If you’re preparing for the Medical College Admission Test (MCAT), you are going to want to consult the experts. These selections from Kaplan’s MCAT Question of the Day series can help you sharpen your skills as you prepare to begin your potential journey into medical training.
The questions below come from three of the four MCAT sections—biological and biochemical foundations of living systems; chemical and physical foundations of biological systems; and psychological, social, and biological foundations of behavior. A fourth section, critical analysis and reasoning skills (commonly referred to as CARS), is based largely on inference.
Medicine can be a career that is both challenging and highly rewarding but figuring out a medical school’s prerequisites and navigating the application process can be a challenge unto itself. For students preparing for the medical school, the AMA premed glossary guide has the answers to frequently asked questions.
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Question: Which of the following is not a method by which enzymes decrease the activation energy for biological reactions?
A. Modifying the local charge environment.
B. Forming transient covalent bonds.
C. Acting as electron donors or acceptors.
D. Breaking bonds in the enzyme to provide energy.
The correct answer is D.
Kaplan explains why: Enzymes are not altered by the process of catalysis. A molecule that breaks intramolecular bonds to provide activation energy would not be able to be reused.
Question: Consider a biochemical reaction A → B, which is catalyzed by A–B dehydrogenase. Which of the following statements is true?
A. The reaction will proceed until the enzyme concentration decreases.
B. The reaction will be most favorable at 0 °C.
C. A component of the enzyme is transferred from A to B.
D. The free energy change (ΔG) of the catalyzed reaction is the same as for the uncatalyzed reaction.
The correct answer is D.
Kaplan explains why: Enzymes catalyze reactions by lowering their activation energy and are not changed or consumed during the course of the reaction. While the activation energy is lowered, the free energy of the reaction, ΔG, remains unchanged in the presence of an enzyme. A reaction will continue to occur in the presence or absence of an enzyme; it simply runs slower without the enzyme, eliminating choice (A). Most physiological reactions are optimized at body temperature, 37 °C, eliminating choice (B). Finally, dehydrogenases catalyze oxidation–reduction reactions, not transfer reactions, eliminating choice (C).
Question: While cleaning your house, you notice a large spider on the wall by your head and feel your heart rate jump up and your skin temperature grow warm. Which stage of stress response are you experiencing?
The correct answer is A.
Kaplan explains why: The initial reaction to stress, which is activation of the sympathetic nervous system, is the alarm stage of stress response.