Final answer:
A substrate is the specific reactant that an enzyme acts upon in a biochemical reaction, binding to the enzyme's active site to form an enzyme-substrate complex. The enzyme facilitates the reaction and remains unchanged afterward, able to catalyze subsequent reactions.
Step-by-step explanation:
A substrate is a molecule that an enzyme acts upon during a biochemical reaction. It is specifically the reactant that is catalyzed by an enzyme. During the reaction, the substrate binds to a particular part of the enzyme called the active site. This is often visualized as the key (substrate) fitting into a lock (enzyme's active site). After binding, the enzyme helps convert the substrate into another molecule called the product. The structure of the active site is highly specific, allowing only a particular substrate to bind due to the unique shape and chemical environment created by the enzyme's amino acid side chains.
The breakdown or synthesis of the substrate occurs when it is bound at the active site of the enzyme, forming an enzyme-substrate complex. Once the reaction is completed, the product is released, and the enzyme remains unchanged and ready to catalyze another reaction. This specificity and efficiency of enzymes are crucial for various applications, including the food and pharmaceutical industries, and biological processes within living organisms.