What is the difference between competitive and non-competitive inhibition of enzymes?

The main difference is that in competitive inhibition, the inhibitor binds directly to the active site of the enzyme. This therefore prevents the substrate from binding to the enzyme and forming the enzyme-substrate complex. It is directly competing with the substrate. In non-competitive inhibition, the inhibitor binds to a site on the enzyme that is NOT the active site. In doing so, it alters the conformation of the active site, meaning that the substrate can no longer bind to the active site on the enzyme. Competitive inhibition can be overcome by increasing the concentration of the substrate. This cannot occur with non-competitive inhibition.