The Lock and Key Model Enzyme Explained!

"Just as a key fits a lock, enzymes and substrates are built for each other.”


Introduction of Enzymes

Reading about enzymes might leave you confused about how they work. The “lock and key model enzyme” has an elegant and simple explanation. Read on below to find out.


What is the Lock and Key Model?

Key definitions

In order to explain how enzymes work, we need to be aware of two important terms:

  • Enzymes: Proteins that help speed up chemical reactions. 

  • Substrates: The chemical compounds that are processed by enzymes (e.g. they can be broken down)


This shows the lock and key model enzyme of the O Level Biology concept.


Basics of the Lock and Key Model of Enzyme Action

It is one of the simplest models of enzyme action to understand. The lock and key model of enzyme action is similar to how we open a lock:

  • Only one specific key fits and opens a given lock

  • Similarly, only the correct substrate can fit a given enzyme, allowing it to work

Note how this unique pairing between enzymes and substrates maintains precision in biological processes. Specific enzymes can focus on their specific reactions and this improves efficiency in maintaining cells!


CTA Slide 1


How can a lock and key be used to describe an enzyme?

A good way to understand enzyme action is through the lock and key hypothesis:

  • The substrate can be thought of as a key (substrate = key)

  • The enzyme can be thought of as the lock (enzyme = lock)

  • When the substrate enters, it “activates” the enzyme, which starts processing the substrate

  • Other substrates will not be able to “activate” the enzyme, as their shape won’t match



In conclusion, enzymes speed up (catalyze) some key chemical reactions in organisms. The theory of lock and key enzymes says that a given enzyme only interacts with its precise substrates. 

We hope that by reading this concept guide, you developed a better understanding of the subject matter. Stay tuned to Out-Class for more study guides!

If you want to dive right in, let's start with selecting the course you want

What Course Are You Interested In?