Chemical Aspects of Digestion:

                               Demonstration of Enzyme Activity

 

I.  Digestion of protein:

            A.  Preparation:

           

                        1.  In each of two test tubes, labeled #1 and #2, place equal amounts of protein material provided by your instructor.

 

                        2.  Add 5 ml of distilled water to tube #1.

 

                        3.  Add 5 ml of 5% pancreatin solution to tube #2.

 

                        4.  Put tubes #1 and #2 in the incubator at 40º C for about 1½ hours.

 

            B.  After incubating, add several eye droppers-full of Biuret solution to each tube until the color of the tube is either pink or purple.  A pink color change indicates the presence of peptides.  A purple color change indicates the presence of protein.  Which tube shows an indication that the chemical digestion of protein has occurred?

 

 

            C.  What pancreatic enzymes are responsible for beginning the digestion of protein?

 

 

D.    Why did the contents of tube #1 turn purple?

 

 

E.     Considering this demonstration of protein digestion:

1.       Which tube is the “control”?

2.      Which tube is the “experiment”?

 

 

II.  Digestion of emulsified fat:

            A.  Preparation:

 

                        1.  Pour 5ml of a mixture of milk and litmus solution into each of two test tubes marked #3 and #4.

 

                        2.  Add 2 ml of 5% pancreatin solution to tube 3.

 

                        3.  Put tubes #3 and #4 in the incubator at 40º C for about 1½ hours.

 

            B. After incubating, look at the color of each tube.

1.  What is the color of tube 3?

                       

                        2.  What is the color of tube 4?

 

C.    What is the purpose of using litmus in this experiment?

 

D.  What is the purpose of using milk in this experiment?

 

            E.  What substances caused the color change seen in tube 3?

 

            F.  Although not indicated by the color change in tube 3, what is another end- product of fat digestion?

           

G.     What is the pancreatic enzyme responsible for the digestion of fat?

 

H.      Considering this demonstration of the digestion of emulsified fat:

1.      Which tube is the “control”?

2.  Which tube is the “experiment”?

 

 

III.  Digestion of starch:

            A.  Preparation:

 

                        1.  Pour 5 ml of 1% starch solution into a test tube labeled #5.

 

                        2.  Add 2 ml of 5% pancreatin solution to tube 5; mix well.

 

                        3.  Pour 2 ml of 1% starch solution into a test tube labeled #6.

 

                        4.  Put tubes #5 and #6 in the incubator at 40º C for about 1½ hours.

 

B.     After incubating:

1.      Put 2 ml of the mixture (mix well first!) from tube 5 into a separate, clean test tube, and add enough Benedict’s solution (about 10-20 drops) to give the tube a blue color.

                        2.  Add Benedict’s solution to tube 6 in the same manner as for the sample from tube 5.

3.      Place the sample from tube 5 and tube 6 in a hot water bath for a maximum of 5 minutes, or until color change occurs.

 

C.    What was the color change seen in the sample from tube 5?

What is the color change seen in tube 6?

 

            D.  The color change seen in the tube 5 sample indicates the presence of what carbohydrate?

 

            E.  What pancreatic enzyme is responsible for the digestion of starch?

 

F.     Why was there no color change expected for tube #6?

 

G.  Considering this demonstration of the digestion of starch:

1.  Which tube is the “control”?

2.  Which tube is the “experiment”?

 

Last Updated:  12/31/2006