Role of Enzymes (Edexcel IGCSE Biology: Double Science)

• Enzymes are proteins that act as biological catalysts to speed up the rate of a chemical reaction without being changed or used up in the reaction
• They are biological because they are made in living cells
• Enzymes are necessary to all living organisms as they maintain reaction speeds of all metabolic reactions at a rate that can sustain life
  • For example, if we did not produce digestive enzymes, it would take around 2 - 3 weeks to digest one meal; with enzymes, it takes around 4 hours
  • Often the products of one reaction are the reactants for another (and so on)

The mechanism of enzyme action

• Enzymes are specific to one particular substrate(s) as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate
• When the substrate moves into the enzyme’s active site they become known as the enzyme-substrate complex
• After the reaction has occurred, the products leave the enzyme’s active site as they no longer fit it and it is free to take up another substrate
  • Step One: Enzymes and substrates randomly move about in solution
  • Step Two: When an enzyme and its complementary substrate randomly collide an enzyme-substrate complex forms, and the reaction occurs
  • Step Three: A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions

How enzymes work