Enzymes are biological molecules that act as catalysts to accelerate chemical reactions. They work by lowering the activation energy required for a reaction to proceed. Enzymes are highly specific to their substrates, often catalyzing only one particular reaction. This specificity is due to the unique three-dimensional structure of the enzyme's active site, which binds to the substrate. Enzymatic bioconversions often occur under mild conditions, such as ambient temperature and neutral pH, making the process energy-efficient and cost-effective.