3. Enzymes
A section of Biology, 9700
Listing 10 of 276 questions
In an investigation, the same concentration of the enzyme phosphorylase was added to different concentrations of glucose phosphate and incubated at 30 °C. At 1 minute intervals, one drop of the reaction mixture was removed and added to a drop of iodine solution on a white tile. The diagram shows the results of this investigation. 10 15 20 25 30 35 concentration of glucose phosphate / mg dm–3 time / minutes colour of iodine solution brown black What explains the trend in the results of this investigation?
9700_s19_qp_11
MCQ
2019
Paper 1, Variant 1
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Use Proteases that work in alkaline conditions are made in large quantities for use in the detergent industry. The microorganism that is generally used for this is the bacterium Bacillus subtilis. An investigation was carried out to compare three potential production methods: ● using free cells of B. subtilis ● using B. subtilis cells immobilised in cubes of agar ● using B. subtilis cells immobilised in beads of sodium alginate. To immobilise the cells in agar, the agar was dissolved and cooled. A suspension of B. subtilis was then added. The agar-bacterium mixture was poured into sterile dishes and allowed to solidify. It was then cut into cubes with sides of 2 mm. Explain why the agar was cooled before the suspension of B. subtilis was added. Describe how cells of B. subtilis could be immobilised in beads of alginate. A liquid medium containing glucose, a nitrogen source and various mineral ions was made up, and 50 cm3 placed into each of three flasks. Samples of a culture of free cells of B. subtilis, agar cubes containing immobilised B. subtilis and alginate beads containing B. subtilis were placed in the three flasks. Each flask contained the same number of bacteria. All the flasks were incubated at 37 °C for 48 hours. Samples of the liquid medium in each flask were taken at six hourly intervals and the concentration of protease measured. The results are shown in . Examiner’s Use free cells cells in agar cubes cells in alginate beads Key: time / hours concentration of protease / arbitrary units With reference to , compare the results for the free cells of B. subtilis and cells immobilised in alginate beads. Examiner’s Use Suggest why lower concentrations of protease were produced by B. subtilis immobilised in agar cubes than B. subtilis immobilised in alginate beads. Two new cultures of immobilised B. subtilis were set up as described in . However, this time a repeat batch fermentation method was used, in which the liquid medium was replaced every 24 hours. This was continued until the cubes or beads had begun to disintegrate. The results are shown in Table 3.1. Table 3.1 number of batches before cubes or beads disintegrated total fermentation time / hours total protease produced / arbitrary units mean productivity of protease / arbitrary units per hour agar cubes 12.44 alginate beads 15.11 With reference to Table 3.1 calculate the percentage increase in the total protease produced when the bacteria were immobilised in alginate rather than agar. Show your working. explain why using bacteria immobilised in alginate rather than agar would be a more cost-effective production of protease.
9700_w09_qp_41
THEORY
2009
Paper 4, Variant 1
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Glucose is used in the synthesis of amylose. Glucose is first converted to glucose 1‑phosphate (G 1‑P). Starch phosphorylase is an intracellular enzyme that can catalyse the synthesis of amylose from G 1‑P, which is the substrate for the reaction: (glucose 1‑phosphate)n amylose + (phosphate ions)n n = a large number Students used a colorimeter to investigate the progress of the reaction. The students made a reaction mixture containing 0.01 mol dm–3 G 1‑P in a buffer solution at pH 6.0. A very small quantity of amylose was added to initiate the reaction. A solution of starch phosphorylase was added to the reaction mixture and samples were taken at 1‑minute intervals. Each sample was added to a dilute iodine solution, stirred and then poured into a cuvette. The absorbance of each solution was recorded. The results of the investigation are shown in . 0.00 0.20 0.40 0.60 0.80 1.00 absorbance 1.20 1.40 1.60 1.80 2.00 time after addition of starch phosphorylase / min Explain why the absorbance increases, as shown in . The students took their final sample at 12 minutes. Predict the results for absorbance if the students had continued to take samples for a further 10 minutes. Explain your answer. prediction explanation State an advantage of using a colorimeter in determining the progress of the reaction. The reaction catalysed by starch phosphorylase occurs at the ends of amylose molecules. Describe the sequence of events that occurs when starch phosphorylase catalyses the addition of a molecule of glucose to the end of an amylose molecule.
9700_w23_qp_23
THEORY
2023
Paper 2, Variant 3
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Questions Discovered
276