lactase enzyme lab report by mia bennett, KYLIE O'SHAUGNESSY and laurel wong - APRIL 6, 2017


  • lab goggles
  • hair tied back
  • used different pipettes for different solutions
  • were cautious when working with the hot solutions
  • made sure to properly dispose of all chemicals

PURPOSE: We did this lab to learn about the properties of lactase, an enzyme used in our bodies, and to understand how important they are in our body.

lactase enzyme

INTRODUCTION: Enzymes are nature's catalysts. They catalyze over 4,000 biochemical reactions and without them, we wouldn't be alive. In this experiment, we worked with the enzyme lactase. We use lactase to digest lactose, which is found in dairy products like milk and yogurt. Lactose, a native substrate, consists of two monosaccharides: glucose and galactose. Both glucose and galactose are simple sugars The reaction we studied through this experiment was the hydrolysis of lactose into glucose and galactose.

PROCEDURE: Prepare solutions

  1. Enzyme solutions: 1 lactase tablet to 200 ml water, dissolve
  2. Skim milk: contains the lactose
  3. Sucrose solution: 5 g of sure to 100 mL water, dissolve
  4. Denatured enzyme solution: 20 mL enzyme solution, 200 mL water, beaker with water into the enzyme solution then put on hot plate and boil for 30 mins. Let solution cool for 30 minutes

Lab Procedure:

  • Label test tubes
  • Make 5 different test tubes, A-E
  • test for glucose using the glucose strips in each test tube

Test Tubes:

  • A: 2 mL skim milk and 1 mL enzyme solution
  • B: 2 mL skim milk 1mL water
  • C: 2 mL skim milk and denatured enzyme solution
  • D: 2 mL sucrose solution and 1 mL enzyme solution
  • E: 2 mL sucrose solution with 1 mL water



  1. Enzyme Solution:
  • the tablet fizzed and dissolved in the water
  • bubbled and disappeared

2) Skim Milk:

  • thin, watery milk substance (once water added)

3) Sucrose Solution:

  • sugar gradually disappeared

4) Denaturing the Enzyme Solution:

  • as the water and solution heated up, the liquid began to bubble
  • bubbles formed in the water, on the outside of the tube, and the in the solution


A) Milk and Enzyme Solution

  • the glucose test strip was tinted a turquoise green
  • lactose hydrolysis reaction was present

B) Milk and Distilled Water

  • the glucose test strip remained light blue
  • no glucose produced

C) Milk and Enzyme Solution

  • the glucose test strip remained light blue
  • no glucose produced

D) Sucrose and Enzyme Solution

  • the glucose test strip remained light blue
  • no glucose produced

E) Sucrose and Distilled Water

  • the glucose test strip remained light blue
  • no glucose produced


Sucrose: C11H24O11

  • Sucrose is a pure crystalline disaccharide extracted from sugarcane or sugar beets and consisting of glucose and fructose joined together in the molecule.
  • A "disaccharide" sugar is made up of two monosaccharide sugar units
  • Monosaccharides are any sugar that cannot be hydrolyzed (broken down) to give a simpler sugar. They have carbon rings with oxygen and additional carbon, hydrogen and oxygen branches
  • In the case of sucrose the monosaccharides are glucose and fructose

Lactose: C12H22O11

  • Lactose is a type of sugar presented in milk and is the native substrate in the Lactase enzyme
  • It is composed of monosaccharides galactose and glucose
  • Lactose catalyzes the hydrolysis of disaccharide lactose into galactose and glucose. This essentially means The complete form of Lactose is indigestible to humans, and it must be hydrolyzed in able for the body to for the body to process it. Therefore, lactase is the catalyst in the process -- it reduces the amount of energy needed for the hydrolysis to occur
  • We need this reaction for digestion of lactose in dairy, it breaks down milk found in our intestine
  • For those who are lactose intolerant (The inability to fully digest sugar (lactose) and break down the lactose into its composing parts in dairy products), Lactase can be purchased in pill form
  • This lab demonstrates lactase breaking lactose down into galactose and glucose

Why does lactase only break down lactose and not sucrose?

  • Lactase only breaks down lactose (and not sucrose) because of the shape of lactose -- Lactose is able to fit in its active site where sucrose can not

What happened when the enzyme was boiled?

  • Lactase functions its best somewhere between 70-120 degrees Fahrenheit and its function is optimized around 115 degrees Fahrenheit
  • Cool temperatures slow the rate of lactase function and extremely high temperatures (greater than 135 F) can denature the lactase and cause it to lose its shape.
  • The protein's shape is responsible for its function. Therefore, when lactase becomes denatured and loses its shape, its loses its ability to function
  • If lactase is rendered nonfunctional because of temperature or pH extremes, the breakdown of lactose stops.
  • In conclusion, The heat changed the shape of the lactase and this is why the skim milk and denatured enzyme solution (heated up) did not change even when the skim milk and the regular enzyme solution worked (not denatured)

Would lowering the pH affect the enzyme?

  • Based on the optimal pH for lactase, 2-4 pH, we determined that lowering the pH of the enzyme solution would increase the efficiency of the reaction.
  • From the results we got, we concluded that there is no lactase in water, and that lactase does not have the right shape to catalyze sucrose.


In this experiment, we used glucose test strips to measure the amount of glucose present in five different mixtures. The amount of glucose present allows us to determine how much lactose has reacted. The only mixture that tested positive for glucose was the milk and enzyme solution. From this, it can be determined that this was the only mixture with both lactose and lactase (not denatured) present, and that lactase does not work as a catalyst for sucrose.

BIBLIOGRAPHY: Writer, Leaf Group. "The Effects of PH and Temperature on Enzyme Activity of Lactase on Lactose." The Effects of PH and Temperature on Enzyme Activity of Lactase on Lactose | Education - Seattle PI. Seattle PI, 22 May 2014. Web. 05 Apr. 2017. "Sucrose Dictionary Definition | Sucrose Defined." Sucrose Dictionary Definition | Sucrose Defined. N.p., n.d. Web. 05 Apr. 2017.

Lactase Enzyme. N.d. N.p.

"Figure S2: The Effect of PH on TpdE Activity." (n.d.): n. pag. Web.

Chem Rxns. N.d. N.p.

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