Enzyme activity is affected by factors such as substrate concentration, enzyme concentration, temperature and pH.

As substrate concentration increases there is more substrate molecules colliding with active sites per second

. As substrate concentration continues to increase, rate of reaction does not increase indefinitely and Vmax is reached.

sub conc


A fixed enzyme concentration means a fixed number of active sites.  Therefore as substrate concentration increases, there would come a point in time where there would be no available active sites. This is called satuaration. Substrates would therefore need to ‘wait’ for an active site.

As temperature increases, rate of reaction reaction increases.

Rate of reaction reaction increases because of two things:

1) incease in collision frequency between molecules

2) more substrate molecules will have the energy to overcome the actvation barrier, increasing rate of reaction. Reaction rate decreases as temperature increases over optimum temperature. Enzymes can no longer function because the active site has been denatured and its shape changes.

Graph of enzyme activity verses temperature

Optimum pH varies for different enzymes.

The pH at which maximal enzyme activity is achieved is different for different enzymes, and reflects the H+ concentration at which enzyme function in the body.
Each enzyme works within a small pH range.Extremes of pH can lead to denaturation of the enzyme. This is due to the fact that the structure of protein depends on the ionic character of the amino acid side chains.

Graph of enzyme activity verses pH


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