What is the difference between a competitive and a non-competitive inhibitor?

Inhibitors are molecules that stop substrates from being able to bind to their enzymes, and therefore inhibit the action of specific enzymes. A competitive inhibitor is an inhibitor which has a similar shape to the substrate; it is complementary, so can bind to the active site of the enzyme, preventing the substrate from binding. However, the inhibitor can eventually be "knocked out" of the active site, allowing the original substrate to bind. This means enzyme catalysed reactions can take place, just at a much slower rate. THE INHIBITOR AND SUBSTRATE ARE IN COMPETITION WITH EACH OTHER FOR THE ACTIVE SITE. Non-competitive inhibitors may or may not have a similar shape to the substrate, but these bind to a site on the enzyme other than the active site; this is called a binding site. After binding, the tertiary structure of the enzyme is distorted, and therefore the shape of the active site changes. The substrate is no longer complementary to the active site, and therefore cannot bind to it. The inhibitor cannot be "knocked out" either.