Enzyme
An enzyme is a protein produced by a living organism that functions as a catalyst.
Mechanism
Enzymes increase the speed and likelihood of chemical reactions within an organism's body by lowering the activation energy necessary for a reaction to occur. This happens because the enzyme selects the particular configuration of the substrate and bends the bonds into the energetically-favorable orientation, with a consequent decrease in entropy. They are essential to all cellular functions, and most life could not exist without them, although viruses lack enzymes, but use them from their host cell.[1] The active site, a three-dimensional structure, is the only region of the enzyme that binds to the substrate. It permits only a particular substrate to bind to the site.[2]