Carbohydrates: Structure and Classification

Study Notes

Definition: Biomolecules found abundantly in living organisms, having a wide range of functions, including providing energy, acting as energy storage molecules, forming cell membrane components, and mediating communication between cells.

Composition: Contain the elements carbon, hydrogen, and oxygen. Often written as CnH2nOn or (CH2O)n, where n > 3.
Structure: Polyhydroxy aldehydes or ketones, or compounds that yield these on hydrolysis.

Monosaccharides: Simplest form, also known as simple sugars. Cannot be hydrolyzed further. Colorless, crystalline solids soluble in water, insoluble in non-polar solvents. Possess either an aldehyde or ketone group. Classified by the number of carbon atoms (e.g., trioses, tetroses, pentoses, hexoses...).
Oligosaccharides: Compounds yielding 2 to 10 monosaccharide molecules upon hydrolysis. Monosaccharide units are joined by glycosidic linkages. Classified based on the number of monosaccharide units (e.g., disaccharides, trisaccharides...).
Polysaccharides: Contain more than 10, sometimes hundreds, of monosaccharide units. Yield more than 10 monosaccharide molecules upon hydrolysis. Differ from each other in monosaccharide identity, chain length, branching, and bond types. Important functions include structural components (e.g., cellulose, bacterial cell walls) and energy storage (e.g., glycogen, starch).

Molecular Formula: C6H12O6
Properties: Main energy source, aldohexose, glucopyranose, dextrose, reducing sugar, grape sugar.
Structure: D-Glucose and L-Glucose are stereoisomers, differing in spatial arrangement around the chiral centers.

Naming scheme: Prefix based on carbon count (e.g., tri-, tetra-, pent-), plus suffix "-ose" (e.g., triose, tetrose, pentose).

Disaccharides: Sucrose (glucose and fructose), lactose (galactose and glucose), maltose (glucose and glucose).
Trisaccharides: Raffinose, stachyose
Polysaccharides: Starch, glycogen, cellulose

Energy source: Used to fuel cellular reactions. Most abundant dietary energy source for all living beings (4 kcal/gram).
Structural components: Form protective and structural components, such as in plant cell walls (cellulose).
Intermediates: Act as metabolic intermediates. Intermediates in biosynthesis of fats and proteins.
Energy source for brain and nerve tissue.
Surface antigens and receptors: Combine with lipids and proteins to form important biomolecules like surface antigens, receptors, vitamins, and antibiotics.
Storage: Serve as storage forms, such as glycogen and starch.