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Shuichi Nakano reported in Science in February 2000 that, "The RNA enzyme ribozyme) from hepatitis delta virus catalyzes self- cleavage of a . . . [chemical] . . . bond." This reaction is inherently slow due to the formation of an unfavorable negative charge on the ribozyme. The author goes on to show that this self- cleavage is made faster by joining it with an acid- base reaction that neutralizes the negative charge. Nakano's model describes a positively charged cytosine base on the ribozyme acting as the acid, and magnesium hydroxide acting as the base. Specifically, the cytosine donates its proton H+) to neutralize the unstable negative charge that would have formed on the ribozyme.
-What can be inferred about the free- energy profile for the self- cleavage reaction from the information provided in the paragraph?
A) It must be exothermic.
B) It must be endergonic.
C) It must be exergonic.
D) It must be endothermic.

Question

Quizplus · Accepted Answer

The fact that an acid-base reaction is necessary to speed up the self-cleavage reaction suggests that the reaction is energetically unfavorable. Therefore, the free energy profile must be in favor of the product formation, making the reaction exergonic.

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