Different regions of the human gut contain different protease enzymes, and the conditions in each region are not the same. Two proteases were extracted from...
Question 1 Report
Different regions of the human gut contain different protease enzymes, and the conditions in each region are not the same. Two proteases were extracted from the gut of a person: enzyme A came from the stomach and enzyme B came from the small intestine. The activity of each enzyme was then measured over a range of pH values, and the results are shown in the table. The diagram shows the parts of the gut from which the two enzymes were taken. Use the table, the diagram and your knowledge of digestion to answer the questions.
| pH | 2 | 4 | 6 | 8 | 10 |
|---|---|---|---|---|---|
| Activity of enzyme A / units | 10 | 6 | 2 | 0 | 0 |
| Activity of enzyme B / units | 0 | 1 | 5 | 9 | 4 |
(a) State the optimum pH of enzyme A and of enzyme B. [2]
(b) Name the products formed when a protease acts on a protein. [1]
(c) Using the data, suggest in which organ enzyme A acts and explain your answer. [2]
(d) Explain why enzyme A has no activity at pH 8. [2]
(e) State one region of the gut where the contents have a pH of about 8. [1]
(f) Suggest why the body produces two proteases with different optimum pH values. [1]
Answer Details
(a) Optimum pH of each enzyme [2]. The optimum pH is the pH giving the highest activity. Enzyme A is most active at pH 2 (activity 10 units), so its optimum is pH 2 [1]; enzyme B is most active at pH 8 (activity 9 units), so its optimum is pH 8 [1]. The pattern is clear when the two sets of data are plotted:
(b) Products of protein digestion [1]. Amino acids [1].
(c) Where enzyme A acts, with reason [2]. The stomach [1]; the stomach contents are acidic (about pH 2), which matches enzyme A's optimum, so this is where it is most active [1].
(d) Why enzyme A has no activity at pH 8 [2]. At pH 8 the enzyme is denatured [1]: the shape of its active site changes so the substrate can no longer fit or bind, and no reaction occurs [1].
(e) A region of the gut at about pH 8 [1]. The small intestine (duodenum) [1], which is made alkaline by bile and pancreatic juice.
(f) Why the body makes two proteases with different optima [1]. So that protein digestion can continue in regions of the gut that have different pH values [1] (acidic stomach and alkaline small intestine).
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