Explain how a competitive inhibitor stops an enzyme from working.

Enzymes are proteins that act as biological catalysts: they increase the rate of reactions without being used up themselves. A region on the enzyme, known as the active site, is very specific and complementary to the shape of the substrate molecule. When a substrate binds to a complementary enzyme, an enzyme-substrate complex is formed and a chemical reaction takes place. This leads to the formation of products.

A competitive inhibitor has a similar shape to the substrate, this means that it is capable of binding to the active site of the enzyme as it is complementary to it. Therefore, fewer substrate molecules bind to the enzyme and so fewer enzyme-substrate complexes can form. This leads to fewer products being formed. If the concentration of the competitive inhibitor is high enough, substrate molecules will be unable to bind to the enzyme resulting in no products being formed. The enzyme will be unable to perform its function.