Enzymes or biocatalysts are proteinaceous substance that are capable of catalysing chemical reactions of biological systems without themselves undergoing any change. The graph x shows normal enzyme reaction, graph y shows competitve inhibition and graph z shows non competitive inhibition. In competitive inhibition the inhibitor, which is a substrate analogue, combines reversibly to the free enzyme at the active site. In non competitive inhibition, the inhibitor binds to enzyme at a place other than substrate binding site. It results in destruction of enzyme activity.