POLYSACCHARIDES
1. Homopolysaccharides
Starch
Glycogen
D-glucose
Cellulose
Amylose
Amylopectin
Glycogen
Cellulose
a-(1-4) D-glucose GLUCANS
a-(1-4) D-glucose, a-(1-6)
D-glucose
b-(1-4) D-glucose
HOMOPOLYSACCHARIDES
Branch point
GLYCOGEN
Non-reducing Ends
Reducing End
Glycogen is built for glucose storage and rapid
glucose release…..
Highly branched
Macromolecular
Multi ends
Cellulose is built for support. The molecules
emphasizes extended chains with close packing
b-1-4 linkage
Alternate glucose units are flipped
Digestive Enzymes
Starch Amylose
Amylases
Break internal a-1-4 bonds
a-1-4 glycosidic bond
Non Reducing
End
Will not digest Cellulose
a -glucosidase
Maltase
Maltose and maltotriose
are the major products
D-glucose units
Debranching Enzyme
Limit Dextrin
amylases
Amylopectin or Glycogen
a-1-4, a-1-6 glucosidase or Debranching enzyme
Glycogen Phosphorylase: Inserts the elements of
phosphate across the glycosidic bond-NOT Digestive
HETEROPOLYSACCHARIDES
Nature’s Lubricants
Slimy, mucous, substances
Salivary Secretions
Vitreous Humor
Joints
Synovial fluid
GLYCOSAMINOGLYCANS (GAGS)
Chondroitin Sulfate
Hyaluronic Acid
Keratan Sulfate
Dermatin Sulfate
Heparin
Repeating unit is a Negatively
charged disaccharide
Heteropolysaccharides
Amino Sugars
CH2OH
O
NH
Amine group on
carbon 2
Acetyl group on
amine
C=O
CH3
Amino sugars are always acetylated
HETEROPOLYSACCHARIDES
Uronic Acids
Sulfate Sugars
CH2OSO3=
O
COO
Negative
Charge
O
NH
C=O
CH3
D-glucuronic acid
(GlcUA)
N-acetylgalactosamine6-sulfate (GalNac-6s)
b 1-3
b 1-4
CH2OSO3=
COO
O
CH2OSO3=
O
O
O
NH
C=O
CH3
Repeating unit of
CHONDROITIN 6 SULFATE
COO
O
O
O
NH
C=O
CH3
Repeating
disaccharide
Proteoglycans
proteins with
one or more covalently linked
GAG chains
Link Protein
Core protein
GAG
Hyaluronate
GLYCOPROTEINS
CH2OH
O
NH
C=O
CH2
C
N
Protein is the Major component
N
C
O
Asparagine linkage
Sia
Sia
Gal
Gal
GlcNAc
GlcNAc
Man
Man
Man
Typical
Oligosaccharide
Chain in a
Glycoprotein
GlcNAc
GlcNAc
Asn
Bi-Antennary
Carbohydrates in Proteins are Information Molecules
Diversity allows recognition patterns to vary:
a or b configuration on C-1
Linking -OH groups on different positions
Types of sugars and presence or absence of branching
Presence or absence of sialic acid
Patterns guide biological processes
Carbohydrate-binding proteins (lectins) recognize specific patterns
or features and interact with specific sites on
oligosaccharide chains
Carbohydrate-binding Proteins (lectins)
Recognize oligosaccharide chains on cell membranes
Examples:
Plant lectins:
concanavalin A (a-mannose residues)
wheat germ agglutinin (GlcNAc-GlcNAc-GlcNac)
peanut lectin (Gal (b1-3)-GalNac)
[Physiological role uncertain; binding of rhizobium bacteria
to root hairs for nitrogen fixation is one function].
Asialoglycoprotein Receptor on surface of liver cells:
Allows liver to remove old proteins that have lost
their sialic acid from the circulation
Exposed galactose residue is the signal for removal
Mannose-6-Phosphate Receptor: Targets proteins for
destruction in the lysosomes
ZP3 Receptor on surface of sperm:
ZP3 glycoprotein in extracellular coat of ovulated eggs
a-linked galactose at the non-reducing end
Binding triggers release of sperm enzymes, dissolves
zona pellucida to allow sperm to enter
Selectins: (Carbohydrate-binding adhesive proteins)
Surface of neutrophils, lymphocytes, leukocytes
Interacts with carbohydrates on endothelial cells,
lymph-node vessels and platelets
E-selectins recognize injured endothelial cells
Binds lymphocytes to endothelial cells in order
to penetrate into underlying cell layer
Creates and perpetuates an inflammatory condition
L-selectins allow circulating lymphocytes to return to sites
in lymph nodes from which they were derived…
return is called homing
Binding mediated by Ca2+
Prevented by removal of sialic acid