An enzyme’s active site is a specialized region typically comprising a pocket or groove where substrates bind to the enzyme. The shape and chemical environment of the active site allow the enzyme to recognize and interact specifically with its substrates, facilitating the catalysis of biochemical reactions. The fit of the substrate into the active site is often described by the lock-and-key model, which illustrates how enzymes are selective for particular substrates and can lower the activation energy needed for reactions to occur.