In terms of stereochemistry, what distinguishes alpha and beta configurations of sugars?

The alpha and beta configurations of sugars are distinguished by the configuration at the anomeric carbon. In carbohydrate chemistry, the anomeric carbon is the carbon atom that was part of the carbonyl group (aldehyde or ketone) in the open-chain form of the sugar.

When a cyclic sugar forms, the anomeric carbon becomes a chiral center, meaning it can have two different configurations based on the orientation of the hydroxyl group attached to it. In the case of an alpha configuration, the hydroxyl group on the anomeric carbon is positioned on the opposite side (down) from the CH2OH group of the sugar ring. In the beta configuration, the hydroxyl group is on the same side (up) as the CH2OH group. This distinction is crucial as it affects the properties and behaviors of the sugars in biological systems, including their reactivity and the types of glycosidic bonds they can form.

Understanding the stereochemical implications of the anomeric carbon allows for a clearer comprehension of carbohydrate structure-function relationships in biochemistry.