Identifying Specific Carbohydrate Structures

Sucrose is the molecule shown below(in Haworth projection).

We recognize that it's a disaccharide, and that the first molecule is -D-glucopyranose. The bond to the second monosaccharide (fructose) is tricky because the glycosidic bond is going to the anomeric carbon of fructose. Therefore, this is a 1-2 linkage. Finally, since the anomeric carbon of fructose is pointing in the same direction as the 6th carbon, this is a -D-fructopyranose.

An easy way to distinguish the substrate and the product from the enzyme is that the enzyme will end in "ase". The following are the common substrates, enzymes and the associated products.

An easy way to distinguish the substrate nd the product from the enzyme is that the enzyme will end in "ase". The following are the common substrates, enzymes and the associated products.

This ring structure is of D-glucose. The hydroxyl group on the first carbon (the carbon to the bottom right of the oxygenin the ring) can face either down (the alpha conformation) or up (the beta conformation). Note that the beta conformer is more thermodynamically stable since all the hydroxyl groups on the ring would be in the equitorial position, thus minimizing steric hinderance and intramolecular electrostatic repulsion.

The correct structures of the disaccharides are:

Maltose = glucose + glucose

Sucrose = glucose + fructose

Lactose = glucose + galactose

The structure is an aldopentose. Aldo- refers to the aldehyde at the first carbon and pentose refers to a carbohydrate with five carbons.

The structure is a ketopentose. Keto- refers to the ketone at the second carbon and pentose refers to a carbohydrate with five carbons.

Amylopectin & amylose are joined to make starch. Cellulose is found in the cell wall of plant cells. Glycogen and maltose are not found in plants.

As a pair of epimers, this means that both glucose and galactose are the same in configuration in all carbons except for one non-carbonyl carbon. To differ in the configuration of the carbonyl carbon makes an anomer not an epimer. Both glucose and galactose are aldoses.

A set of anomers will differ in the configurations of their carbonyl carbons only while a set of epimers will differ in configuration in only one carbon that is not the carbonyl carbon.