What is meant by the 'lock and key' model of enzyme action?

The 'lock and key' model of enzyme action refers to the specific interaction between an enzyme and its substrate.

In more detail, the 'lock and key' model is a simplified explanation of how enzymes function. It was proposed by Emil Fischer in 1894 and is based on the concept that each enzyme has a unique, fixed shape that perfectly fits the shape of a specific substrate, much like a key fits into a specific lock. The area on the enzyme where the substrate binds is called the active site.

When the substrate enters the active site, it forms an enzyme-substrate complex. This interaction triggers a chemical reaction, breaking down the substrate into its component parts or combining substrates to form a new product. Once the reaction is complete, the product is released and the enzyme is free to interact with another substrate molecule.

This model emphasises the specificity of enzymes. Just as a key can only open a specific lock, an enzyme can only catalyse a specific reaction with a specific substrate. This specificity is due to the unique shape and structure of the enzyme's active site, which is designed to interact with a particular substrate molecule.

However, it's important to note that this model is a simplification. In reality, enzymes are not rigid structures, but can change shape to better fit the substrate, a concept known as induced fit. Despite this, the 'lock and key' model remains a useful way to understand the basic principles of enzyme action.