Glossary · Sinh học
Enzyme
A biological catalyst, almost always a protein. An enzyme speeds up one specific chemical reaction in the cell without being changed itself, so it can be reused again and again.
An enzyme works by lowering the activation energy of a reaction — the energy threshold that must be crossed for the reaction to happen. It does NOT change the reaction's free energy, so it cannot turn an unfavourable reaction into a favourable one; it only makes a reaction that could already occur happen faster.
The substance an enzyme binds is its substrate. The place on the enzyme where that happens is the active site, where the action takes place.
A cell contains thousands of different types of enzyme molecules, each specific to a particular chemical reaction. OpenStax adds an important qualifier: there is a specifically matched enzyme for each substrate and thus for each chemical reaction — however, there is flexibility as well.