What is the difference between competitive and non-competitive enzyme inhibitors?

Both competitive and non competitive inhibitors can affect the rate of an enzyme-substrate reaction. Competitive inhibitors occupy the active site of the enzyme, preventing the substrate from binding. If you increase the substrate concentration in the reaction, the rate of reaction still gradually increases.

A non competitive inhibitor differs, as it binds to the enzyme and changes the shape of the active site, therefore substrate enzyme complexes can not form. An increase in substrate does not increase the rate of reaction

The difference lies in the site that the inhibitor binds to the enzyme at. A competitive enzyme inhibitor will bind to the active site of the enzyme and so directly prevents the substrate from binding to the enzyme. On the other hand, a non-competitive enzyme inhibitor binds to a site other than the active site; consequently causing the conformation of the active site to change, thus the substrate is no longer able to bind to the active site of the enzyme.

Competitive enzyme inhibitors are structurally similar to substrates, and binds to the active site of the enzyme, and work by blocking the normal function at the active site. Non-competitive inhibitors decrease enzyme activity by binding to the enzyme whether or not substrate has bound to the active site, and inhibit the change in enzyme conformational shape necessary for activity.