Enzymes as Catalysts

Breaking down hydrogen peroxide

In this section we look at how hydrogen peroxide is broken down

  • in our bodies
  • in the bombardier beetle
  • to clean contact lenses

In our bodies

Our bodies make use of very many enzymes to catalyse specific reactions. We rely on them to keep our bodies working.
Hydrogen peroxide is produced by reactions in our bodies. If it were allowed to build up it would kill us. Fortunately we have an enzyme in the cells in our bodies where hydrogen peroxide is produced called catalase. This enzyme catalyses the breakdown of hydrogen peroxide into harmless water and oxygen.


catalase

 

H2O2

H2O + O2

In the bombardier beetle

The bombardier beetle lives in South America and relies on the enzyme catalysed decomposition of hydrogen peroxide to defend itself against predators.

The beetle has a gland on the tip of its abdomen that contains two chambers. One chamber contains a mixture of hydroquinone and hydrogen peroxide and the other contains a mixture of two enzymes, catalase and peroxidase. When the beetle is threatened it mixes the contents of the two chambers. The enzymes catalyse the decomposition of hydroquinone and of hydrogen peroxide. Both of these reactions are exothermic so the mixture gets hot. The oxygen from the decomposition of the hydrogen peroxide builds up a pressure that is used by the beetle to spray its attacker with a stream of hot, corrosive liquid.

A bombadier beetle.

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