Chapter 7: Outline
Monosaccharides
Monosaccharide stereoisomers
Cyclic structures
Reactions
Examples and derivatives
Di and oligosaccharides (We are here.)
Polysaccharides
Homo and heteropolysaccharides
Glycoconjugates
7P2-1
7.2 Disaccharides: Sucrose
Sucrose is formed by linking a Dglucose with b D-fructose to give a 1,2
glycosidic link.
CH2OH
H
H
OH
O H HO CH2
H
HO
H
2
1
OH
O
H
O
H
OH
HO
CH2OH
H
7P2-2
Disaccharides: Lactose
Lactose is formed by joining b Dgalactose to a D-glucose to give a 1,4
glycoside
CH2OH
HO
H
CH2OH
O
H
OH
H
H
OH
b D-galactose
O H
H
1
O
H
H
4
OH
H
H
OH
OH
a D-glucose
7P2-3
Disaccharides: Maltose
Maltose is formed by linking two a-Dglucose molecules to give a 1,4
glycosidic link.
CH2OH
CH2OH
H
HO
H
OH
H
O H
H
H
1
OH
O
4
O H
H
OH
H
H
OH
OH
4-O-a-D-glucopyranosyl-a-D-glucopyranose
7P2-4
Disaccharides:Cellobiose
Cellobiose is formed by linking two b Dglucose molecules to give a 1,4
glycosidic link. It comes from
hydrolyzed cellulose.
CH2OH
H
HO
CH2OH
O
O
H
H
OH
H
H
OH
1
O
H
4
OH
H
OH
H
H
OH
H
4-O-b-D-glucopyranosyl-b-D-glucopyranose
7P2-5
7.3 Polysaccharides: Cellulose
Cellulose is the major structural
polymer in plants. It is a liner
homopolymer composed of b Dglucose units linked b-1,4. The
repeating disaccharide of cellulose
is b-cellobiose.
Animals lack the enzymes
necessary to hydrolyze cellulose.
The bacteria in ruminants (eg.
cows) can digest cellulose so that
they can eat grass, etc.
7P2-6
Polysaccharides: Starch
Starches are storage forms of glucose
found in plants.
They are polymers of a linked glucose.
If the links are only 1,4, the polymer is
linear and is called amylose. (Figure
on next slide.) Amylose usually
assumes a helical configuration with
six glucose units per turn.
If the links are both 1,4 and 1,6, the
polymer is branched and is called
amylopectin. (Figure on next slide.
7P2-7
Polysaccharides: amylose/amylopectin
H
O
H
OH
H
O H
H
H
O
OH
O
H
OH
O H
H
H
O
O
H
OH
H
OH
OH
H
O H
H
H
O
OH
O H
H
OH
H
O
H
OH
H
H
OH
O
CH2OH
CH2
O H
H
H
OH
Amylopectin
1,6 link at branch
H
H
OH
O H
amylose
H
OH
CH2OH
O H
H
H
O
H
OH
O
H
OH
CH2OH
H
H
H
CH2OH
CH2OH
H
O H
H
OH
CH2OH
CH2OH
CH2OH
CH2OH
H
O
H
OH
H
O H
H
OH
H
O
O H
H
OH
H
H
OH
O
7P2-8
Polysaccharides: glycogen
The storage carbohydrate in animals
is glycogen. It is a branched chain
polymer like amylopectin but it has
more frequent branching (about
every 10 residues). Glycogen is
stored in liver and muscle cells.
7P2-9
Polysaccharides: chitin
Chitin is a linear homopolysaccharide of
N-acetyl-b-D-glucosamine and provides
structural support for the exoskeleton
(shell) of invertibrates. (eg. Insects,
lobsters, shrimp)
CH2OH
The polymer is
O OH
H
linked as
H
b-1,4-units.
OH H
HO
H
H HN C CH3
O
7P2-10
Polysaccharides
Bacterial cell walls have
heteropolysaccharides as major
components. The polymers consist of
chains of alternating N-acetyl-b-Dglucosamine and N-acetylmuramic acid
(next slide). The parallel chains are
linked by short peptide residues.
7P2-11
Polysaccharides
CH2OH
O OH
H
H
O
H
HO
H
CH3CH H HN C CH3
O
COO
N-acetyl muramic acid
7P2-12
Glycosaminoglycans (GAGs)
GAGs are linear polymers with
disaccharide repeating units. A GAG
which may be familiar is chondroitin
sulfate, a component of cartilage.
COOH
O
CH2OSO3H
O
HO
OH
O
O
OH
HN C CH3
O
7P2-13
7.4 Glycoconjugates
Glycoconjugates are compounds
that covalently link carbohydrates
to proteins and lipids.
Proteoglycans and glycoproteins are
two kinds of glycoconjugates that
contain protein.
7P2-14
Proteoglycans
Proteoglycans have a very high
carbohydrate to protein ratio, often
95:5, and are found in the
extracellular matrix.
GAG chains are linked to core
proteins by N- and O-glycosidic
links.
7P2-15
Glycoproteins
These materials contain
carbohydrate residues on protein
chains. Very important examples
of these materials are antibodieschemicals which bind to antigens
and immobilize them.
The carbohydrate part of the
glycoprotein plays a role in
determining the part of the antigen
molecule to which the antibody
binds.
7P2-16
Glycoproteins: 2
The human blood groups A, B, AB,
and O depend on the
oligosaccharide part of the
glycoprotein on the surface of
erythrocyte cells. The terminal
monosaccharide of the
glycoprotein at the nonreducing
end determines blood group.
7P2-17
Glycoproteins: 3
Type
Terminal sugar
A
N-acetylgalactosamine
B
a-D-galactose
AB
both the above
O
neither of the above
O is the “universal donor”
AB is the “universal acceptor”
7P2-18
Glycoprotein Functions
Type
Enzyme
IG
E. G.
RNAse B
IgA
IgM
Hormone FSH
Chorionic Gn
Mem Prot. Glycoprotein
Lectins
Potato
Source
Bovine
Human
Human
Human
Placenta
Human RBC
Potato
%
Crb
8
7
10
20
31
60
50
7P2-19
Glycoprotein Functions: Recognition
Cell-molecule
Insulin receptor
Cell-virus
Gp120 is the target binding site for HIV
Cell-cell
Play a role in glycocalyx (cell coat)
adhesion between cells.
7P2-20