Effect of Temperature and pH on Enzyme Activity

Learning Intention: Students will understand that enzymes are proteins and biological catalysts that speed up chemical reactions in living organisms. They will also understand two of the factors that affect the action of enzymes, temperature and pH.

Success Criteria: Students will be able to design, perform, describe and report on an experimental procedure demonstrating the effect of temperature and pH on enzyme activity.

Students used potato, alfalfa sprouts and liver extract (most successful) to demonstrate how catalase (enzyme) breaks down hydrogen peroxide (H2O2) into water and oxygen. This process is essential to maintain a safe and healthy internal environment. When hydrogen peroxide was added to the liver extract and different concentrations of HCl (distilled water, 0.01M, 0.05M, 0.1M, 0.5M and 1.0M hydrochloric acid), only the distilled water and 0.01M HCl tubes released significant quantities of oxygen. At higher acid concentrations (lower pH) no enzyme activity was apparent, because the acid destroys the protein or denatures the enzyme.

Diastase is an enzyme that catalyses the conversion of starch (polysaccharide) into sugars (di- and mono-saccharides). Iodine is an indicator that turns from yellow to blue-black in the presence of starch. Students used two sets of five test tubes with 10 ml of starch solution in each. In the control set, distilled water was added to to each test tube. In the second set, the enzyme diastase was added. One tube from each set was then placed into water baths at different temperatures (room temp, 40C, 60C, 80C and 100C). Iodine was used to indicate which tubes contained active enzyme. If the tube contained starch, the colour was blue-black, indicating that there was little or no enzyme activity (control tubes). The lighter the colour, the greater the conversion, therefor the more enzyme activity. The tubes at room temperature, 40C and 60C showed the most enzyme activity.

 

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