3. Enzymes
A section of Biology, 9700
Listing 10 of 276 questions
Catalase is an enzyme that catalyses the breakdown of hydrogen peroxide, a toxic waste product of metabolism. catalase 2H2O2 2H2O + O2 shows the results of an investigation into the effect of hydrogen peroxide concentration on the rate of the catalase-controlled reaction, with and without the presence of two different inhibitors. hydrogen peroxide concentration / mmol dm–3 rate of reaction / arbitrary units X Y Z The inhibitors used in the investigation have different modes of action. Identify which of curves X, Y and Z are the results for: • the reaction with the non-competitive inhibitor • the reaction with the competitive inhibitor • the reaction without any inhibitor. non-competitive inhibitor competitive inhibitor without any inhibitor With reference to , compare the maximum rate of reaction, Vmax, and the Michaelis-Menten constant, Km, for curves X, Y and Z. Vmax Km Hydrogen peroxide has a harmful effect on cells. One effect is to damage DNA. Describe the structure of DNA. The cell has mechanisms to repair the damage to DNA caused by hydrogen peroxide. Errors in repair may cause a change to the structure of DNA. Studies have investigated possible risks associated with foods and drinks that contain hydrogen peroxide. This is because the compound can be considered a mutagen. Mutagens cause mutations. Explain why hydrogen peroxide can be considered a mutagen.
9700_m17_qp_22
THEORY
2017
Paper 2, Variant 2
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The unicellular fungus Kluyveromyces lactis is found in dairy products. It is a safe microorganism to culture for the extraction of the enzyme lactase. Lactase catalyses the breakdown of lactose, a sugar found in milk. The reaction catalysed by lactase is summarised in . CH2OH OH OH OH H H H O O H H CH2OH OH OH OH OH H H H O H H CH2OH OH OH OH H H O H H H lactose galactose CH2OH OH OH OH OH H H H O H H product S lactase + + R Describe the reaction that is catalysed by lactase. Use to help you. In your answer, identify R and product S. On a commercial scale, immobilised lactase can be used to produce lactose-free milk. One of the products of the reaction shown in acts as an inhibitor of lactase. This is an example of product inhibition. Suggest why product inhibition is useful in K. lactis when lactase is acting as an intracellular enzyme, but can be a disadvantage when extracted lactase is used free in solution for the production of lactose-free milk. Suggest how using immobilised lactase in a commercial application helps to reduce the problem of product inhibition. The first large-scale production of lactose-free milk with an immobilised enzyme used lactase trapped in cellulose triacetate fibres. Suggest one feature of cellulose triacetate that makes it useful as an immobilising material. For a commercial application using an enzyme, the progress of the enzyme-catalysed reaction needs to be studied. Outline how the progress of an enzyme-catalysed reaction can be investigated experimentally.
9700_m18_qp_22
THEORY
2018
Paper 2, Variant 2
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