8: Carbohydrate Structures, Stereochemistry, and Glycosides


Carbohydrates, also known as sugars, are found in all living organisms. They are essential to the very source of life (ex. Ribose sugars in DNA and RNA) or sustaining life itself (ex. Metabolic conversion of carbohydrates into usable biochemical energy, ATP). Another important role of carbohydrates is structural (ex. Cellulose in plants).

• 8.1: Carbohydrates Fundamentals
The chemistry of carbohydrates most closely resembles that of alcohol, aldehyde, and ketone functional groups. As a result, the modern definition of a CARBOHYDRATE is that the compounds are polyhydroxy aldehydes or ketones. The chemistry of carbohydrates is complicated by the fact that there is a functional group (alcohol) on almost every carbon.
• 8.2: Monosaccharides
The most useful carbohydrate classification scheme divides the carbohydrates into groups according to the number of individual simple sugar units. Monosaccharides contain a single unit; disaccharides contain two sugar units; and polysaccharides contain many sugar units as in polymers - most contain glucose as the monosaccharide unit.
• 8.3: Disaccharides
The disaccharides differ from one another in their monosaccharide constituents and in the specific type of glycosidic linkage connecting them. There are three common disaccharides: maltose, lactose, and sucrose. All three are white crystalline solids at room temperature and are soluble in water.
• 8.4: Oligosaccharides
An oligosaccharide is a carbohydrate whose molecule, upon hydrolysis, yields two to ten Monosaccharid molecules. Oligosaccharides are classified into subclasses based on the number of monosaccharide molecules that form when one molecule of the oligosaccharide is hydrolyzed.
• 8.5: Polysaccharides
The most useful carbohydrate classification scheme divides the carbohydrates into groups according to the number of individual simple sugar units. Monosaccharides contain a single unit; disaccharides contain two sugar units; and polysaccharides contain many sugar units as in polymers - most contain glucose as the monosaccharide unit.
• 8.6: Exercises

Thumbnail: Ball-and-stick model of the α-D-glucose molecule, $$C_6H_{12}O_6$$. Image used with permission (Public Domain; Ben Mills).

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