1. 1 Carbohydrates Chapter 27 Hein * Best * Pattison * Arena Colleen Kelley Chemistry Department Pima Community College © John Wiley and Sons, Inc. Version 1.0

2. 2 Chapter Outline 27.1 Carbohydrates: A First Class of Biochemicals 27.2 Classification of Carbohydrates 27.3 Importance of Carbohydrates 27.4 Monosaccharides 27.5 Structure of Glucose and Other Aldoses

3. 3 Chapter Outline (continued) 27.6 Cyclic Structure of Glucose; Mutarotation 27.7 Hemiacetals and Acetals 27.8 Structures of Galactose and Fructose 27. 9 Pentoses 27.10 Disaccharides 27.11 Structures and Properties of Disaccharides 27.12 Sweeteners and Diet 27.13 Redox Reactions of Monosaccharides 27.14 Polysaccharides Derived from Glucose

4. 4 Carbohydrates: A First Class of Biochemicals

5. 5 Carbohydrates are generally defined as polyhydroxy aldehydes or ketones or substances that yield these compounds when hydrolyzed.

6. 6 Classification of Carbohydrates

7. 7 A carbohydrate can be classified as: 1.monosaccharide 2.disaccharide 3.oligosaccharide 4.polysaccharide

8. 8 Monosaccharides A monosaccharide is a carbohydrate that cannot be hydrolyzed to simpler carbohydrate units. The monosaccharide is the basic carbohydrate unit of cellular metabolism.

9. 9 Disaccharides A disaccharide yields two monosaccharides – either alike or different – when hydrolyzed: disaccharide + water  2 monosaccharides H + or enzymes

10. 10 Monosaccharides & Disaccharides Disaccharides are often used by plants or animals to transport monosaccharides from one cell to another. The monosaccharides and disaccharides generally have the ending –ose – for example, glucose, sucrose, and lactose. These are water-soluble carbohydrates, which have a characteristically sweet taste and are called sugars.

11. 11 Oligosaccharides An oligosaccharide has two to six monosaccharide units linked together.

12. 12 Polysaccharides A polysaccharide is a macromolecular substance that can be hydrolyzed to yield many monosaccharide units: polysaccharide + water  monosaccharides H + or enzymes Polysaccharides are important structural supports, particularly in plants, and also serve as a storage depot for monosaccharides, which cells use for energy.

13. 13 Other Ways to Classify Carbohydrates As a triose, tetrose, pentose, hexose, or heptose As an aldose or ketose As a D or L isomer As a (+) or (-) isomer As a furanose or a pyranose As having an alpha (  ) or beta (  ) configuration

14. 14 Importance of Carbohydrates

15. 15 Importance of Carbohydrates 1.Carbohydrates are very effective energy-yielding nutrients. 2.Carbohydrates can serve as very effective building materials. 3.Carbohydrates are important water- soluble molecules.

16. 16MonosaccharidesMonosaccharides

17. 17 Monosaccharides The hexose monosaccharides are the most important carbohydrate sources of cellular energy. Three hexoses – glucose, galactose, and fructose – are of major significance in nutrition. –All three have the same formula, C 6 H 12 O 6, and thus deliver the same amount of cellular energy. –They differ in structure, but are biologically interconvertible.

18. 18 Glucose (dextrose) is the most important of the monosaccharides. It is an aldohexose and is found in the free state in plant and animal tissue.

19. 19 Galactose is also an aldohexose and occurs, along with glucose, in lactose and in many oligo- and polysaccharides such as pectin and gums.

20. 20 Fructose, also know as levulose, is a ketohexose that occurs in fruit juices, honey, and along with glucose, as a constituent of sucrose.

21. 21 Structures of Glucose and Other Aldoses

22. 22 Epimers Any two monosaccharides that differ only in the configuration around a single carbon atom are called epimers. D- and L-glyceraldehyde are epimers.

23. 23 Figure 27. 1 Configurations of the D-family of aldoses. The hydroxyl group on the new chiral carbon atom, added in going from triose to tetrose to pentose to hexose, is shown in red.

24. 24 Figure 27. 1 Configurations of the D-family of aldoses. The hydroxyl group on the new chiral carbon atom, added in going from triose to tetrose to pentose to hexose, is shown in red.

25. 25 Figure 27. 1 Configurations of the D-family of aldoses. The hydroxyl group on the new chiral carbon atom, added in going from triose to tetrose to pentose to hexose, is shown in red.

26. 26 Figure 27.2 An example of the Kilani-Fischer synthesis in which two aldotetrose molecules are formed from an aldotriose molecule.

27. 27 Cyclic Structure of Glucose; Mutarotation

28. 28 Figure 27.3 Mutarotation of D-glucose

29. 29 Anomers When two cyclic isomers differ only in their stereo arrangement about the carbon involved in mutarotation, they are called anomers. Mutarotation is the process by which anomers are interconverted.

30. 30 Figure 27. 4 Three-dimensional representations of the chair form of  -D-glucopyranose

31. 31 Hemiacetals and Acetals

32. 32 Cyclic structures of monosaccharides are intramolecular hemiacetals. Five- or six-membered rings are especially stable.

33. 33 Glycoside When a monosaccharide hemiacetal reacts with an alcohol, the product is an acetal. In carbohydrate terminology, this acetal structure is called a glycoside.

34. 34 Structures of Galactose and Fructose

35. 35 Galactose

36. 36 Fructose

37. 37DisaccharidesDisaccharides

38. 38 Disaccharides Disaccharides are carbohydrates composed of two monosaccharide residues united by a glycosidic linkage. sucrose + water  glucose + fructose lactose + water  galactose + glucose maltose + water  glucose + glucose H+ or sucrase H+ or lactase H+ or maltase

39. 39 Structures and Properties of Disaccharides

40. 40 Disaccharides contain an acetal structure (glycosidic linkage), and some also contain a hemiacetal structure. Maltose:

41. 41 Sweeteners and Diet

42. 42

43. 43 Redox Reactions of Monosaccharides

44. 44 Oxidation The aldehyde groups in monosaccharides can be oxidized to monocarboxylic acids by mild oxidizing agents such as bromine water.

45. 45 Reduction Monosaccharides can be reduced to their corresponding polyhydroxy alcohols by reducing agents such as H 2 /Pt or sodium amalgam, Na(Hg).

46. 46 Redox Test for Carbohydrates Under prescribed conditions, some sugars reduce silver ions to free silver, and copper (II) ions to copper (I) ions. Such sugars are called reducing sugars.

47. 47 Polysaccharides Derived from Glucose

48. 48 Starch Starch is found in plants, mainly in the seeds, roots, or tubers. Corn, wheat potatoes, rice and cassava are the chief sources of dietary starch. The two main components of starch are amylose and amylopectin. –Amylose molecules are unbranched chains composed of about 25-1300  -D-glucose units joined by  -1,4-glycosidic linkages.

49. 49 Figure 27.7 Representation of amylose.

50. 50

51. 51

52. 52 Glycogen Glycogen is the energy-storage carbohydrate of the animal kingdom. It is formed by the polymerization of glucose and is stored in the liver and in muscle tissues. Structurally, it is very similar to the amylopectin fraction of starch, except that it is more highly branched. The  -1,6-glycosidic linkages occur on one of every 12-18 glucose units.

53. 53 Cellulose Cellulose is the most abundant organic substance found in nature. It is the chief structural component of plants and wood.

54. 54 Figure 27.9 Two representations of cellulose. In the three- dimensional drawing, note the hydrogen bonding that links the extended cellulose polymers to form cellulose fibers.

55. 55