What factors affect enzyme activity?

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Enzyme activity is affected by various factors, including substrate concentration and the presence of inhibiting molecules.
The rate of an enzymatic reaction increases with increased substrate concentration, reaching maximum velocity when all active sites of the enzyme molecules are engaged. Thus, enzymatic reaction rate is determined by the speed at which the active sites convert substrate to product.
Inhibition of enzyme activity occurs in different ways. Competitive inhibition occurs when molecules similar to the substrate molecules bind to the active site and prevent binding of the actual substrate.
Noncompetitive inhibition occurs when an inhibitor binds to the enzyme at a location other than the active site.
Another factor affecting enzyme activity is allosteric control, which can involve stimulation of enzyme action as well as inhibition. Allosteric stimulation and inhibition allow production of energy and materials by the cell when they are needed and inhibit production when the supply is adequate.