MCAT Biochemistry Question 58: Answer and Explanation

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Question: 58

13. Galactose is the C-4 epimer of glucose, the structure of which is shown below. Which of the following structures is galactose?

  • A.
  • B.
  • C.
  • D.

Correct Answer: A

Explanation:

Galactose is a diastereomer of glucose, with the stereochemistry at C-4 (counting from the aldehyde) reversed. Being able to identify C-4 is enough to answer this question, even without looking at the glucose molecule. Because choices (B), (C), and (D) have identical stereochemistry at C-4, they are incorrect.

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