Factors Affecting Enzyme Activity

Four factors that affect enzyme activity are:

  • Temperature
  • pH
  • Enzyme concentration
  • Substrate concentration

To consider how these factors affect enzyme activity, it is important to know how to calculate the rates of a chemical reaction.

Diagram showing that rate of reaction is equal to the amount of substrate used or amount of subsrate formed divided by the time taken

So to calculate the rate of an enzyme-catalysed reaction, we are measuring either the rate at which the substrate is used up or the rate at which the substrate is formed.

Temperature

As the temperature increases, the rate of enzyme activity increases. Or in other words, as the temperature increases, the rate of reaction increases. A higher temperature results in higher kinetic energy. As the kinetic energy increases, there are more collisions between the enzymes and substrates.

However, this only happens up until an optimum point, which is the point at which enzymes are working at their fastest. At this point, there is the maximum frequency of collisions between the enzymes and substrates.

  • The optimum body temperature in humans is approximately 37°C, so this is the temperature at which enzymes in the body work best. The temperature varies with different organisms.

Once the temperature increases past the optimum, the rate of reaction decreases rapidly. Then the reaction will eventually stop as the temperature becomes too high.

At this point, the bonds that hold the enzyme together will begin to break, so the shape of the active site is altered. Therefore, the substrate can no longer bind with the enzyme and the enzyme is said to be denatured, which means it can no longer catalyse the reaction.

Diagram showing the relationship between the rate of reaction and rise in temperature

pH

Most enzymes have an optimum pH of 7, which is neutral. However:

  • Some enzymes have a lower optimum pH (so they work best in acidic conditions) – For example, protease enzymes in the stomach.
  • Some enzymes have a higher optimum pH (so they work best in alkaline conditions) – For example, duodenum.

The bonds that hold the amino acid chains in the enzyme together are affected by the pH. If we make the pH more acidic or alkaline, then the enzyme activity drops to zero. This is because the shape of the active site has changed.

If the active site changes, then the substrate can no longer fit in the enzyme’s active site. So, the enzyme is denatured, meaning that it can no longer work.

Diagram showing the relationship between the rate of reaction and rise in PH.

Enzyme Concentration

In a fixed concentration of enzymes, as the substrate concentration increases, the rate of reaction will also increase.

However, this is up until a certain point. Eventually, the active sites of the enzymes will become occupied, which is the saturation point. After this point, the rate of reaction will remain constant, even if there is plenty of substrate remaining.

Diagram showing the relationship between the rate of reaction and enzyme concentrate

Substrate Concentration

An optimum substrate concentration is needed for enzymes to work properly.

In a fixed concentration of substrate, as the enzyme concentration increases, the rate of reaction will also increase up to a particular point.

In this case, the concentration refers to the concentration of the substance binding to the enzyme. This is due to the fact that as the substrate concentration increases, the rate at which enzymes collide with substrates also increases. However, once all the substrate has been used up, the reaction will stop.

Diagram showing the relationship between the rate of reaction and substrate concentration

You’ve used 10 of your 10 free revision notes for the month

Sign up to get unlimited access to revision notes, quizzes, audio lessons and more

Sign up