Locked out...again?-Enzymes, part 2

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Students will explore the lock and key model to better understand how enzymes work.

Big Idea

If the enzyme doesn't fit, the reaction will quit.


5 minutes

Warm-Up: Look at the picture to explain what enzymes do and how do they do it.

Ask this question as quick formative assessment to determine if students met the learning targets from the previous lesson on enzymes.  Listen for any misconceptions about what enzymes do and how they work. 

Look for students to more easily identify that enzymes speed up chemical reactions.  Expect less accuracy of explanation about how they are able to speed up reactions.  Use the visual image to help show that enzymes lower the activation energy needed to start a reaction.  Help them visualize a hill with a less steep slope by drawing a lower line on the page.  Ask them if they would be able to move a boulder over the higher hill or the lower hill faster and why.  Ask questions of several students to ensure that all students possess an understanding that enzymes lower the activation energy needed to start a reaction.

Review of Content

15 minutes

Use a LCD projector to show an enzyme animation.  Use the buttons on the movie to display each segment of the animation.   Ask for a volunteer reader to read aloud each of the pages that precede the animation segments:

  • Some enzymes break down substances
  • Some enzymes build raw materials into complex molecules
  • Enzymes are specific
  • Denaturing
  • Enzyme inhibition

After each segment, ask questions to assess students’ understanding of what they have seen. For example, ask “How did the enzyme help?” after watching the reaction without the enzyme and the reaction with an enzyme.  Re-play the animation segments as many times as needed to help students understand and be able to explain what they have seen.


Concept Reinforcement

15 minutes

Inform students that they will now engage in an activity that will allow them to visualize the concepts of “specificity” and the “lock and key” model.  Inform them that the learning objective for today is that they will be able to explain how the “lock and key” model relates to how enzymes work.

Distribute 1 locks and a set of 4 keys to small groups of 2-4 students.    Inform them that they will use these materials to complete the task.  One lock  per group is adequate to model the lock and key concept.  Make sure that only one of the keys given to each group will open the lock.  This models specificity in a clear way that students will understand and remember.   It's a good idea to keep the keys and lock in small bags to help with organization and minimize confusion.

Provide both verbal and written instructions for the task using a LCD projector for the different learner types.  Begin by instructing students to write one of two sentences about how a lock and key work. Then, instruct students to make three observations about the lock and keys that they received.  Afterwards, instruct students to try the keys and the lock using each of the keys they received.  Display the 5 questions they will need to answer after they find the correct key for the lock.  

Remind students that all responses to the questions should be written in complete sentences.  Walk around to monitor that all students are on task and able to cite facts that help them answer the questions. Listen for students’ ability to correctly identify their rationale for their answers.

If time permits, instruct students to trace the outline of the keys before putting trying them in the lock.  Ask students to make a prediction about which key will work.  Also, ask students to draw what the “substrate” must look like based on the shape of the key that unlocks the lock.


Independent Practice

10 minutes

Instruct students to compare and contrast  enzymes/substrates to locks/keys.  Expect students to be able to make 2-3 comparisons.  Look for significant similarities like both can be used over and over again or that both can be altered so that the key no longer fits. A key difference to look for is that enzymes are made of proteins and keys are not. One of the student work samples  shows a clear understanding of these points.  The other shows that the students could identify key properties of enzymes but the student struggled to contrast enzyme properties with locks and keys. 

Review the student work responses to determine areas where more teaching is needed based on the strengths or weaknesses of the compare/contrast responses.  For example, the other student work sample that is included indicates that the student understands the structure of enzymes.  

But, the lack of accurate responses for how locks differ from enzymes and the statement that enzymes are living indicates that the student does not possess full understanding of their functionality.   This type of response indicates that reinforcement of concepts is needed about the function of enzymes.

Lesson Close

5 minutes

Close the lesson with a different video animation that recaps how enzymes work.   Follow the playing of the animation with the 5 questions that accompany the animation.  Work through each of the responses as a class, allowing students to respond to each of the questions.  Make sure that you select both students who are raising their hand and also those who are not.  

If time permits, re-play the video clip when a student selects the wrong answer.  Do not give the correct answer.   Allow students to watch the clip in order to self-correct their thinking to arrive at which response is correct.