3. Enzymes
A section of Biology, 9700
Listing 10 of 276 questions
Table 2.1 shows eight ions that are biologically important. Table 2.1 ammonium (NH4 +) A hydrogen (H+) B hydrogen carbonate (HCO3 –) C iron (Fe2+) D magnesium (Mg2+) E nitrate (NO3 –) F phosphate (PO4 3–) G sulfate (SO4 2–) H Choose one ion to match each of the following statements. In each case write one letter from Table 2.1. You may use each letter (A to H) once, more than once or not at all. A component of polynucleotides. Ion produced by enzyme activity inside red blood cells. Ion used in the production of all amino acids in chloroplasts. Ion that diffuses through carrier proteins with sucrose into companion cells in phloem tissue. Component of haem group in haemoglobin that binds oxygen. The enzyme nitrogenase is found in free-living and symbiotic nitrogen-fixing bacteria. Nitrogenase catalyses the reaction: N2 + 6 e– + 8H+ 2NH4 + Some nitrogenase enzymes have vanadium ions in their active sites; others have molybdenum ions. Explain how the enzyme nitrogenase functions in the fixation of nitrogen. Some pea plants were grown with their roots in a solution of mineral ions. The solution was kept aerated for three days. The concentrations of five ions in the solution and in the root tissue were determined after the three days. The results are shown in Table 2.2. Table 2.2 ion concentration / mmol dm–3 surrounding solution root tissue potassium (K+) 1.0 75.0 magnesium (Mg2+) 0.3 3.5 calcium (Ca2+) 1.0 2.0 phosphate (PO4 3–) 1.0 21.1 sulfate (SO4 2–) 0.3 19.7 With reference to Table 2.2, suggest how cell surface membranes of root cells are responsible for the concentrations of ions in the roots compared to the surrounding solution.
9700_w13_qp_21
THEORY
2013
Paper 2, Variant 1
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Ethylene glycol is a chemical used to prevent water from freezing. If ethylene glycol is swallowed accidentally, it is metabolised by an enzyme found in liver cells to produce a toxic product. The enzyme normally catalyses the oxidation of ethanol to a harmless product. People who have swallowed ethylene glycol are treated with large doses of ethanol. This prevents formation of a toxic product and allows the body to excrete the ethylene glycol. Which statement describes why this treatment works?
9700_w14_qp_11
MCQ
2014
Paper 1, 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
276