Effect of Temperature

  • Increasing temperature increase rate of reaction
  • Particles move faster and are therefore more likely to collide
  • Temperature coefficient, Q10 = how much the rate of reaction increases with a 10℃ rise. (usually doubles)
  • Optimum temperature is the temperature at which the rate of reaction is fastest
  • Past optimum, the bonds holding the enzyme together vibrate, and eventually denature permanently.


  • Organisms adapted to living in very hot temperatures
  • Enzymes are more stable and shapes are more resilient to change
  • More disulphide bridges are present

Cold environments

  • Some enzymes have more flexible structures, and are therefore less stable
  • Small temperature changes will denature them

Effect of pH

  • H⁺ ions decrease the pH
  • Optimum pH is the level at which the rate of reaction is greatest
  • H⁺ interacts with polar groups and charged R groups, causing bonds to break and substrate no longer fits into active site when pH is far from optimum

Substrate concentration and enzyme concentration


  • As substrate concentration increases, the number of substrate molecules/atoms/ions in an area/volume increases

    • The same is true for enzyme concentration
  • Increased chance of successful collisions

  • Vmax is the maximum rate of reaction

    • It occurs when all active sites are occupied by substrate particles.


  • Increasing enzyme concentration increases the number of active sites available
  • This increases the number of enzyme-substrate complexes that can be formed, increasing the rate of reaction
  • Vmax can be increased by increasing the substrate concentration and/or temperature