Enzyme Activity

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•  Temperature, pH and substrate concentration affect the rate of activity of enzymes

Various factors may affect the activity of enzymes, by either affecting the frequency of enzyme-substrate collisions or by affecting the capacity for the enzyme and substrate to interact (e.g. denaturation)

  • Temperature, pH and substrate concentration will all influence the rate of activity of an enzyme


  • Low temperatures result in insufficient thermal energy for the activation of an enzyme-catalysed reaction to proceed
  • Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity
  • This is because a higher kinetic energy will result in more frequent collisions between the enzymes and substrates
  • At an optimal temperature (may vary for different enzymes), the rate of enzyme activity will be at its peak
  • Higher temperatures will cause enzyme stability to decrease, as the thermal energy disrupts the enzyme’s hydrogen bonds
  • This causes the enzyme (particularly the active site) to lose its shape, resulting in the loss of activity (denaturation)

The Effect of Temperature on Enzyme Activity

enzyme temperature


  • Changing the pH will alter the charge of the enzyme, which in turn will alter protein solubility and overall shape
  • Changing the shape or charge of the active site will diminish its ability to bind the substrate, abrogating enzyme function
  • Enzymes have an optimal pH (may differ between enzymes) and moving outside this range diminishes enzyme activity

The Effect of pH on Enzyme Activity

enzyme pH

Substrate Concentration

  • Increasing substrate concentration will increase the activity of a corresponding enzyme
  • More substrates mean there is an increased chance of enzyme and substrate colliding and reacting within a given period
  • After a certain point, the rate of activity will cease to rise regardless of any further increases in substrate levels
  • This is because the environment is saturated with substrate and all enzymes are bound and reacting (Vmax)

The Effect of Substrate Concentration on Enzyme Activity

enzyme substrate concentration