Enzymes as Catalysts

What are the characteristics of enzymes?

As explained previously, enzymes are very specific in their action.

Enzymes and pH

Enzymes are very sensitive to the conditions at which they work. Many enzymes work best at a particular pH and stop working if the pH becomes too acidic or alkaline.

Graph of enzyme-catalysed reaction rate against pH.

 

Enzymes and temperature

Enzymes are also sensitive to temperature. Many work best at temperatures close to body temperatures and most lose their ability to catalyse if they are heated above 60 or 70 degrees Celcius.

Graph of enzyme-catalysed reaction rate against temperature.

 

Why are they sensitive?

The reason why enzymes are so sensitive to changes in pH and temperature is that such change can affect the interactions that hold the parts of the protein chain in place. If the shape of the active site is changed, the substrate molecule will no longer be able to form temporary attractions with the protein chain, because the chemical groups needed to do this will no longer be in the right place. We say that the enzyme has become denatured.