Lab due in a couple of hours. I need help, Please.
Lactase Enzyme Lab
This lab will examine the specificity of an enzyme (lactase) to a specific substrate (lactose).
Students will observe the actions of the enzyme and how shape is important to enzyme reactions.
Students will also observe what will happen when the enzyme is denatured.
Materials Lactase tablets (included in lab kit) 15ml (1 tbsp. or 3 tsp) milk- any milk will do Water-used for dissolving the lactase tablet, dissolving the sucrose and boiling the
lactase Sugar-5g (1 tsp) Teaspoon Tablespoon three cups - used for dissolving the lactase tablet, dissolving the sucrose and boiling the
lactase 5 small cups/containers (must be able to heat them in microwave or place in pan of
boiling water) Clock or timer microwave or stove top glucose test strips (included in lab kit) utensil for mixing
Lactose, the sugar found in milk, is a disaccharide composed of glucose and galactose (both six
sided sugars). Sucrose, ordinary table sugar, is also a disaccharide composed of fructose and
glucose, Glucose is a six-sided sugar and fructose is a five-sided sugar.
Lactase is an enzyme that breaks lactose down into galactose and glucose. 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 because of the shape
of the sugar.
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. Solution preparation
1. Enzyme solution: Add one lactase tablet to two hundred milliliters (6.5 oz) of water. Stir
until the tablet has dissolved.
2. Skim milk: this solution contains the lactose
3. Sucrose solution: Add 5 grams (1 tsp) of sugar to 100ml (3.5 oz) of water. Stir until the
sugar has dissolved.
4. Prepare a denatured enzyme solution
a. Place twenty milliliters (1.5 tbsp) of enzyme solution that you prepared above into
a small container (one that can be heated either on the stove top or in the
microwave. ex small glass or metal measuring cup.)
b. Add two hundred ml (6-7 oz) of water to a container that can be placed on the
stove top or in the microwave (the water must be high enough to come up over the
smaller container that you are heating. You are creating a hot water bath.)
c. Place the small container in the beaker or larger container. Place the larger
container and test tube or smaller container on the stove top or in the microwave.
d. Boil the water in the beaker for 30 minutes
e. Let the solution cool to room temperature
1. Gather the materials
2. Label the small containers/cups with the following labels: A B C D E
3. To container A add 2ml of skim milk and 1ml of enzyme solution
4. Time for 2 minutes and test for glucose with the glucose test tape. Record this data in
table 1. If these was glucose present mark a ?+? in the table. IF glucose was absent, mark
a ?-? in the table.
5. To container B add 2 ml of skim milk and 1ml of water.
6. repeat step 4
7. To Container C add 2ml of skim milk and 1ml of denatured enzyme solution
8. repeat step 4
9. To container D add 2ml of the sucrose solution and 1ml of enzyme solution
10. repeat step 4
11. To container E add 2 ml of the sucrose solution and 1 ml of water
12. repeat step 4 Name _________________________________________ Date _____________ Lactase Enzyme Lab
Glucose Test Results
Type of Solution
Test Tube A: milk and enzyme solution
Test Tube B: milk and water
Test Tube C: milk and denatured enzyme solution
Test Tube D: sucrose solution and enzyme solution
Test Tube E: Sucrose solution and water Glucose Test (+ or -) Conclusion and questions
1. Diagram and describe the lactose and lactase reaction 2. Why did the enzyme react to lactose but not to sucrose? 3. What happened when the enzyme was boiled? 4. 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? 5. What type of reaction is this? Dehydration or hydrolysis? Enyzmes
For each question, click the circle next to the correct answer.
1. Without the presence of enzymes, the reactions necessary to sustain life would
require ___________________ in order to occur.
smaller atoms 2. Based on the graph, which of the following could be used to increase the reaction
rate beyond point C?
increase the amount of substrate
add more water
increase the temperature
decrease enzyme concentration
3. The part of the enzyme where the substrate binds is called the:
large subunit 4. When a piece of liver is dropped into hydrogen peroxide, the peroxide bubbles
vigorously as a result of what reaction?
peroxide being broken into water and oxygen
peroxide is destroying germs in the liver
more peroxide is being created by the liver
liver and peroxide are joining together to make a new protein
5. Some people cannot digest milk products because they lack a specific enzyme.
Which enzyme would be used to break down the lactose in milk?
lactase 6. On the image, which letter represents the enzyme?
7. On the image, which letter represents the substrate?
8. On the image, which letter represents the product of the reaction?
D 9. In what way could you increase the rate of the reaction as it taking place in image C.
add more substrate
add more enzyme
10. Enzymes are composed of what organic molecule?
proteins Lactase Enzyme Lab
Teachers Answer Sheet Teachers will be able to assess the results table (the only positive reaction should be test tube A)
and the teacher will be able to correct the conclusion questions.
1. the students should draw a hydrolysis-induced fit model
2. The shape of sucrose (glucose and fructose) is different from lactose (glucose and
galactose). The sucrose will not fit into the active site of lactose.
3. The enzyme denatured. The hydrogen atoms vibrated so much due to the energy added to
quaternary structure of the enzyme. Note: as long as the students understand that the
bonds broke changing the enzyme shape, they are ok.
4. The enzyme will denature (eventually). The H+ will interfere with the hydrogen bonds,
and denature the enzyme.
5. The reaction is a hydrolysis reaction.
Denaturing the enzyme was very difficult. We had to boil the enzyme (placing a test tube with
the enzyme in a beaker of boiling water) for 30 minutes.
We thought about lowering the pH of the enzyme solution, but commercial lactase is swallowed
and works in the stomach, so lowering the pH was not really an option for us.
We experimented by boiling the lactase for five, ten and fifteen minutes. Thirty minutes worked
for us. We suggest that you try boiling the enzyme before the lab, adding some milk (source of
lactose) and test for glucose. If glucose is present, boil the lactase for a longer period of time.
You can approach the enzyme specificity in two different ways:
1. Why didn?t the sucrose break down in the presence of lactase?
2. Why didn?t the lactose break own in the presence of boiled lactose?
This lab is an uncomplicated introduction to enzyme reactions.
This lab is a relatively simple lab which shows the specificity of enzymes based on shape. You
will need to purchase lactaid and glucose test strips. I suggest the glucose test strips from Science
Kits and Boreal Labs, which are easy to use.
You might want to set up the solutions before the lab (if you are pressed for time). This will
simplify the lab for the students.
This question was answered on: Sep 18, 2020
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