Enzymes & pH (Cambridge (CIE) IGCSE Combined Science: Biology): Revision Note

Enzymes & pH: Extended

Extended Tier Only

• The optimum pH for most enzymes is 7 but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2) and some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9)

• If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed

• This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity

• Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop