Category: Resources

INTRODUCTION:

In this experiment you will observe the action of the enzyme amylase on starch. Amylase changes starch into a simpler form: the sugar maltose, which is soluble in water. Amylase is present in our saliva, and begins to act on the starch in our food while still in the mouth.
Exposure to heat or extreme pH (acid or base) will denature proteins. Enzymes, including amylase, are proteins. If denatured, an enzyme can no longer act as a catalyst for the reaction.
Benedict’s solution is a test reagent that reacts positively with simple reducing sugars like maltose, but will not react with starch. A positive test is observed as the formation of a brownish-red cuprous oxide precipitate. A weaker positive test will be yellow to orange.

MATERIALS:

Cornstarch Distilled water Saliva Vinegar Benedict’s qualitative solution 3 graduated cylinders (10mL) 250-ml beaker Stirring rod 3 test tubes (16 x 125mm) Test tube rack Wax pencil Water Bath

PRE-LAB:

Add 1g of cornstarch to a beaker containing 100ml of cold distilled water. While stirring frequently, heat the mixture just until it begins to boil. Allow to cool.

PROCEDURE:

1. Fill the 250-mL beaker about 3/4 full of water and place on the hot plate for a boiling water bath. Keep the water JUST AT BOILING.

2. Mark 3 test tubes A, B and C. “Spit” between 1 and 2 mL of saliva into each test tube.

3. Into tube A, add 2 mL of vinegar. Into tubes B and C, add 2 mL of distilled water. Thump the tubes to mix.

4. Place tube B into the boiling water bath for 5 minutes. After the five minutes, remove from the bath, and place back into the test tube rack.

5. Add 5 mL of the starch solution to each tube and thump to mix. Allow the tubes to sit for 10 minutes, occasionally thumping the tubes to mix.

6. Add 5 mL of Benedict’s solution to each tube and thump to mix. Place the tubes in the hot water bath. The reaction takes several minutes to begin.

OBSERVATIONS:

Tube A: Starch + saliva treated with vinegar (acid)

• Was the test positive or negative? _______________________

What does this indicate?__________________________________________________

____________________________________________________________________

____________________________________________________________________

Tube B: Starch + saliva and water, treated in a boiling water bath

• Was the test positive or negative? _______________________

What does this indicate?__________________________________________________

____________________________________________________________________

____________________________________________________________________

Tube C: Starch + saliva

• Was the test positive or negative? _______________________

What does this indicate?__________________________________________________

____________________________________________________________________

____________________________________________________________________

QUESTIONS:

1. What is the function of an enzyme?

2. Where does a substrate attach to an enzyme?

3. If an enzyme is present in a reaction, less ________________ _________________ will be needed to get the reaction started.

4. What is a common suffix found at the end of most biological enzymes?

5. Most enzymes are macromolecules called ________________.

6. Define denaturation of proteins.

7. Name 3 things that can denature or unfold an enzyme.

8. In this lab, what weak acid denatured the protein?

9. What was the purpose of placing one test tube in a hot water bath?

10. What happens to enzymes in your body whenever you run fever?