Knowing More About Enzymes

Information is adapted from

Secondary 1/2 Level

What are enzymes?

  • All enzymes are globular proteins → spherical in shape (Fig 3)
  • Control biochemical reactions in cells
  • They have the suffix “-ase
  • Intracellular enzymes are found inside the cell
  • Extracellular enzymes act outside the cell (e.g. digestive enzymes)
  • Enzymes are catalysts → speed up chemical reactions (Fig 1 & Fig 2)
    • Reduce activation energy required to start a reaction between molecules
    • Substrates (reactants) are converted into products
    • Reaction may not take place in absence of enzymes (each enzyme has a specific catalytic action)
    • Enzymes catalyse a reaction at max. rate at an optimum state













Lock and key theory

  • Only one substrate (key) can fit into the enzyme’s active site (lock)
  • Both structures have a unique shape
  • Enzyme is not used up in the reaction (unlike substrates)

Enzyme Activity

  • Changes in pH
    • Ionic bonds can break and change shape → enzyme is denatured (not able to perform its intended function)
    • Optimum pH (enzymes work best)
      • pH 7 for intracellular enzymes
      • Acidic range (pH 1-6) in the stomach for digestive enzymes (pepsin)
      • Alkaline range (pH 8-14) in oral cavities (amylase)
    • pH measures the conc. of hydrogen ions → higher conc. will give a lower pH
  • Increased Temperature
    • Increases speed of molecular movement → chances of molecular collisions
    • At 0-42°C rate of reaction is proportional to temp
    • Enzymes have optimum temp. for their action (usually 37°C in humans)
    • Above ≈42°C, enzyme is denatured due to heavy vibration that breaks -H bonds
    • Shape is changed → active site can’t be used anymore
  • Decreased Temperature
    • Enzymes become less and less active, due to reductions in speed of molecular movement
    • Below freezing point
      • Inactivated, not denatured
      • Regain their function when returning to normal temperature


Secondary 3/4 Level