Enzyme active sites are specific regions on an enzyme where substrate molecules bind. These sites are typically shaped to fit particular substrates, allowing the enzyme to catalyze biochemical reactions efficiently. The unique structure of the active site is crucial for the enzyme's function, as it determines which substrates can interact with the enzyme. When a substrate binds to the active site, it forms an enzyme-substrate complex. This interaction lowers the activation energy required for the reaction, enabling the conversion of substrates into products. The specificity of the active site ensures that enzymes, such as amylase or lipase, only catalyze specific reactions, maintaining the efficiency of metabolic processes.