3.1. Mode of action of enzymes
A subsection of Biology, 9700, through 3. Enzymes
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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.
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THEORY
2023
Paper 2, Variant 3
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