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Enzyme-Controlled Reactions
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To sustain the processes of life, a typical cell carries out thousands of biochemical reactions each second.
Many of these reactions require the help of enzymes. Enzymes are proteins that speed up the rate of
chemical reactions. Many important processes in the body involve the work of enzymes, including the
digestion of nutrients such as carbohydrates, proteins and fats.
Enzymes are organic catalysts. A catalyst is a chemical that controls the rate of a reaction, but is itself not
used up in the process. Reactions that are accelerated due to the presence of enzymes are known as enzymecatalyzed reactions.
Enzymes are proteins that accelerate chemical reactions but do not change themselves in the reaction.
Enzymes enable molecules to undergo chemical changes, forming new substances called products.
Substrates are molecules that are acted upon by enzymes. For instance, amylase, an enzyme found in saliva,
helps break down complex starch molecules (substrates) into smaller sugar molecules (products). In other
biochemical reactions, substrates require assistance of specific enzymes to form new products.
Each substrate fits into an area of the enzyme called the active site. This fitting together is often compared to
a lock-and-key mechanism. However, researchers believe that the fit between enzyme and substrate need
not be exact. Enzymes are viewed as flexible keys that can shape and conform to the shape of the substrate.
Real–life example: Lactose intolerance____________________________________________________
Millions of people suffer from an enzyme related condition called lactose intolerance. Lactose is a
disaccharide that is commonly referred to as dairy sugar. In normal individuals who eat lactose, their
digestive system produces the enzyme lactase which breaks down the sugar lactose into two
monosaccharides- glucose and galactose which can be used by the body. In a person with a lactose
intolerance, there in not enough of the lactase enzyme produced to break down the substrate lactose. When
this individual eats lactose, it cannot be broken down sufficiently in their digestive tract. This leads to the
discomfort associated with lactose intolerance such as cramps, bloating, gas and diarrhea.
Problem: How do lactose concentration and pH affect the rate of a lactase-catalyzed reaction?
Background Information: Answers can be found in the reading from above
(Restate the question in your answer)
1.
2.
3.
4.
5.
6.
What is an enzyme? Give an example.
What is a catalyst? Give an example.
Do enzymes change after a chemical reaction has occurred?
What is a Substrate? Give an example.
How can an individual have different pH values in their body? (Think back to your notes on this)
How do you think pH value will affect the effectiveness of an enzyme?
Hypothesis: Write your own hypothesis based on your knowledge of acids and bases. What pH value does
the body need to efficiently break down lactose? (Write it as a “If…then” statement)
Procedure:
1. Search Google for pH and enzyme virtual lab and find this very specific website:
http://www.mhhe.com/biosci/genbio/virtual_labs_2K8/labs/BL_02/index.html
2. Change the pH value of each test tube to correlate with the numbers below: (TT =test tube)
TT1= 3
TT2=5
TT3=7
TT4=9
TT5=11
3. Add 0.5 g of lactose to each test tube 1-5.
4. Click on the computer monitor to get your results.
5. Repeat Step 3 and 4 changing the amount of lactose each time until you reach 8.0 g of lactose.
6. Record your results in the Observation chart on your Lab Report.
7. Graph your results with Number of Glactose and Glucose Molecules Formed per Minute vs. Lactose
in grams on your Lab Report.
8. Use a different color for each Test Tube. (Ex. Yellow = TT1, Green = TT2 …)
Conclusion: 5-6 sentences
-Summarize the procedure you followed for each test tube.
-Was your prediction correct?
-What were your results for each test tube? Look at the data from your table and write it in to sentence
form.
-DON’T write every single number. Summarize what happened in each test tube.
(Example: “Test tube 1 had a pH value of 3 and it started at ______ molecules with 1.0 grams and
leveled off at ______ with 8.0 grams”)
Analysis: See Lab Report
Enzyme-Controlled Reactions
Name ________________________
Problem:
Period ________
Background Information:
Observations:
Grams of Lactose
0.5
1.0
2.0
4.0
8.0
Graph:
Key
Color
Test Tube 1
pH=
Test Tube 2
pH=
Test Tube 3
pH=
Test Tube 4
pH=
Test Tube 5
pH=
Test Tube 1
pH=3
Test Tube 2
pH =5
Test Tube 3
pH=7
Test Tube 4
pH=9
Test Tube 5
pH=11
Conclusion: 5-6 sentences
Summarize the procedure you followed for each test tube. Was your prediction correct? What were your results for each test tube?
Look at the data from your table and write it in to sentence form. DON’T write every single number. Summarize what happened in
each test tube. (Example: “Test tube 1 had a pH value of 3 and it started at ______ molecules with 1.0 grams and leveled off at
______ with 8.0 grams”)
Analysis:
1. Describe the relationship between substrate concentration and initial reaction rate of an enzyme-catalyzed reaction.
What happens to the initial reaction rate as substrate concentration increases?
2. What is the maximum initial reaction rate for the lactase enzyme at pH 7?
3. Explain why the maximum initial reaction rate cannot be reached at low lactose concentrations.
4. What does your data indicate about the optimum pH level for this Lactase-catalyzed reaction?
5. People with a lactose intolerance are able to take products such as Lactaid that contain the lactase enzyme with
their meals. These products can be taken in pill form. Considering the fact that the pill form of the enzyme would have
to travel through the person’s stomach, what special consideration would the producer of this product need to be
concerned about?