Protein or protein-based molecules that speed up chemical reactions occurring in living things.
Enzymes act as catalysts for a single reaction, converting a specific set of reactants (called substrates) into specific products. They lower the activation energy, so that chemical reactions can occur at room temperature.
The increase in rate can be as much as 1010 times that of the reaction without the enzyme present.
All cellular reactions are controlled by enzymes and without enzymes life as we know it would be impossible.
The specific molecule(s) acted upon by an enzyme.
See also: Active Site, Anaplerotic Reaction, Coenzyme, Helicase, Isozymes, Kinases, Krebs Cycle, Lock and Key Model, Lyases, Lysosomal Enzymes, Oxygenases, Regulatory Enzyme, Turnover Number, Zymogen.