3.2. Factors that affect enzyme action
A subsection of Biology, 9700, through 3. Enzymes
Listing 10 of 202 questions
The enzyme, catechol oxidase, causes a brown colour to develop when slices of many fruits, such as apples, are exposed to air. The enzyme catalyses the following reaction: catechol oxidase catechol + oxygen quinone + water Quinone is then immediately further oxidized in air to a brown-coloured substance. Catechol and quinone are colourless. A student investigated the rate of this reaction under different conditions. State how the student could follow the progress of this reaction. In the first investigation, the student measured the initial rate of the reaction in varying concentrations of catechol. The results are shown in . concentration of catechol / mM initial rate of reaction / arbitrary units Explain the results shown in . In a second investigation, the student repeated the experiment, but this time added a competitive inhibitor, para-hydroxybenzoic acid (PHBA), to each reaction mixture. Sketch on the results that would be obtained for this second investigation. Explain the effect that PHBA will have on the action of phenoloxidase. Lemon juice contains citric acid. Adding even a small amount of diluted lemon juice to apple slices slows the appearance of the brown colour. Suggest an explanation for this observation.
9700_s13_qp_23
THEORY
2013
Paper 2, Variant 3
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202