3.1. Mode of action of enzymes
A subsection of Biology, 9700, through 3. Enzymes
Listing 10 of 74 questions
Biofuels contain alcohols that are produced by the fermentation of sugars derived from crop waste. This waste contains cellulose and other organic compounds in cell walls. Scientists investigated the production of sugars from crop waste for biofuel production. The scientists discovered that a strain of the fungus Penicillium citrinum, isolated from soil, was a good source of three different extracellular enzymes, M, N and O. These enzymes break down polysaccharides in cell walls. The scientists cultured P. citrinum in a liquid medium containing cell wall material. Samples of the liquid were taken, and the three enzymes were separated from the medium. Each enzyme was placed in a reaction mixture with an appropriate substrate. The activity of each enzyme was determined to give a measurement of the quantity of enzyme produced by P. citrinum. The results are shown in Table 4.1. Table 4.1 enzyme maximum activity / arbitrary units M 292.83 N 111.72 O 6.54 Optimum conditions for each enzyme were used to obtain the results in Table 4.1. The conditions were different for each enzyme. The scientists carried out further research so that a solution containing the three enzymes (enzyme mixture) could be used for the most efficient production of sugars from crop waste. Suggest what the scientists needed to find out in their research. Students investigated the composition of the cell wall of leaf cells of thale cress, Arabidopsis thaliana. The students began by isolating the cell wall components from the rest of the cell material. The students used enzymes extracted from a fungal pathogen of A. thaliana to hydrolyse the cell wall components to smaller molecules. The students prepared a reaction mixture containing the cell wall components and the enzymes. After 24 hours, they separated and identified the smaller molecules found in the reaction mixture. Four types of molecule were identified: • short chains of β-glucose • β-glucose • peptides • amino acids. Explain the presence of these molecules in the reaction mixture after 24 hours of hydrolysis.
9700_w24_qp_23
THEORY
2024
Paper 2, Variant 3
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A scientist investigated the progress of two enzyme-catalysed reactions in separate test-tubes, X and Y. Both reactions result in colour changes that can be detected using colorimetry. 0.5 cm3 samples were taken from each test-tube at the start of the investigation and at regular intervals for the next 5 minutes. Copper ions were added to each sample as soon as the sample was collected to inactivate the enzymes and stop the reactions from progressing further. The absorbance of each sample was measured using a colorimeter. The graph shows the results of this investigation. percentage absorbance time / minutes X Y Which statement is consistent with the results shown...
9700_m24_qp_12
MCQ
2024
Paper 1, Variant 2
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The enzyme sucrase catalyses the breakdown of the glycosidic bond in sucrose. A student investigated the effect of increasing the concentration of sucrose on the rate of activity of sucrase. Ten test-tubes were set up with each containing 5 cm3 of different concentrations of a sucrose solution. The test-tubes were placed in a water bath at 40 °C for ten minutes. A flask containing a sucrase solution was also put into the water bath. After ten minutes, 1 cm3 of the sucrase solution was added to each test-tube. The reaction mixtures were kept at 40 °C for a further ten minutes. After ten minutes, the temperature of the water bath was raised to boiling point. Benedict’s solution was added to each test-tube. The time taken for a colour change was recorded and used to calculate rates of enzyme activity. The results are shown in . concentration of sucrose / g dm–3 rate of enzyme activity / arbitrary units Name the type of reaction catalysed by sucrase. Explain why the temperature of the water was raised to boiling point. Describe and explain the results shown in .
9700_s11_qp_21
THEORY
2011
Paper 2, Variant 1
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Questions Discovered
74