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Carbohydrates Lecture II Highlights

1.Linking together of more than one sugar residues creates higher order saccharides. These include disaccharides (two sugars), trisaccharides (three sugars), oligosaccharides (several sugars), and polysaccharides (many sugars).

2. Most of the linkages in higher order saccharides involve glycosidic bonds.

3. Disaccharides include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (two glucoses). Linkages of these are shown in the figures in the notes.

4. Sucrose is a non-reducing sugar (has no free anomeric hydroxyl), whereas lactose is a reducing sugar (has a single free anomeric hydroxyl). The sucrose figure in your book shows a confusing structure. You are responsible for the structure of sucrose and the linkages for the disaccharides I described in class.

5. Oligosaccharides are components of glycoproteins.

6. The most common polysaccharides include glycogen (energy storage in animals), cellulose (structural integrity in plants), starch (energy storage in plants), chitin (exoskeleton of insects).

7. Polysaccharides can be homopolymers (contain only one sugar residue) or heteropolymers (contain more than one sugar residue). Homopolymers include glycogen (glucose in alpha 1-4 linkages plus extensive alpha 1-6 branches), cellulose (glucose in beta 1-4 linkages), amylose (glucose in alpha 1-4 linkages), amylopectin (glucose in alpha 1-4 linkages plus some alpha 1-6 branches), and chitin (N-acetyl-D-glucosamine in beta 1-4 linkages).

8. Glycogen is an animal energy storage polysaccharide, amylopectin and amylose combine to form starch, which is a plant energy storage polysaccharide, cellulose is a plant structural polysaccharide, and chitin is a component of insect exoskeletons.

9. The enzyme cellulase is required to digest the beta 1-4 bonds of cellulose. Most animals do not contain cellulase. Ruminants and ungulates contain the bacterium that makes that enzyme.

10. Glycosaminoglycans are polysaccharides that contain either N-acetylgalactosamine or N-acetylglucosamine as one of their monomeric units. They are polyanionic and have interesting chemical properties, as a result. Examples include chondroitin sulfates and keratan sulfates of connective tissue, dermatan sulfates, heparin, hyaluronic acid, and others.

11. Proteoglycans are complexes of proteins and glycosaminoglycans that form feathery structures.