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).