7P2-1 Monosaccharides Monosaccharide stereoisomers Cyclic structures Reactions Examples and derivatives Di and oligosaccharides (We are here.) Polysaccharides Homo and heteropolysaccharides Glycoconjugates Chapter 7: Outline

7P Disaccharides: Sucrose Sucrose is formed by linking  D- glucose with  D-fructose to give a 1,2 glycosidic link. 1 2

7P2-3 Disaccharides: Lactose Lactose is formed by joining  D- galactose to  D-glucose to give a 1,4 glycoside 1  D-galactose 4  D-glucose

7P2-4 Disaccharides: Maltose Maltose is formed by linking two  -D- glucose molecules to give a 1,4 glycosidic link. 1 4

7P2-5 Disaccharides:Cellobiose Cellobiose is formed by linking two  D- glucose molecules to give a 1,4 glycosidic link. It comes from hydrolyzed cellulose. 1 4

7P Polysaccharides: Cellulose Cellulose is the major structural polymer in plants. It is a liner homopolymer composed of  D- glucose units linked  -1,4. The repeating disaccharide of cellulose is  -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.

7P2-7 Polysaccharides: Starch Starches are storage forms of glucose found in plants. They are polymers of  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.

7P2-8 Polysaccharides: amylose/amylopectin amylose Amylopectin 1,6 link at branch

7P2-9 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.

7P2-10 Polysaccharides: chitin Chitin is a linear homopolysaccharide of N-acetyl-  -D-glucosamine and provides structural support for the exoskeleton (shell) of invertibrates. (eg. Insects, lobsters, shrimp) The polymer is linked as  -1,4-units.

7P2-11 Polysaccharides Bacterial cell walls have heteropolysaccharides as major components. The polymers consist of chains of alternating N-acetyl-  -D- glucosamine and N-acetylmuramic acid (next slide). The parallel chains are linked by short peptide residues.

7P2-12 Polysaccharides

7P2-13 Glycosaminoglycans (GAGs) GAGs are linear polymers with disaccharide repeating units. A GAG which may be familiar is chondroitin sulfate, a component of cartilage.

7P Glycoconjugates Glycoconjugates are compounds that covalently link carbohydrates to proteins and lipids. Proteoglycans and glycoproteins are two kinds of glycoconjugates that contain protein.

7P2-15 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.

7P2-16 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.

7P2-17 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.

7P2-18 Glycoproteins: 3 TypeTerminal sugar AN-acetylgalactosamine B  -D-galactose ABboth the above Oneither of the above O is the “universal donor” AB is the “universal acceptor”

7P2-19 Glycoprotein Functions TypeE. G.Source% Crb EnzymeRNAse BBovine 8 I GIgAHuman 7 IgMHuman10 HormoneFSHHuman20 Chorionic GnPlacenta31 Mem Prot.GlycoproteinHuman RBC60 LectinsPotato 50

7P2-20 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.