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MCAT

Unit 2: Lesson 1

Foundation 1: Biomolecules

The structure of monosaccharides

Problem

Monosaccharides are the basic unit of carbohydrates, an organic class of molecules made of carbon, hydrogen, and oxygen atoms, usually in a respective ratio of 1:2:1. When in their linear chain form, these molecules are polyhydroxylated aldehydes and ketones. The name carbohydrate reflects the presence of one water molecule for every carbon atom in the general formula. Monosaccharide naming further distinguishes both the highest priority functional group and number of carbon atoms as well as the chirality of the highest numbered chiral carbon. The functional group determines the molecule’s prefix, while the suffix “ose” is applied generally to all molecules in this class of sugars. For example, a six-carbon monosaccharide with an aldehyde functional group is an aldohexose, of which glucose is a notable example. Fructose is also a six-carbon monosaccharide, however it differs from glucose in that its functional group is a ketone at carbon 2 making it a ketohexose. Lastly, the stereochemistry of the highest numbered carbon atom is distinguished as D or L. Figure 1 represents the eight possible D-aldohexoses.
What is the C-5 epimer of L-Talose?
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