Lab: GOT MILK?ENZYME ACTIVITY AND LACTOSE INTOLERANCE

Purpose: In this lab, you will see lactase break lactose down into galactose and glucose. You will also observe what happens if the shape of lactase is changed due to heating.

BACKGROUND: Lactose is milk sugar. It is composed of two molecules of "simple" sugars chemically bonded together - glucose and galactose.Sucrose (ordinary table sugar) is a disaccharide composed of fructose and glucose. Glucose is a six-carbon sugar and fructose is a five-carbon sugar.Although lactose is similar to sucrose, common table sugar, lactase will break down only lactose because of the shape of the sugar. The shape of the enzyme can be altered by a low pH, or high temperatures, which denature the enzyme, inhibiting it from breaking down the substrate.

The enzyme lactase breaks down lactose into glucose and galactose, which are easily digested by humans. Most human infants produce enough lactase for milk digestion. However, in the vast majority of adult humans, the gene which specifies production of lactase is turned "off" and these individuals cannot digest lactose - they are lactose intolerant; these people lack the lactase enzyme, and cannot break down the sugar lactose into its component parts. These individuals will often purchase Lactaid®, a brand of milk that has lactase added to it so that the lactose is already broken down.

Since lactose is a sugar, it is an ideal food for the bacteria which normally inhabit our intestine (and are essential to digestion).The lactose will be digested by these same friendly bacteria, and they will produce lots of GAS!!! So most folks who are lactose intolerant choose to avoid lactose-containing milk products associated with the intolerance syndrome. Lactase can be purchased in pill form by people who are lactose intolerant for that occasional ice cream treat!

MATERIALS

Regular Milk

Sucrose Solution

Glucose Solution

Enzyme Solution

Denatured Enzyme Solution

Stomach Acid Solution (HCl)

Culture Tubes(8 Per group )

Diastix Test Strips: (8 Per Group)

Water

250 ml Beaker

Paper Towels

PROCEDURE

  1. Gather the materials.
  2. Test that your glucose test strips work by testing them with positive and negative controls.

a)Tube #1: positive control: glucose solution

b)Tube #2 negative control: water

c)Record any color changes of the strip and compare to the key on the Diastix bottle.

  1. Label the test tubes with the following labels:

a)Milk and enzyme

b)Milk and water.

c)Milk and denatured enzyme (Heat)

d)Milk and denatured enzyme (Acid)

e)Sucrose solution and enzyme

f)Sucrose solution and water.

  1. In test tube A add two milliliters of milk and one milliliter of enzyme solution.

a)Test immediately, record results

b)Test again after 2 minutes, record results

  1. In test tube B add two milliliters of milk and one milliliter of water.
  2. In test tube C add two milliliters of milk and one milliliter of denatured enzyme solution (heat).
  3. In test tube D add two milliliters of milk and one milliliter of denatured enzyme solution (acid).
  4. In test tube E add two milliliters of the sucrose solution and one milliliter of enzyme solution.
  5. In test tube F add two milliliters of the sucrose solution and one milliliter of water.
  6. Time each mixture of solutions for two minutes, then test for glucose with the glucose test strip. The test strip only needs to be dipped into the solution. It doesn’t need to soak.
  7. Record your results in table 1.

a)If there was glucose present mark a ‘+’ in the table.

b)If glucose was absent, mark a ‘-’ in the table.

NAME ______PER______

Lab: GOT MILK?ENZYME ACTIVITY AND LACTOSE INTOLERANCE(25 points)

PRE-LAB QUESTIONS:

  1. What is Lactose?
  2. What is Lactase?
  3. What are the symptoms of lactose intolerance?
  4. What is the difference between Lactose and Sucrose? (Hint: you may need to research this)
  5. Is unbound glucose present in milk? What about in Lactaid®? Why?

DATA:

TABLE 1:

TUBE / Tube #1 / Tube #2 / Tube A / Tube B / Tube C / Tube D / Tube E / Tube F
Contents / glucose / water / milk and enzyme / milk and water / milk and
denatured enzyme
(Heat) / milk and
denatured enzyme
(Acid) / sucrose and enzyme / sucrose
and water
+/-
Color

Analysis:

  1. What was the purpose of tube #1 and tune #2?
  1. What are the reactants and what are the products in the above reaction?
  1. Tube A tested negative for glucose at first and the changed to positive after 3 minutes. Explain why this happened.
  1. Diagram and describe the lactose and lactase reaction.
  1. Why did the enzyme react to lactose but not to sucrose?
  1. What happened when the enzyme was heated (boiled)?
  1. What happened when we added “Stomach Acid” to the enzyme that was placed in Tube D?
  1. 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. Should lowering the pH of the enzyme solution affect the enzyme? Why or why not?