Resources | Subject Notes | Biology
Enzymes are biological catalysts. They speed up chemical reactions in living organisms by lowering the activation energy. A key characteristic of enzymes is their specificity, meaning that each enzyme typically catalyzes only one specific reaction or a very limited number of closely related reactions.
The active site is a specific region on the enzyme where the substrate binds and the chemical reaction takes place. It has a unique three-dimensional shape.
The substrate is the molecule upon which an enzyme acts. The specificity of an enzyme arises from the complementary shape of the active site and the substrate. This is often described using the lock-and-key model or the induced-fit model.
The lock-and-key model proposes that the active site of an enzyme has a rigid, specific shape that perfectly fits only one particular substrate, like a key fitting into a lock. This tight fit allows the enzyme to bind to the substrate and catalyze the reaction.
The induced-fit model is a more accurate representation. It suggests that the active site is not completely rigid. When the substrate binds, the enzyme undergoes a conformational change, shifting the shape of the active site to create a more precise fit with the substrate. This conformational change optimizes the interaction between the enzyme and the substrate.
The specificity of an enzyme is determined by the arrangement of amino acids in the active site. These amino acids have various chemical properties (e.g., charged, polar, non-polar) that allow them to interact specifically with the substrate through various types of bonds (e.g., hydrogen bonds, ionic bonds, hydrophobic interactions).
| Feature | Description |
|---|---|
| Active Site | Specific region on the enzyme where the substrate binds. |
| Substrate | The molecule on which the enzyme acts. |
| Lock-and-Key Model | Enzyme active site has a rigid shape that perfectly fits one substrate. |
| Induced-Fit Model | Enzyme active site changes shape upon substrate binding to optimize fit. |
The complementary shape and fit between the active site and the substrate are crucial for the enzyme to function effectively. Only the correct substrate will be able to bind to the active site and undergo catalysis.