Question

Name which, if any, of the following groups are not aldoseketose pairs: D-ribose and D-ribulose, D-glucose and D-fructose, D-glyceraldehyde and dihydroxyacetone.

Short answer

All given pairs are aldose-ketose pairs.

Step-by-step solution

Define Aldose and Ketose

Aldoses are monosaccharides with an aldehyde group (-CHO) as their functional group, whereas ketoses have a ketone group (C=O).

Identify the Functional Groups

Determine if each sugar is an aldose (has an aldehyde group) or a ketose (has a ketone group).

Determine for D-ribose and D-ribulose

D-ribose is an aldose (contains an aldehyde group), and D-ribulose is a ketose (contains a ketone group). This pair is an aldose-ketose pair.

Determine for D-glucose and D-fructose

D-glucose is an aldose (contains an aldehyde group), and D-fructose is a ketose (contains a ketone group). This pair is an aldose-ketose pair.

Determine for D-glyceraldehyde and dihydroxyacetone

D-glyceraldehyde is an aldose (contains an aldehyde group), and dihydroxyacetone is a ketose (contains a ketone group). This pair is also an aldose-ketose pair.

Key concepts

Monosaccharides

Monosaccharides are the simplest form of carbohydrates. They are single sugar molecules that cannot be hydrolyzed into simpler sugars. Some common monosaccharides include glucose, fructose, and ribose. Each monosaccharide is classified based on the number of carbon atoms it contains. For example, glucose and fructose are hexoses (six-carbons), while ribose is a pentose (five-carbons).
Because they are the building blocks of more complex carbohydrates, understanding monosaccharides is fundamental in biochemistry.
The general formula for monosaccharides is \((CH_2O)_n\), where 'n' can range from 3 to 7.
These sugars can exist in linear or cyclic forms, with the cyclic form being more common in biological systems.

Aldehyde Group

The aldehyde group is a functional group with the structure (-CHO). This group is characterized by a carbon atom double-bonded to an oxygen atom and single-bonded to a hydrogen atom.
Monosaccharides with an aldehyde group are called aldoses. Examples of aldoses include D-glucose and D-ribose.
In an aldose, the aldehyde group is typically found at the end of the carbon chain. This positioning makes aldoses important in various biological processes, including energy metabolism and the formation of other biomolecules.
To identify an aldose, look for the -CHO group at the terminal end of the sugar molecule.

Ketone Group

A ketone group (C=O) is a functional group where a carbon atom is double-bonded to an oxygen atom. Unlike the aldehyde group, the ketone group is found within the carbon chain, not at the end.
Monosaccharides with a ketone group are known as ketoses. Prominent examples of ketoses include D-fructose and D-ribulose.
The presence of ketone groups gives ketoses different chemical properties from aldoses. These differences are critical in various metabolic pathways.
When identifying a ketose, look for the presence of a C=O group located within the carbon skeleton of the molecule, typically the second carbon atom.