Chapter 7: Outline

1. Chapter 7: Outline Monosaccharides Monosaccharide stereoisomers Cyclic structures Reactions Examples and derivatives Di and oligosaccharides (We are here.) Polysaccharides Homo and heteropolysaccharides Glycoconjugates

2. 7.2 Disaccharides: Sucrose 2 1 • Sucrose is formed by linking a D-glucose with b D-fructose to give a 1,2 glycosidic link.

3. Disaccharides: Lactose 1 4 bD-galactose a D-glucose • Lactose is formed by joining b D-galactose to a D-glucose to give a 1,4 glycoside

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

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

6. 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.

7. 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.

8. Polysaccharides: amylose/amylopectin amylose Amylopectin 1,6 link at branch

9. 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.

10. 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.

11. 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.

12. Polysaccharides

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

14. 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.

15. 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.

16. 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.

17. 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.

18. 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”

19. Glycoprotein Functions

20. 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.