What are active sites in enzymes?

Active sites in enzymes are specific regions where substrate molecules bind and undergo a chemical reaction.

Active sites are unique and highly specific pockets or clefts found on the surface of enzymes. They are usually formed by a group of amino acids that are not sequential but are brought together by the folding of the protein chain. These sites are the functional parts of the enzyme, where the actual catalysis occurs. The specificity of these sites is due to their unique three-dimensional structures, which are complementary to the shape of their specific substrate molecules.

The active site of an enzyme has two main roles. Firstly, it provides a site where the substrate can bind. This is often referred to as the 'lock and key' model, where the active site (the lock) is exactly the right shape for the substrate (the key) to fit into. Secondly, it provides the right conditions for the reaction to occur. This could be the correct pH, the presence of necessary ions, or the right temperature.

The active site achieves its task through several mechanisms. It may hold the substrate in a certain position to facilitate the reaction, or it may stress the bonds in the substrate, making them easier to break. It may also provide a microenvironment that is more conducive to the reaction. For example, if the reaction requires a slightly acidic environment, the active site may contain amino acids that donate protons.

In summary, the active site is a crucial part of an enzyme's structure. It is the region where the substrate binds and the chemical reaction is catalysed. The specificity of the active site ensures that enzymes can control and speed up specific reactions within the cell, making them vital for life's processes.