本题目来源于试卷: Interaction & Interdependence C.1 Enzymes & Metabolism，类别为 IB生物学
[单选题]
The graph shows the effect hb vlyma;,5du6-q j*+,jb dmwof increasing pH on the rate of an e 9pfootuj ;:r: nzymatic reaction. Wha oopt: 9ur;j: ft is occurring during the phase labelled section X in the graph?
A. The substrate has all been converted to product.
B. The enzyme is saturated with substrate.
C. The active site of the enzyme has become denatured.
D. The optimum pH has been reached.
参考答案: C
本题详细解析:
The graph shows how pH affects the rate of an enzyme controlled realg ukig(3 ramsivm:- u7e)/0kction. As the pH increases, the reaction rate initially increases from 0 to reach its maximum, the optimum (Choice D) and then decreases again to 0 in the region labelled X. If the reaction rate is 0, the enzyme is no longer catalysing the reaction.
For an enzyme to catalyse a reaction, the substrate must be able to bind to the active site. If the pH shifts too far away from the optimum pH for that enzyme, bonds holding the tertiary structure together start to break, and the enzyme structure is disrupted. This leads to a change in shape of the active site, the substrate can no longer bind and the enzyme is said to be denatured.The area labelled X on the graph shows this.
The graph provides no information on how much substrate is remaining so Choice A is incorrect. To determine if the enzyme is saturated with substrate, a graph showi)igka( lusk/m37g u-v:r me i0ng substrate concentration on the x-axis and rate of reaction on the y-axis is needed. When the enzyme is saturated with substrate (Choice B) the graph plateaus , but no such graph is provided.
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