3.1. Mode of action of enzymes
A subsection of Biology, 9700, through 3. Enzymes
Listing 10 of 74 questions
The induced-fit hypothesis and the lock-and-key hypothesis are used to describe the mode of action of enzymes. Explain the induced-fit hypothesis. Radish plants contain the enzyme peroxidase that catalyses the breakdown of hydrogen peroxide. Students investigated the effect of increasing the concentration of hydrogen peroxide on the activity of peroxidase extracted from radish. The results of their investigation are shown in . 0.00 0.10 0.20 0.30 concentration of hydrogen peroxide / mmol dm–3 0.40 0.50 0.60 initial rate of reaction / μmol min–1 Explain the effect of increasing the concentration of hydrogen peroxide on the initial rate of reaction as shown in . The students determined the Km for radish peroxidase as 0.10 mmol dm–3. With reference to , describe how they determined the Km. A further investigation found that the Km for carbonic anhydrase is 12 mmol dm–3. Describe the role of carbonic anhydrase in the transport of carbon dioxide.
9700_s21_qp_21
THEORY
2021
Paper 2, Variant 1
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is a computer-generated image of the enzyme hexokinase binding with its substrate, glucose. The product of the enzyme-catalysed reaction is glucose-6-phosphate. glucose hexokinase Hexokinase binds with glucose using the induced fit mechanism. Describe how an enzyme-substrate complex forms by this mechanism. Suggest how enzymes which use the induced fit mechanism can be less affected by competitive inhibitors than those which use the lock and key mechanism. When a solution of the enzyme hexokinase is heated to 45 °C for 10 minutes, the quantity of product formed decreases by 50% compared to a sample kept between 30 °C and 40 °C. Explain this result. Glucose can enter cells by active transport or facilitated diffusion. Glucose-6-phosphate is a charged, polar molecule and cannot move out of cells. State two differences between active transport and facilitated diffusion. 1. 2. Suggest why glucose-6-phosphate cannot move out of cells.
9700_w14_qp_23
THEORY
2014
Paper 2, Variant 3
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The pollutants in waste water from the textile industry may include azo-dyes, which give colour to textiles. Azo-dyes are organic pollutants that can be carcinogenic. White-rot fungi are useful for the treatment of environmental pollution as they produce extracellular enzymes that are able to break down a number of organic pollutants, such as azo-dyes. The extracellular enzymes produced by white-rot fungi are primary metabolites that are mass produced by continuous culture. Outline the main operating conditions of continuous culture. State three advantages of using continuous culture and not batch culture, for the mass production of these enzymes. The ability of the white-rot fungi to break down azo-dyes was investigated. A suspension of the intact fungal cells was added to water contaminated with various concentrations of an azo-dye. The results are shown in Table 5.1. Table 5.1 percentage breakdown of azo-dye azo-dye concentration / mg dm–3 after 7 days after 10 days 21.9 100.0 53.1 93.7 61.7 89.6 51.0 87.3 Describe the results shown in Table 5.1. When a similar experiment was performed using the free enzymes from the white-rot fungal cells, all concentrations of azo-dye shown in Table 5.1 were broken down within 12 hours. Suggest why free enzymes break down the azo-dye more quickly than intact white-rot fungal cells. These extracellular enzymes may be immobilised on an inert support. Outline the advantages of using immobilised enzymes in the treatment of textile waste water.
9700_w14_qp_43
THEORY
2014
Paper 4, Variant 3
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Questions Discovered
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