Lock and Key Analogy with Enzymes

Written by Michelle Zurawski, Moraine Valley Community College

This is an analogy that is used during the enzyme discussion. I compare the enzyme substrate complex with a lock and key. My car is a cheap fuel efficient little car so I tell the students that I would like upgrade to a nicer Prius. I ask them if I could go to the parking lot and open a nice new Prius with my key. I then tell them that this is one of the ways that enzymes work to save energy. You only need a small amount of enzyme (1 key) to work with a specific substrate (1 car). Just think if you had to make a new key every time you opened up your car door. That saves energy by using that same enzyme (car key) over and over for the same reaction (car). Enzymes are specific to one substrate just like the key to my car is specific to my car. You can also use the two puzzle pieces fitting together like an enzyme and a substrate only fitting together in one way.

The Energy Barrier for a Chocolate-Craving Pregnant Woman

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

When discussing the energy of activation (EA) related to enzymes, I tell students about when I was pregnant and ate ice cream every night. I explain that after dinner I would sink into my deep, fluffy sofa. When I deemed it ice cream time, it was challenging to get up to get from the sofa with a big belly. I would complain and huff and puff,  etc. But sometimes, my lovely husband would hold his arm out and help to pull me off the sofa. In this analogy, my husband is the enzyme (catalyst) because he lowered the energy barrier for me. However, he didn’t make the impossible happen—I would have gotten that ice cream on my own—he just made it easier and faster for me to be a happy pregnant woman full of ice cream (the product of the reaction).

Students, Design Your Own Enzyme-Catalyzed Reaction

Written by Kelly A. Hogan, University of North Carolina at Chapel Hill

Learning Outcomes:

– To practice using terms related to enzyme-catalyzed reactions

– To address a misconception that enzymes are depleted after a reaction

Activity Description: Students are given a list of words and instructions to design their own enzyme-mediated reaction. Students work in small groups to design and then demonstrate their idea to the class (students can use simple props). The whole class can decide if the demonstration is designed well to illustrate understanding. The activity can work in a small class or a large class in which only a few groups get to demonstrate. You may also choose to simply demonstrate your own example asking students to come up with ideas as you prompt them.

Time Needed: Activity may take 40 minutes (if students do group work outside of class) and may take much longer if group time is given during class

Materials Needed: Variable depending on students

Activity Instructions:

Tell students that they will design an enzyme-catalyzed reaction (could be dehydration synthesis, hydrolysis, functional group transfer, etc.) that shows their understanding of the words/ideas below. The materials students have available can be props available in a classroom, such as classmates, paper, pens, etc. You may suggest that students work outside of the class and plan ahead to bring simple props with them. Groups will demonstrate their ideas to the class. You may want to have a panel of student judges (American Idol style).

Ideas that students can demonstrate:

A. active site

B. substrate

C. product

D. enzymes are used over and over.

E. enzymes can be inhibited at their active site or their allosteric site.

F. enzyme activity is affected by environmental conditions.

Example: I place a bowl of wrapped candies on my table. I tell them that I am unwrappase. The substrate is wrapped candy and the product is unwrapped candy. My hands are the active site. A single me can unwrap many candies (enzymes are used over and over and are unchanged). The rate of me producing unwrapped candies would slow down if pistachio nuts were mixed into my bowl because the pistachio nuts would temporarily bind to my active site. Pistachios would be competitive inhibitors. If a scarf was tied around my elbows to connect them behind my back, the active site would be altered because my hands would open up and I would have trouble holding the candy. The scarf would be an allosteric inhibitor. Ideally, I work best at room temperature. If the heat was turned way up or way down my activity might be slowed by these environmental conditions, and I might be cranky and produce less product.