How do enzymes work?

Enzymes are biological catalysts. Like all catalysts they reduce the activation energy required for a reaction to take place without themselves being changed. A reaction is the conversion of a substrate to a product. Before the reaction occurs the enzyme and substrate fit together to form the enzyme-substrate complex. There are two theories as to how the enzyme-substrate complex is formed. The two theories are the lock and key theory and the induced fit theory.The lock and key theory: like a lock and a key the enzyme and substrate fit into each-other perfectly and this combination allows for the reaction being catalysed to occur. The induced fit theory describes the enzyme and substrate being a close match but requiring a small change in shape to fit perfectly. This small change may put strain on a few bonds in the substrate to form the enzyme-substrate complex. Once the enzyme-substrate complex has been created the enzyme alters the substrate in a way that reduces the energy needed to turn it into the product.