Enzymes

5.1 Enzyme Action: Active Site Shape and Substrate/Product Formation

Enzymes are biological catalysts. This means they speed up chemical reactions in living organisms without being consumed in the process. Their remarkable efficiency is due to their specific three-dimensional structure, particularly the active site.

The Active Site

The active site is a specific region on an enzyme molecule where the substrate binds and the chemical reaction occurs. The shape of the active site is highly specific and complementary to the shape of its substrate. This is often described using the lock-and-key model or the induced-fit model.

Lock-and-Key Model

The lock-and-key model suggests that the active site of an enzyme has a rigid, specific shape that perfectly fits only one particular substrate, much like a key fits only a specific lock. This precise fit ensures that only the correct substrate can bind to the enzyme.

Induced-Fit Model

The induced-fit model is a more accurate representation. It proposes that the active site is not a rigid structure but can change shape slightly when the substrate binds. This conformational change helps to create a more precise fit between the enzyme and the substrate, optimizing the interaction and facilitating the reaction.

Substrate Binding and Product Formation

When the substrate binds to the active site, it forms an enzyme-substrate complex. This complex is held together by weak bonds, such as hydrogen bonds and ionic bonds. The enzyme-substrate complex then undergoes a chemical reaction, converting the substrate(s) into product(s). The product(s) are then released from the active site, and the enzyme is free to catalyze another reaction.

Diagram of Enzyme Action

Table: Key Concepts in Enzyme Action

Concept	Description
Active Site	The specific region on an enzyme where the substrate binds.
Substrate	The molecule that the enzyme acts upon.
Enzyme-Substrate Complex	The temporary complex formed when the substrate binds to the active site.
Product	The molecule(s) formed as a result of the enzyme-catalyzed reaction.
Specificity	The ability of an enzyme to bind to only one specific substrate.

The specific shape of the active site is crucial for enzyme specificity. Even small changes in the shape of the active site can prevent the substrate from binding effectively, reducing or eliminating the enzyme's activity.