Many Proteins are Enzymes (AQA AS Biology): Revision Note

Enzymes as proteins

• Enzymes are globular proteins

• They act as biological catalysts

  • ‘Biological’ because they function in living systems

  • ‘Catalysts’ because they speed up the rate of chemical reactions without being used up or changed

• Critical to the enzyme's function is the active site where the substrate binds

• Metabolic pathways are controlled by enzymes in a biochemical cascade of reactions

  • Virtually every metabolic reaction within living organisms is catalysed by an enzyme; enzymes are therefore essential for life to exist

• Enzymes can be intracellular or extracellular, and these determine the structures and functions from the cellular to the whole-organism level

  • Intracellular enzymes are produced and function inside the cell

  • Extracellular enzymes are secreted by cells and catalyse reactions outside cells (e.g. digestive enzymes in the gut)