Identifying Specific Carbohydrate Structures - Biochemistry

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.

This is the ring/cyclic structure of D-fructose.

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

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.

Lactose is made by joining a galactose to a glucose via a carbon pathway. Both sugars are D-sugars.

D-fructose is a ketohexos. Keto indicates the ketone present on carbon 2 and hexose indicates a six-carbon sugar. The D-isomer is determined by the orientation of the highest number asymmetric carbon, which has the hydroxyl group oriented to the right in the Fischer projection.

D-galactose is an aldohexose. Aldo indicates the aldehyde at the first carbon and hexose indicates a six-carbon sugar. The D-isomer is determined by the orientation of the highest number asymmetric carbon, which has a hydroxyl group pointin to the right in this Fischer projection.

D-glucose is an aldohexose, one of the most important carbohydrates in biochemistry. Aldo indicates the aldehyde at the first carbon. Hexose indicates a six-carbon sugar. The D-isomer is determined by the orientation of the highest number asymmetric carbon, which has a hydroxyl group pointing to the right in the Fischer projection.

D-mannose is an aldohexose. Aldo indicates the aldehyde on the first carbon and the hexose indicates a six-carbon sugar. The D-isomer is determined by the orientation of the highest number asymmetric carbon, which has a hydroxyl group pointing to the right in the Fischer projection.

D-ribose is an aldopentose. Aldo indicates the aldehyde on the first carbon and the pentose indicates a five-carbon sugar. The D-isomer is determined by the orientation of the highest number asymmetric carbon, which has a hydroxyl group pointing to the right in the Fischer projection.

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.

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.

Glucose and fructose have the same constituent atoms, so they have the same molecular mass (about ). Glucose exists in aqueous solution in an equilibrium of open-chain and several cyclic isomer forms, the most common of which is pyranose, but also one of which is furanose. Upon forming a ring structure, glucose may take one of two anomers, alpha or beta. The relative proportion of the mutarotated beta form is increased versus the alpha form because the beta anomer is such that all non hydrogen substituents are in the equitorial position. Glucose can indeed be isomerized into fructose; this is part of glycolysis.

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.

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.

The beta-1,4 glycosidic bond is not a substrate for any human enzymes, and is thus left untreated.

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.