Covers disaccharides and polysaccharides, beginning with how glycosidic linkages join monosaccharides and how their α and β orientations affect spatial structure. It then contrasts reducing and non-reducing sugars in a comparison table, shows representative disaccharides such as maltose, cellobiose, lactose and sucrose, and reviews homopolysaccharides like starch, glycogen, cellulose, β-glucans and chitin. It closes with heteropolysaccharides (hyaluronic acid, chondroitin sulphate, pectin, heparin) and glycoprotein types and the biological significance of glycosylation.
Topic 35 of 42 in the MU Sofia syllabus for Chemistry (Dental Medicine, Year 1). The free AceMed note covers it in 7 sections, about 729 words (7 min of reading), with 20 flashcards.
In this note
Disaccharides and polysaccharides.
Spatial characteristic of glycosidic bond.
Reducing and non-reducing disaccharides.
Representative disaccharides: maltose, cellobiose, lactose and sucrose.
Homopolysaccharides: starch, glycogen, cellulose, β-glucans and chitin - structure and properties.
Heteropolysaccharides: hyaluronic acid, chondroitin sulphate, pectins and heparin - structure and properties.
Glycoproteins - types. Biological significance of glycosylation.
Disaccharides and polysaccharides.
Disaccharides:
Definition: Compounds consisting of two monosaccharide subunits bonded together by a glycosidic linkage.
Structure:
The structure involves the hemiacetal group of one monosaccharide reacting with the alcohol group of another monosaccharide.
Hemiacetal group (from one monosaccharide) interacts with the alcohol group (from another monosaccharide) to form a glycosidic linkage.
Visual Representation
Polysaccharides:
Definition: Polymers consisting of numerous monosaccharide units linked together by glycosidic bonds.
Structure:
Polysaccharides are composed of repeating units of monosaccharides linked together through glycosidic bonds.
Different polysaccharides can have varying arrangements and branching patterns.
Visual Representation:
Spatial characteristic of glycosidic bond.
Formation: Glycosidic bonds are formed readily in the presence of an acid. This occurs through a condensation reaction, where a water molecule is released as a by product. *check previous topic for more details.
Orientation: Glycosidic bonds typically form between the anomeric carbon of one monosaccharide and the hydroxyl group of another monosaccharide. The orientation of these groups determines the stereochemistry of the resulting glycosidic linkage.
Stereochemistry: The stereochemistry of the glycosidic bond can vary, leading to different structural isomers of disaccharides or polysaccharides. For example, α-glycosidic bonds have a different orientation of atoms compared to β-glycosidic bonds, resulting in distinct spatial arrangements.
Flexibility: Depending on the type of glycosidic bond (α or β) and the surrounding molecular environment, glycosidic bonds may exhibit different degrees of flexibility. This flexibility can influence the overall conformation of polysaccharides and their interactions with other molecules.
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