MCAT Biochemistry Question 60: Answer and Explanation
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Question: 60
15. The cyclic forms of monosaccharides are:
I. hemiacetals.
II. hemiketals.
III. acetals.
- A. I only
- B. III only
- C. I and II only
- D. I, II, and III
Correct Answer: C
Explanation:
Monosaccharides can exist as hemiacetals or hemiketals, depending on whether they are aldoses or ketoses. When a monosaccharide is in its cyclic form, the anomeric carbon is attached to the oxygen in the ring and a hydroxyl group. Hence, it is only a hemiacetal or hemiketal because an acetal or ketal would require the –OH group to be converted to another –OR group.