The monomers of polysaccharides become covalently connected by
glycosidic bonds (Figure 2-1).
|Figure 2-1 Cellobiose, the basic repeating unit of cellulose,
is a disaccharide of glucose molecules joined by b(1→4)
Carbohydrates serve several major functions in living systems.
Monosaccharides and oligosaccharides serve as readily utilizable energy
sources. Starch and glycogen act as macromolecular energy stores in
plants and animals, respectively. Carbohydrates perform structural roles,
such as cellulose in plant cell walls and chitin in the exoskeletons of
arthropods. Surface carbohydrates are often complexed with proteins as
glycoproteins or with lipids as glycolipids in the plasma membrane. The
great potential for structural diversity and thus, specificity, makes these
molecules very useful as cell-recognition markers in cellular communication
and in cell-to-cell attachments.
Glycogen consists of polymers of glucose units
joined by α(1→4) linkages and forms branched
chains by α(1→6) linkages. Starch has fewer
α(1→6) linkages than glycogen.