The term for the chemical structure that catalyzes biochemical reactions is an enzyme. Enzymes are typically proteins, and they speed up reactions by lowering the activation energy required for the reaction to proceed. Each enzyme is specific to a particular substrate and function, facilitating various metabolic processes within living organisms. Enzymes also play critical roles in digestion, energy production, and cellular signaling. Their activity can be affected by factors such as temperature, pH, and the concentration of substrates and inhibitors.