What does pepsin do to egg whites?


Procedure

1. Predict the effect pepsin will have on egg white and how you will be able to tell.

2. Label 8 small test tubes (10 mL size) 1 through 8.

3. Prepare the tubes as outlined in Table 1. Use a piece of egg white small enough to fit inside the tube and try to make the pieces of egg white and potato the same size. Once you have the egg white and potato, slice each into four or five smaller pieces.


Table 1. Preparation of the tubes

Tube

Solution

Food

tube 1 & 2

5 mL water

-

tube 3 & 4

2.5 mL water + 2.5 mL 0.2% hydrochloric acid

egg

tube 5 & 6

2.5 mL 1% pepsin + 2.5 mL 0.2% hydrochloric acid

egg

tube 7 & 8

2.5 mL 1% pepsin + 2.5 mL 0.2% hydrochloric acid

potato

4. Vortex the tubes to mix the contents thoroughly.


5. Leave the odd numbered tubes at room temperature and place the even numbered tubes in the incubator at 37oC.


6. Let the tubes incubate overnight. Observe the tubes the next day and record your observations.



Questions

1. a) Describe the appearance of the egg white and the liquid in tubes 1-6. Account for any differences by explaining the specific effect pepsin is having on the egg white?(digesting into smaller proteins)

b) Do these results support or refute your prediction?

2. a) Why were tubes 1/2 and tubes 3/4 used?

b) Why was egg white used? (contains the protein albumin)

3. a) Why was the experiment performed at two different temperatures? (shows the effect of humanbody on the process)

b) Describe and explain the effect, if any, of temperature. Was this expected?

4. Which test tube most closely resembles the conditions in the human digestive system? (tubewith pepsin + acid at 39oC)

5. What do you think happened in tubes 7 and 8.