Question

c) i) what would happen to an enzyme if the temperature and ph changed significantly beyond the enzymes optimum level?

ii) how would this affect enzyme activity?

a group of students decided to carry out an investigation to find out how enzyme activity is affected by temperature changes. they put samples of salivary amylase and starch into two test tubes. salivary amylase is an enzyme that breaks down starch into maltose. its optimum temperature for activity is around 37°c.

a) what do you think happened to the rate of reaction when they increased the temperature of the first test tube to 37°c?

b) what do you think happened to the enzyme activity when the students decreased the temperature of the second test tube to 0°c?

Explanation:

• c i: Enzymes are proteins. High temperatures (beyond optimum) break the bonds (hydrogen bonds, ionic bonds etc.) that maintain the enzyme's 3 - D structure (denaturation). Extreme pH (beyond optimum) also disrupts these bonds (e.g., by protonating or de - protonating amino acid side chains) leading to a change in the enzyme's shape.
• c ii: The enzyme's active site (the region where the substrate binds) is part of its 3 - D structure. When the shape of the enzyme changes (due to temperature or pH changes beyond optimum), the substrate may no longer fit into the active site (lock - and - key model). So, the enzyme cannot catalyze the reaction, and enzyme activity stops (or is severely reduced).
• a: Since \(37^{\circ}C\) is the optimum temperature for salivary amylase, at this temperature, the enzyme molecules have the right amount of kinetic energy. The enzyme - substrate collisions are maximized, and the enzyme's active site is in the best conformation to bind the substrate (starch). So, the rate of reaction (breakdown of starch into maltose) is maximized.
• b: At \(0^{\circ}C\), the enzyme (salivary amylase) is not denatured. But the kinetic energy of both the enzyme and the substrate (starch) molecules is very low. There are fewer enzyme - substrate collisions. So, the enzyme activity is very low (the reaction almost stops, but the enzyme can regain activity when the temperature is raised again).

Answer:

• c i) The enzyme would denature (its shape would change due to bond breakage).
• c ii) Enzyme activity would stop (or be severely reduced) as the substrate can no longer bind to the active site.
• a) The rate of reaction would be maximized.
• b) Enzyme activity would be very low (the reaction almost stops, but the enzyme is not denatured).