MCAT Question a Day

Jul 19, 2008

Passage: Oxidative stress damages cell membranes, proteins, and other cellular structures. Antioxidant defenses such as ascorbate play a key role in reducing the effects of oxidative stress. An example of antioxidant defenses is the ascorbate-glutathione cycle which helps to process H2O2 to H2O in the cell, according to the following simplified scheme:

The red couplings indicate enzymes which catalyze the oxidation of one molecule and result in the subsequent reduction of another molecule.

Question 5: The hydroxyl radical is substantially more reactive than the superoxide radical. Which of the following statements best describes the relationship between the hydroxyl radical and the superoxide radical?

(a) the hydroxyl radical has a shorter half life than the superoxide radical
(b) the hydroxyl radical has a longer half life than the superoxide radical
(c) the hydroxyl radical has a comparable half life as compared with the superoxide radical
(d) it is impossible to tell which will have the longer or shorter half life since no information is presented regarding the products of the hydroxyl radical's reaction with biological compounds

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