Aldohexose

Aldohexose

Aldohexoses are a class of monosaccharides that contain six carbon atoms and an aldehyde group. They are a type of hexose, which are sugars with six carbon atoms, and are important in various biological processes.

Structure

Aldohexoses have the chemical formula C₆H₁₂O₆. The presence of an aldehyde group at the first carbon atom distinguishes them from ketohexoses, which have a ketone group instead. The general structure of an aldohexose can be represented as:

H-(C=O)-(CHOH)₅-H

The carbon atoms in aldohexoses are numbered from the aldehyde group, with the aldehyde carbon being C1.

Stereochemistry

Aldohexoses have four chiral centers, which means they can exist in 2⁴ = 16 different stereoisomers. These isomers are divided into two families based on the configuration of the hydroxyl group on the fifth carbon (C5):

• D-Aldohexoses: The hydroxyl group on C5 is on the right in a Fischer projection.
• L-Aldohexoses: The hydroxyl group on C5 is on the left in a Fischer projection.

The most common naturally occurring aldohexoses are D-glucose, D-galactose, and D-mannose.

Examples of Aldohexoses

D-Glucose

D-Glucose is the most abundant aldohexose in nature and is a primary source of energy for cells. It is a key player in glycolysis and the citric acid cycle.

D-Galactose

D-Galactose is found in milk and dairy products as part of the disaccharide lactose. It is also important in the biosynthesis of glycoproteins and glycolipids.

D-Mannose

D-Mannose is less common but is found in some polysaccharides and glycoproteins. It plays a role in N-glycosylation of proteins.

Biological Importance

Aldohexoses are crucial in various metabolic pathways. They serve as building blocks for more complex carbohydrates and are involved in energy production, cell signaling, and structural functions.

Chemical Reactions

Aldohexoses can undergo several chemical reactions, including:

• Oxidation: Aldohexoses can be oxidized to form aldonic acids.
• Reduction: They can be reduced to form alditols, such as sorbitol from glucose.
• Isomerization: Aldohexoses can isomerize to form ketohexoses through an enediol intermediate.

See Also

• Monosaccharide
• Hexose
• Carbohydrate