inc. Batavia, Ill Biolabs¬ ©1992 BSCS.

Data Table-Pepsin Experiment:

Stomach 1Hard Boiled Egg WhiteBeef JerkyBreadPotato
15 Minutes
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30 Minutes
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45 Minutes
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24 Hours
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Stomach 2Hard Boiled Egg WhiteBeef JerkyBreadPotato
15 Minutes
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30 Minutes
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45 Minutes
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24 Hours
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Stomach 3Hard Boiled Egg WhiteBeef JerkyBreadPotato
15 Minutes
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30 Minutes
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45 Minutes
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24 Hours
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Stomach 4Hard Boiled Egg WhiteBeef JerkyBreadPotato
15 Minutes
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.
30 Minutes
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.
45 Minutes
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.
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.
24 Hours
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.
.

Data Table-Amylase Experiment


Tube 1Tube 2Tube 3
Benedict's Results
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