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Enzymes [B11] notes page 2
Factors affecting enzyme activity
1. pH – all enzymes have an optimal pH, if the pH is too high or too low the enzyme will denature (change shape)
a. pepsin (stomach) = pH2
b. trypsin (small intestine) = pH8
2. temperature – with increased temperature the reaction rate increases to a maximum point (optimal
temperature). If the temperature gets too high the enzyme will denature (change shape)
3. substrate concentration – the enzyme activity increases as substrate (reactants) concentration increases but
there are only so many enzymes with active sites available so there is a maximum rate
4. enzyme concentration – determined by the cell’s DNA, certain genes are turned on and off to activate or
deactivate enzyme production. Only so many enzymes are made for a cell at one time.
NOTE: enzyme and substrate concentration are directly related
5. competitive inhibitors – a molecule that is very close to the shape of the true
substrate may bind with the enzyme and inhibit the reaction because only binding
between the true substrate and enzyme makes the appropriate products
a. example – carbon monoxide and carbon dioxide. Carbon monoxide is very
similar to carbon monoxide and will bind with haemoglobin
6. non –competitive inhibitors: - including heavy metals (such as lead, mercury and cadmium) – non competitive
molecules bind at the non active (allosteric site) and change the shape of the enzyme so that the substrate can
no longer bind at the active site.