1. Prentice Hall c2002Chapter 81 Chapter 8 - Carbohydrates Carbohydrates (“hydrate of carbon”) have empirical formulas of (CH 2 O) n, where n ≥ 3 Monosaccharides one monomeric unit Oligosaccharides ~2-20 monosaccharides Polysaccharides > 20 monosaccharides Glycoconjugates linked to proteins or lipids Trioses - 3 carbon sugars Tetroses - 4 carbon sugars Pentoses - 5 carbon sugars Hexoses - 6 carbon sugars

2. Trioses - 3 carbon sugars Fig. 8.3

3. Tetroses - 4 carbon sugars Fig. 8.3

4. Pentoses - 5 carbon sugars Fig. 8.3

5. Pentoses - 5 carbon sugars Fig. 8.3

6. Hexoses - 6 carbon sugars Fig 8.3

7. Hexoses - 6 carbon sugars Fig 8.3

8. Enantiomers and epimers D-Sugars predominate in nature Enantiomers - pairs of D-sugars and L-sugars Epimers - sugars that differ at only one of several chiral centers Example: D-galactose is an epimer of D-glucose

9. Fig 8.6 (a) Pyran and (b) furan ring systems (a) Six-membered sugar ring is a “pyranose” (b) Five-membered sugar ring is a “furanose”

10. Prentice Hall c2002Chapter 810 Fig 8.8 Cyclization of D-glucose to form glycopyranose In aqueous solution hexoses and pentoses will cyclize, forming alpha (  ) and beta (  ) forms

11. Fig 8.10 Cyclization of D-ribose to form  - and  -D-ribopyranose and  - and  -D- ribofuranose

12. 8.4 Derivatives of Monosaccharides Many sugar derivatives are found in biological systems Some are part of monosaccharides, oligosaccharides or polysaccharides These include sugar phosphates, deoxy and amino sugars, sugar alcohols and acids

13. Sugar Phosphates Fig 8.14 Some important sugar phosphates

14. Prentice Hall c2002Chapter 814 Deoxy Sugars In deoxy sugars an H replaces an OH Fig 8.15 Deoxy sugars

15. Amino Sugars An amino group replaces a monosaccharide OH Amino group is sometimes acetylated Amino sugars of glucose and galactose occur commonly in glycoconjugates

16. Sugar Alcohols (polyhydroxy alcohols) Sugar alcohols: carbonyl oxygen is reduced Fig 8.17 Several sugar alcohols

17. Sugar Acids Sugar acids are carboxylic acids Fig 8.18 Sugar acids derived from glucose

18. Prentice Hall c2002Chapter 818 Sugar Acids L-Ascorbic acid (Vitamin C) is derived from D-glucuronate Fig 8.18 L-Ascorbic acid L-Ascorbic acid (Vitamin C)

19. Disaccharides and Other Glycosides Glycosidic bond - primary structural linkage in all polymers of monosaccharides Glucosides - glucose provides the anomeric carbon Fig 8.20 Structures of disaccharides (a) maltose, (b) cellobiose

20. Fig 8.20 Structures of disaccharides (c) lactose, (d) sucrose

21. Prentice Hall c2002Chapter 821 Polysaccharides Homoglycans - homopolysaccharides containing only one type of monosaccharide Heteroglycans - heteropolysaccharides containing residues of more than one type of monosaccharide Lengths and compositions of a polysaccharide may vary within a population of these molecules

23. Prentice Hall c2002Chapter 823 Starch D-Glucose is stored intracellularly in polymeric forms Plants and fungi store glucose as starch Starch is a mixture of amylose (unbranched) and amylopectin (branched every 25 sugars) (a)Amylose is a linear polymer Figure 8.22 (a)Amylopectin is a branched polymer Figure 8.23

24. Prentice Hall c2002Chapter 824 Amylose and Amylopectin form helical structures in starch granules of plants

25. Prentice Hall c2002Chapter 825 Starch is stored by plants and used as fuel.

26. Prentice Hall c2002Chapter 826 Glycogen is is stored by animals and used as fuel.

27. Prentice Hall c2002Chapter 827 Glycogen Glycogen is the main storage polysaccharide of humans. Glycogen is a polysaccharide of glucose residues connected by  -  1-4) linkages with  -(1-6) branches (one branch per 10 sugars). Glycogen is present in large amounts in liver and skeletal muscle.

28. Cellulose, a structural polysaccharide in plants has  -(1-4) glycosidic bonds Fig 8.25 Structure of cellulose

29. Fig 8.26 Cellulose fibrils Intra- and interchain Hydrogen bonds give strength

30. Prentice Hall c2002Chapter 830 Humans digest starch and glycogen ingested in their diet using amylases, enzymes that hydrolyze  -  1-4) glycosidic bonds. Humans cannot hydrolyze  -  1-4) linkages of cellulose. Therefore cellulose is not a fuel source for humans. It is fiber. Certain microorganisms have cellulases, enzymes that hydrolyze  -  1-4) linkages of cellulose. Cattle have these organisms in their rumen. Termites have them in their intestinal tract.

31. Fig 8.27 Structure of chitin The exoskeleton of arthropods Repeating units of  -(1-4)GlcNAc residues GlcNAc = N-acetylglucosamine

32. Prentice Hall c2002Chapter 832 Glycoconjugates Heteroglycans appear in 3 types of glycoconjugates: 1. Proteoglycans 2. Peptidoglycans 3. Glycoproteins

33. Prentice Hall c2002Chapter 833 Proteoglycans Proteoglycans - glycosaminoglycan-protein complexes Glycosaminoglycans - unbranched heteroglycans of repeating disaccharides of amino sugars (D-galactosamine or D-glucosamine)

34. Fig 8.28 Repeating disaccharide of hyaluronic acid, a glycosaminoglycan GlcUA = D-glucuronate GlcNAc= N-acetylglucosamine

35. Fig 8.29 Proteoglycan aggregate of cartilage

36. Prentice Hall c2002Chapter 836 Peptidoglycans Peptidoglycans - heteroglycan chains linked to peptides Major component of bacterial cell walls Heteroglycan composed of alternating N- acetylglucosamine (GlcNAc) and N- acetylmuramic acid (MurNAc)  -(1-4) linkages connect the units

37. Fig 8.30 Glycan moiety of peptidoglycan

38. Fig 8.31 Structure of the peptidoglycan of the cell wall of Staphylococcus aureus (a) Repeating disaccharide unit, (b) Cross-linking of the peptidoglycan macromolecule

39. Penicillin inhibits a transpeptidase involved in bacterial cell wall formation Fig 8.32 Structures of penicillin and -D-Ala-D-Ala Penicillin structure resembling -D-Ala- D-Ala is shown in red

40. Glycoproteins Proteins that contain covalently-bound oligosaccharides, either to serine (O-Glycosidic linkage) or asparagine (N-glycosidic linkage) Oligosaccharide chains exhibit great variability in sugar sequence and composition Fig. 8.33 O-Glycosidic and N-glycosidic linkages

41. Fig 8.34 and 8.35. Types of glycosidic linkages