Carbohydrates

1. Carbohydrates

2. Structure of Carbohydrates

3. Properties of Carbohydrates • Most abundant class of organic molecules • Source: Photosynthesis • Classification • Monosaccharides • Stereoisomers • Aldehydes (Aldose) or Ketones (Ketose) • Number of Carbons (ie 3=triose; 6=hexose) • Combined: Aldotriose/Ketotetrose • Polymers • Oligosaccharides (2- ~20 sugars) • Polysaccharides (> ~20 sugars)

4. Biological Roles of Carbohydrates • Energy source • Energy storage • Cell walls • Recognition events • Between proteins (targeting) • Between cells • Signalling • Components of other biological molecules • Antibiotics • Enzyme cofactors • Nucleic Acids

5. Monosaccharides(Sugars)

6. Classes of Monosaccharides

7. Chirality D- versus L- determined by chirality of highest number carbon (from aldehyde or ketone)

8. Aldoses Figure 8-1

9. Aldoses Figure 8-1

10. Ketoses Figure 8-2

11. Ketoses Figure 8-2

12. Epimers(stereoisomers differing by configuration of only one of several chiral centers)

13. Epimers(stereoisomers differing by configuration of only one of several chiral centers)

14. Enantiomers(mirror images)

15. Mutarotation Creation of new chiral center

16. Formation of Hemiacetal

17. Formation of Hemketal

18. Anomeric Carbon Atom Mutarotation Reversible Creation of new asymmetric center

19. Cyclization of D-Glucose

20. Anomers • Anomeric carbon atom • Most oxidized carbon atom • Shares electrons with 2 oxygen atoms • -configuration has -OH on opposite side of ring from CH2OH group at chiral center that designates D- or L-

21. Cyclization of D-Fructose(biologically relevant forms)

22. Nomenclature

23. Examples of Nomenclature Configuration of anomeric carbon -D-glucopyranose -D-fructofuranose Anomeric carbon modification: ose: reducing oside: non-reducing Configuration of sugar Sugar prefix Ring Type *not required

24. Cyclization of D-Fructose(biologically relevant forms)

25. Chair Conformations of -D-glucopyranose Equatorial Axial Chair and Boat Forms Equitorial and Axial Substituents Steric Crowding: equitorial more stable Figure 8-5

26. Derivatives of Monosaccharides

27. Phosphate Esters

28. Deoxy Sugars Note: 5-membered ring form is used in biological systems

29. Amino Sugars(e.g. GlcNAc-6-P)

30. Sugar Alcohols

31. Glycosides

32. Structure of Glycosides

33. Glycosidic Linkages (glycoside) Acetal Stable: no mutarotation Non-reducing sugar (no free anomeric C atom)

34. Nomenclature

35. Reducing test • Free Aldehydes are reductants • If free to mutarotate sugar is a reductant • Must have only –OH at anomeric carbon Cu2O Cupric oxide brick-red precipitate

36. Disaccharides

37. Sucrose (non-reducing) OR: Glc(α1 β2)Fru

38. Sucrose OR: Glc(α1 β2)Fru

39. -Maltose Glc(α14)Glc

40. -Lactose Gal(β14)Glc

41. Nomenclature • Recognize individual monosaccharides • Drop the –se and add root for rings • 6 member: pyran • 5 member: furan • Attach: • ose: can mutarotate • oside: canNOT mutarotate • osyl: not terminal residue • Indicate carbon to carbon number linkage (##) • Label each residue with D or L and α or β

42. Oligosaccharides • Generally complex • Heteropolymers • Branched • Various Cellular Functions • Receptors • Antigens • Signal transduction • Trafficking

43. O-linked Oligosaccharides(serine/threonine)

44. N-linked Oligosaccharides(asparagine)

45. Sugar groups on glycoproteins frequently function in recognition

46. Polysaccharides • Simpler structures • Homopolymers • Less branching • Limited Cellular Functions • Structural/Protective • Energy Storage

47. Linear Polysaccharides

48. Branched Polysaccharides

49. Functions of Polysaccharides • Structural - e.g. plant cell walls, cement between cells (animals): • -linkages stable to enzymatic cleavage • Storage - e.g. glycogen as energy reserves: • -linkages are readily cleaved • Potential osmotic problem • Accessibility for energy production • -linkages • Branching

50. Cellulose(plant cell walls)