Ease Into Prep with an MCAT^® Question of the Day

D is the correct answer.

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).