Rate: Enzyme Concentration (Cambridge International AS Biology)

Spec point — investigate and explain the effects of the following factors on the rate of enzyme-catalysed reactions: • enzyme concentration

Rate: enzyme concentration

• Enzyme concentration affects the rate of reaction

• The higher the enzyme concentration in a reaction mixture:

  • The greater the number of active sites available
  • The greater the likelihood of enzyme-substrate complex formation

• As long as there is sufficient substrate available, the initial rate of reaction increases linearly with enzyme concentration

• If the amount of substrate is limited, at a certain point any further increase in enzyme concentration will not increase the reaction rate as the amount of substrate becomes a limiting factor

The effect of enzyme concentration on the rate of an enzyme-catalysed reaction

Exam Hint Always mention substrate availability when explaining the effect of increasing enzyme concentration.

A common mistake is to say that “more enzymes always increase the rate” — but this is only true while there is enough substrate present. In exams, you should state that if substrate becomes limiting, the rate will level off even if enzyme concentration keeps increasing.