see also : [[digestion]] [[cells + movement across membranes]]
Enzymes increase the rate of a reaction without being permanently altered themselves. They are biological catalysts and are crucial to living organisms (enable cellular reactions to take place at lower temperatures). Enzymes are proteins made up of a chain of amino acids. The order of amino acids determines how the amino acid chain folds and its structure. Its function is determined by the shape of the enzyme. The region of an enzyme to which a substrate molecule binds is called the active site. The active site shape is specific to the substrate molecule. Each enzyme is complementary to only one type of substrate (described as having a ‘high specificity’). ● Substrate collides with the active site of an enzyme ● Substrate binds, enzyme-substrate complex forms ● Substrate converted to products ● Products are released from the active site. The active site is now free to bind to another substrate This is the ‘lock and key’ hypothesis.