Cambridge IGCSE Biology: Enzyme Action Study Guide

Examination Details for Cambridge Assessment 0610/32

  • Examination Provider: Cambridge Assessment International Education.
  • Candidate Identification: Space is provided for the Candidate Number and Center Number on the front cover.
  • Paper Reference: 0610/320610/32.
  • Series: February/March 2025.
  • Duration: The total time allotted for the examination is 1 hour 15 minutes1\,hour\,15\,minutes.

Biological Catalysts and Enzymes

  • Definition of an Enzyme: Enzymes are proteins that function as biological catalysts, meaning they speed up the rate of chemical reactions within living organisms without being consumed or permanently altered in the process.
  • Enzyme Specificity: Each enzyme is specific to a particular substrate due to the unique three-dimensional shape of its active site.

Structural Components of Enzyme Action (Fig. 1.1)

  • The Enzyme Molecule: Represented in Fig. 1.1 as the larger structure with a specific indentation or cleft known as the active site.
  • The Substrate Molecule: Represented as the smaller molecule that is intended to undergo a chemical transformation. In the diagram, the substrate has a specific geometric shape that is complementary to the active site of the enzyme.

The Mechanism of Enzyme Action

  • Molecular Collision: For a reaction to occur, the substrate molecule must collide with the enzyme molecule with sufficient energy and in the correct orientation.
  • Complementary Shapes: The shape of the substrate is complementary to the shape of the active site of the enzyme. This is often likened to a "lock and key" mechanism, where the enzyme is the lock and the substrate is the key.
  • Formation of the Enzyme-Substrate Complex:
    • The substrate moves into the active site of the enzyme.
    • The substrate binds to the active site, forming a temporary intermediate structure called the enzyme-substrate complex.
  • Catalysis and Product Formation:
    • While the substrate is held in the active site, chemical bonds within the substrate are broken or new bonds are formed.
    • The substrate is converted into one or more products.
  • Product Release: Once the reaction is complete, the products no longer fit the active site perfectly and are released into the surrounding medium.
  • Enzyme Conservation: The enzyme remains unchanged at the end of the reaction. Its active site is now vacant and ready to accept another substrate molecule, allowing the process to repeat many times.

Summary of Enzyme Characteristics Demonstrated

  • Active Site: The specific region where catalysis occurs.
  • Binding: The physical attachment of the substrate to the protein structure of the enzyme.
  • Transformation: The conversion of the substrate into products while the enzyme acts as a scaffold for the reaction.