7P2-1

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Chapter 7 Outline
Monosaccharides Monosaccharide
stereoisomers Cyclic structures Reactions Examp
les and derivatives Di and oligosaccharides (We
are here.) Polysaccharides Homo and
heteropolysaccharides Glycoconjugates
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7.2 Disaccharides Sucrose

• Sucrose is formed by linking a D-glucose with b
  D-fructose to give a 1,2 glycosidic link.

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Disaccharides Lactose

• Lactose is formed by joining b D-galactose to a
  D-glucose to give a 1,4 glycoside

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Disaccharides Maltose

• Maltose is formed by linking two a-D-glucose
  molecules to give a 1,4 glycosidic link.

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DisaccharidesCellobiose

• Cellobiose is formed by linking two b D-glucose
  molecules to give a 1,4 glycosidic link. It comes
  from hydrolyzed cellulose.

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7.3 Polysaccharides Cellulose

• Cellulose is the major structural polymer in
  plants. It is a liner homopolymer composed of b
  D-glucose 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.

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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.

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Polysaccharides amylose/amylopectin
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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.

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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)
• The polymer is
• linked as
• b-1,4-units.

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Polysaccharides

• Bacterial cell walls have heteropolysaccharides
  as major components. The polymers consist of
  chains of alternating N-acetyl-b-D-glucosamine
  and N-acetylmuramic acid (next slide). The
  parallel chains are linked by short peptide
  residues.

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Polysaccharides
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Glycosaminoglycans (GAGs)

• GAGs are linear polymers with disaccharide
  repeating units. A GAG which may be familiar is
  chondroitin sulfate, a component of cartilage.

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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.

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Proteoglycans

• Proteoglycans have a very high carbohydrate to
  protein ratio, often 955, and are found in the
  extracellular matrix.
• GAG chains are linked to core proteins by N- and
  O-glycosidic links.

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Glycoproteins

• These materials contain carbohydrate residues on
  protein chains. Very important examples of these
  materials are antibodies-chemicals 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.

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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.

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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

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Glycoprotein Functions
Type E. G. Source Crb
Enzyme RNAse B Bovine 8
I G IgA Human 7
IgM Human 10
Hormone FSH Human 20
Chorionic Gn Placenta 31
Mem Prot. Glycoprotein Human RBC 60
Lectins Potato Potato 50
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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.