Enzymes and Substrate Concentration Lab

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Objective

Students will determine the effects of substrate concentration and pH on the rate of a catalyzed reaction.

Big Idea

Substrate concentration matters.

Warm-Up

5 minutes

Warm-Up: Which of the following factors affect enzyme activity?

               A. temperature and pH only

               B. amount of enzyme and substrate only

               C. temperature and amount of enzyme only

               D. temperature, pH, and amount of both enzyme and substrate

This question serves as a preview of the lab.  Engage students in academic discourse.  Make sure that students understand the correct answer and why it is the best answer.

Content Review

5 minutes

Quickly assess student’s prior knowledge by asking students if they know what enzymes are or how they are used.  Provide a review of key terms: enzyme, substrate, active site, pH, substrate concentration to ensure that students have adequate preliminary knowledge to complete the lab. Use a visual image to support students' recall of concepts related to enzyme function. Look for students to explain why the blue line represents the uncatalyzed reaction.   Students should be able to identify that  enzymes speed up chemical reactions by lowering activation energy.  Also, listen to make sure sure that students know that catalyst is another name for enzyme.  

Use a second image to support assessment of students' understanding of the lock and key model.  Ask questions to determine if students understand the relationship between the substrate and active site. Ask why the term, lock and key is appropriate for describing the enzyme-substrate complex.

Guided Practice

15 minutes

Explain that students will use an online lab simulation  found on the Glencoe website to determine the effects of substrate concentration and pH on catalyzed reactions. 

Distribute computers and copies of the online enzyme lab simulation.  Display a copy of the lab using a LCD projector.  Read the lab purpose aloud to the class.

Read the 2 questions that the lab seeks to answer:

  • How does substrate concentration affect enzyme controlled reactions?
  • How does pH affect enzyme controlled reactions?

Allow students to develop a hypothesis for each question.

Review behavioral expectations for computer use. Inform students that this lab assignment is a timed activity that should not require more than 35-40 minutes to complete.

Present an overview of the lab simulation on enzymes, explaining the activities that students will perform on the computers.

Using the LCD projector, perform 1-2 steps of the procedure so that students will know how to use the simulation functions.  Be sure to model use of the journal, calculator, table and journal functions.

Emphasize the need for students to carefully read and follow the lab instructions.  Make sure that struggling readers are provided headsets so that they can listen to the audio instructions as they work to complete this multi-step procedure.

Display the data/analysis sheet.  Explain each part of the data tables, making sure that students note that data Table 1 is for substrate concentration and data Table 2 is for pH level.

Discuss how the data should be displayed after it is collected and recorded.  Provide graph paper for students to use.  Review independent and dependent variables.

Expect that students will point out that they have already performed a pH lab but remind them that reinforcement of the relationship between pH and enzyme function is beneficial to all students.

Independent Practice

20 minutes

Instruct students to take 5-7 minutes to perform a close read of the lab.  Instruct students to write down any questions that they have as they read the lab.  The close read strategy allows students to read with a purpose; which is to learn what the lab will require them to do and know. At the end of the allotted time, give students an opportunity to ask their questions so that you can provide clarification and eliminate confusion about the procedure.

Ask 1-2 students to summarize the lab procedure as a check for understanding.  

Walk around while students are working.  Watch students as they work to ensure that they are able to adjust the substrate and pH levels correctly by clicking the arrows below each test tube.  Listen to students' comments and address errors in thinking or provide support, as needed.  Look for actions that reflect correct procedures according to the lab instructions and appropriate use of time on the computers.

Student 1 and student 2 both indicate that students were able to follow complex instructions to test their hypotheses that substrate concentration and/or pH level affect enzyme function.  The work also evidence that students were able to correctly transfer the data to a graph.

 

Close

5 minutes

Ask, “Do enzymes function only at a specific pH or within a range of pH values? How do you know?" Instruct students to evaluate the graphs they created to answer this question.

Look for students to show understanding of how to interpret a graph by noting that the line increased to a point before it started to fall.

Engage students in discussion for the remaining minutes of class.  Listen to their comments and affirm that the graphs show that the enzymes work within a range up to an optimal pH before denaturation occurs.  

Ask, "How does the graph show that denaturation has occurred?" Students should be able to identify that the drastic drop of the line indicate that the enzyme no longer functions.