MCAT Biochemistry Question 46: Answer and Explanation

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Question: 46

1. When glucose is in a straight-chain formation, it:

A. is an aldoketose.
B. is a pentose.
C. has five chiral carbons.
D. is one of a group of 16 stereoisomers.

Correct Answer: D

Explanation:

Glucose is an aldohexose, meaning that it has one aldehyde group and six carbons. Given this information, choices (A) and (B) can be eliminated. In aldose sugars, each nonterminal carbon is chiral. Therefore, glucose has four chiral centers, not five, as mentioned in choice (C). The number of stereoisomers possible for a chiral molecule is 2ⁿ, where n is the number of chiral carbons. Because glucose has four chiral centers, there are 2⁴ = 16 possible stereoisomers.

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