MCAT Biochemistry Question 22: Answer and Explanation
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Question: 22
7. The activity of an enzyme is measured at several different substrate concentrations, and the data are shown in the table below.
| [S] (mM) |  |
| 0.01 | 1 |
| 0.05 | 9.1 |
| 0.1 | 17 |
| 0.5 | 50 |
| 1 | 67 |
| 5 | 91 |
| 10 | 95 |
| 50 | 99 |
| 100 | 100 |
Km for this enzyme is approximately:
- A. 0.5.
- B. 1
- C. 10
- D. 50
Correct Answer: A
Explanation:
While the equations given in the text are useful, recognizing relationships is even more important. You can see that as substrate concentration increases significantly, there is only a small change in the rate. This occurs as we approach vmax. Because the vmax is near
equals
. The substrate concentration giving this rate is 0.5 mM and corresponds to Km; therefore, choice (A) is correct.