EnzymesEdexcel A-Level Biology B: Flashcards

Exam questions on Enzymes

1. A student investigates catalase, an enzyme in potato tissue that breaks down hydrogen peroxide into water and oxygen. Using a water bath, she mixes potato extract with hydrogen peroxide solution at a series of temperatures and measures the volume of oxygen released during the first 30 seconds. The rate of oxygen release rises up to 40 °C and then falls sharply at higher temperatures.
   Explain why the rate of oxygen release falls sharply at temperatures above 40 °C.2 marks
2. A drug company tests two inhibitors, X and Y, on an enzyme from a pathogen. The rate of reaction is measured at a range of substrate concentrations with no inhibitor, with X and with Y. With X, the rate is much lower at low substrate concentrations, but at very high substrate concentrations it reaches the same maximum rate as with no inhibitor. With Y, the rate is lower at every substrate concentration, and the maximum rate is never reached however much substrate is added.
   Explain how Y reduces the maximum rate of the reaction.2 marks
3. In a bacterium, the amino acid S is made from substance P by a pathway of three enzyme-controlled steps catalysed by E1, E2 and E3. E1 catalyses the first step. When the concentration of S inside the cell rises, the rate of E1 falls, even though S has a completely different shape from P. When the concentration of S falls, the activity of E1 recovers.
   Explain how a rise in the concentration of S reduces the activity of E1.3 marks