Enzymes. Enzymes are proteins, produced by living cells; they catalyze chemical reactions by lowering the activation energy. Activation energy is the energy required for a chemical reaction to occur. Enzymes are generally globular proteins with characteristic three-dimensional shapes.The active site is the binding site for the enzyme’s substrate. Enzymes are specific for substrate molecules.ctivation energy is the energy required for a chemical reaction to occur. Enzymes are generally globular proteins with characteristic three-dimensional shapes. The active site is the binding site for the enzyme’s substrate. Enzymes are specific for substrate molecules.