Name _____________________________________________
Date _______________________
Lactase Enzyme Lab
Introduction:
Lactose, the sugar found in milk, is a disaccharide composed of the monosaccharides, glucose and galactose
Sucrose, ordinary table sugar, is also a disaccharide composed of glucose and fructose.
Enzymes act as organic catalysts to regulate the rates of reactions to maintain normal homeostasis within the
body of living organisms. They have a specific molecular structure which binds to a specific structure of the
substrate, or molecule that they act upon. The enzyme and substrate will bind together at an area on the
enzyme known as the active site. It is like the teeth on a key fitting into a specific lock. If they don’t have
complementary shapes, they cannot bind. This is called the Lock and Key theory.
Enzyme
EnzymeSubstrate
complex
Enzyme
https://biochem80p.files.wordpress.com/2014/03/enzyme-working-mechanism.jpg
Lactase is an enzyme that breaks lactose down into glucose and galactose. Lactase can be purchased in pill
form by people who are lactose intolerant. These people lack the enzyme, lactase, and cannot break down the
sugar lactose into its component parts. Although lactose is similar to sucrose, lactase will break down only
lactose- due to the shape of the sugar.
In this lab, you will see lactase break lactose down (in skim milk) into galactose and glucose. You will also
observe what happens if the shape of lactase is changed due to heating. This process is called denaturing. The
shape of the active site gets altered much like melting the teeth on a key. It won’t work in the lock anymore.
Denaturing of enzymes in our bodies is very difficult due to our body’s attempt to maintain homeostasis. In this
lab, we had to boil the enzyme (placing a test tube with the enzyme in a beaker of boiling water) for thirty
minutes.
Purpose: This lab will examine how enzymes are specific to a substrate. You will also observe what happens
when the enzyme is denatured by heat and thus, changing its active site.
Materials:
Enzyme (Lactase) solution
Skim Milk
Water
Sucrose solution
10 ml Graduated cylinder
5 Test Tubes
Test Tube Rack
Marking Pencil
Labeling tape
Glucose Test Strips.
Stirring Rod
Procedures:
1) Put on your goggles and gather your equipment
2) Label the 5 test tubes with the following labels:
A. Skim milk + enzyme
B. Skim milk + water.
C. Skim milk + denatured enzyme
D. Sucrose + enzyme
E. Sucrose + water.
3) In test tube A, add 2 ml of skim milk and 1 ml of enzyme solution.
4) In test tube B, add 2 ml of skim milk and 1 ml of water.
5) In test tube C, add 2 ml of skim milk and 1 ml of denatured enzyme solution.
6) In test tube D, add 2 ml of the sucrose solution and 1 ml of enzyme solution.
7) In test tube E, add 2 ml of the sucrose solution and 1 ml of water.
8) Now wait 2 minutes after you have filled all the test tubes then test each test tube solution for glucose with
the glucose test tape. Glucose test strips are normally a teal color. They will change from teal to green or brown
with a higher concentration of glucose. Any change from this teal is a positive result. If there was glucose
present, mark a '+' in the table. If glucose was absent, mark a '-' in the table. Record this data in table 1.
Table 1: Glucose presence in solutions
Glucose test
Treatment
Strip results
Test Tube
( + or -)
Skim milk +
1
Enzyme
4
Skim milk +
water
Skim milk +
Boiled enzyme
Sucrose +
Enzyme
5
Sucrose + water
2
3
Conclusion/Questions:
1.
What is an enzyme?
2.
What part of the enzyme will bind to the substrate (the molecule it acts upon)?
3.
What happened in the lactose and lactase reaction to produce a positive glucose test strip result?
4.
Why did the enzyme lactase react to lactose and not to sucrose?
5.
What happened to the enzyme when it was boiled?
6.
Another way to affect the enzyme is by lowering the pH of the solution. However, lactase is supposed
to be able to work in the stomach. Would lowering the pH of the enzyme solution affect the
enzyme? Why or why not?
7.
What type of reaction is this? Dehydration synthesis or Hydrolysis? Explain your answer.