Section 22.18 Polysaccharides 947an -1,4'-glycosidic bondan -1,6'-glycosidic bond>Figure 22.1
Branching in amylopectin. The
hexagons represent glucose units.
They are joined by -1,4 - and
a-1,6 -glyclosidic bonds.¿a ¿Amylopectin is a branched polysaccharide. Like amylose, it is composed of chains of
D-glucose units joined by linkages. Unlike amylose, however, amy-
lopectin also contains linkages. These linkages create the branches in
the polysaccharide (Figure 22.1). Amylopectin can contain up to glucose units,
making it one of the largest molecules found in nature.
Animals store their excess glucose in a polysaccharide known as glycogen. Glyco-
gen has a structure similar to that of amylopectin, but glycogen has more branches
(Figure 22.2). The branch points in glycogen occur about every 10 residues, whereas
those in amylopectin occur about every 25 residues. The high degree of branching in
glycogen has important physiological effects. When the body needs energy, many indi-
vidual glucose units can be simultaneously removed from the ends of many branches.
CH 2 OHHOOHOOCH 2 OHHOOOHOCH 2 OHHOOHOOCH 2HOOHOOOOCH 2 OHHOOHOO6 ′1five subunits of amylopectinan -1,6′-glycosidic linkage106a-1,6¿-glycosidica-1,4¿-glycosidicamylopectin glycogen>Figure 22.2
A comparison of the branching in
amylopectin and glycogen.WHY THE DENTIST IS RIGHT
Bacteria found in the mouth have an enzyme that
converts sucrose into a polysaccharide called dex-
tran. Dextran is made up of glucose units joined mainly throughand linkages. About 10% of dental
plaque is composed of dextran. This is the chemical basis of
why your dentist cautions you not to eat candy.a-1,3¿- a-1,6¿-glycosidicTutorial:
Identifying glycosidic linkages
and numbering pyranose and
furanose rings