An enzyme is a protein (or, in rare cases, an RNA molecule) that catalyzes a specific chemical reaction — it speeds the reaction up without being consumed in the process. Nearly every chemical reaction in a living cell is catalyzed by an enzyme. Without enzymes, metabolic reactions would occur too slowly to sustain life.
Enzymes work by lowering the activation energy of a reaction — the energy barrier that must be overcome for the reaction to proceed. Each enzyme has an active site, a region whose shape and chemical properties are complementary to the substrate (the molecule it acts on). The substrate binds to the active site, the enzyme facilitates the chemical transformation, and the product is released. This specificity means that each enzyme typically catalyzes only one reaction or a narrow class of reactions. The human body produces thousands of different enzymes, each tailored to its particular reaction.
Enzyme activity is regulated. Temperature and pH affect enzyme shape and function — each enzyme has an optimal range outside of which it denatures (loses its functional shape). Allosteric regulation occurs when molecules bind to sites other than the active site, changing the enzyme’s shape and activity. Feedback inhibition — where the end product of a metabolic pathway inhibits an enzyme earlier in the pathway — is a fundamental mechanism of homeostatic regulation at the molecular level.
Enzymes are central to decomposition, digestion, DNA replication, protein synthesis, and virtually every other biological process. Saprotrophic fungi digest their substrates by secreting enzymes externally — a strategy called extracellular digestion. Restriction enzymes in bacteria cut foreign DNA at specific sequences. Industrial applications of enzymes include brewing, cheese-making, and laundry detergents.
Related terms
- Metabolism — the network of enzyme-catalyzed reactions sustaining life
- Cell — the site of enzymatic activity
- DNA — both a product of enzymatic activity and a template for enzyme production
- Gene — the DNA segment encoding each enzyme
- Homeostasis — maintained in part through enzyme regulation