Revision-Enzymes II

• As pH increases or decreases, the shape of the enzyme changes until it is the shape at which it is most active (optimal pH). As pH changes further, the shape changes and the activity lessens. The enzyme denatures (becomes inactive) if the pH is too far from optimal.
• The optimal pH for amylase is alkaline (pH 7-8), so amylase is most active in the mouth and duodenum where the pH is in this range. This enzyme is not active in acidic conditions so it is not active in the stomach (pH 1-2). Lipase is also active in the doudenum where the pH is high.
• Pepsin has optimal activity in conditions of low pH, so is active in the acidic stomach.
• Temperature changes can also alter rate of reaction. Amylase is found in the mouth of humans so it is very active at 37 degrees. At low temperatures, particles involved in the reaction move more slowly so there are fewer collisions between starch and enzyme. At temperatures higher than 37 (eg 50 degrees), the enzyme denatures (changes shape) so it cannot catalyse the breakdown of starch.