MCAT Biochemistry Question 57: Answer and Explanation

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Question: 57

12. The reaction below is an example of one step in:

  • A. aldehyde formation.
  • B. hemiketal formation.
  • C. mutarotation.
  • D. glycosidic bond cleavage.

Correct Answer: C

Explanation:

In solution, the hemiacetal ring of glucose will break open spontaneously and then re-form. When the ring is broken, bond rotation occurs between C-1 and C-2 to produce either the α- or the β-anomer. The reaction given in this question depicts the mutarotation of glucose. Choice (A) is incorrect because the reactant is an aldehyde, not the product. Choice (B) is incorrect because a hemiketal has an –OH group, an –OR group, and two –R groups. In addition, hemiketals are formed from ketones, and our starting reactant is an aldehyde. Finally, choice (D) is incorrect because there is no glycosidic bond in the starting reactant.

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