MCAT Biochemistry Question 53: Answer and Explanation

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Question: 53

8. When the following straight-chain Fischer projection is converted to a chair or ring conformation, its structure will be:

  • A.
  • B.
  • C.
  • D.

Correct Answer: C

Explanation:

Start by drawing out the Haworth projection. Recall that all the groups on the right in the Fischer projection will go on the bottom of the Haworth projection, and all the groups on the left will go on the top. Next, draw the chair structure, with the oxygen in the back right corner. Label the carbons in the ring 1 through 5, starting from the oxygen and moving clockwise around the ring. Now, draw in the lines for all the axial substituents, alternating above and below the ring. Remember to start on the anomeric C-1 carbon, where the axial substituent points down. Now start filling in the substituents. The substituent can be in either position on the anomeric carbon, so skip that one for now. The –OH groups on C-2 and C-4 should point downwards while the –OH group on C-3 should point upwards; choice (C), the β-anomer of d-glucose, is the only one that matches.

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