GCSE Biology – Lock and Key Theory of Enzymes

Lock-and-Key Theory of Enzyme Action

Enzymes are biological catalysts that speed up reactions in the body. A substrate is the molecule an enzyme acts on, and it binds to a particular region of the enzyme called the active site.

In the lock-and-key model, the active site and its matching substrate have complementary shapes: the enzyme is like a lock, and the substrate is like a key. Enzymes are specific, so a substrate with the wrong shape will not fit or bind to the active site.

When the correct substrate binds, an enzyme–substrate complex forms. The enzyme then helps convert the substrate into products. Enzymes can catalyse reactions that break a substrate into smaller products or join smaller substrate molecules to make a larger product.

The video includes pause-and-answer questions to help learners check their understanding and practise using key terms.

Speakers and Sources

• Narrator/presenter: Unidentified educational voice
• Source named in the subtitles: kscience.com