Part 1: Carbohydrates (continue) Prepared by: Dr A. Riasi ( Isfahan University of Technology )

2. Isfahan University of Technology Advance Biochemistry Part 1: Carbohydrates (continue) Prepared by: Dr A. Riasi ( Isfahan University of Technology) Reference: Lehninger Biochemistry

3. Polysaccharides • Polysaccharides or named glycans. • The glycans are differ from each other in: • The identity of their recurring monosaccharide units • In the length of their chains • In the types of bonds linking the units • In the degree of branching.

4. Polysaccharides

5. Polysaccharides • Homopolysaccharides are divided to two types: • Storage forms of monosaccharides: • Starch • Glycogen • Structural elements: • Cellulose • Chitin

6. Polysaccharides • Heteropolysaccharides provide extracellular support for organisms of all kingdoms. • In animal tissues, the extracellular space is occupied by several types of heteropolysaccharides.

7. Homopolysaccharides • Both storage polysaccharides (starch & glycogen) occur intracellularly as large clusters or granules.

8. Homopolysaccharides • Starch contains two types of glucose polymer: • Amylose • Amylopectin

9. Homopolysaccharides a -1,6-glycosidic bond forms at approximately every 10 glucose units, making glycogen a highly branched molecule.

10. Homopolysaccharides

11. Homopolysaccharides • Concentration of starch in different feed materials.

12. Homopolysaccharides • In vitro digestion of starch from sorghum and maize genotypes varying in the ratio amylose:amylopectin

13. Homopolysaccharides An electron micrograph of starch granules in the endosperm of sorghum showing the protein matrix with embedded protein bodies surrounding each granule. Indentations from the protein bodies can be seen on the starch granules. A scanning electron micrograph of the endosperm of barley showing starch granules of various sizes embedded in a protein matrix containing numerous protein bodies.

14. Homopolysaccharides • Glycogen is the main storage polysaccharide of animal cells. • Glycogen is a polymer of (1-4) linked subunits of glucose, with (1-6) linked branches.

15. Homopolysaccharides • It has been calculated that hepatocytes store glycogen equivalent to a glucose concentration of 0.4 M. • However, the actual concentration of glycogen, which is insoluble and contributes little to the osmolarity of the cytosol, is about 0.01 µM.

16. Homopolysaccharides • Furthermore, with an intracellular glucose concentration of 0.4 M and an external concentration of about 5 mM, the free-energy change for glucose uptake into cells against this very high concentration gradient would be prohibitively large.

17. Homopolysaccharides • Dextrans are bacterial and yeast polysaccharides made up of (α1 → 6) linked poly-D-glucose;

18. Homopolysaccharides • Synthetic dextrans are used in several commercial products for example, Sephadex.

19. Homopolysaccharides • Some homopolysaccharides serve structural roles: • Cellulose • Chitin

20. Homopolysaccharides • Cellulose is found in the cell walls of plants, particularly in: • Stalks • Stems • Trunks • All the woody portions of the plant body

21. Homopolysaccharides

22. Homopolysaccharides

23. Homopolysaccharides

24. Homopolysaccharides • Wood-rot fungi and bacteria also produce cellulase

25. Homopolysaccharides • Chitin is a linear homopolysaccharide.

26. Homopolysaccharides

27. Special polysaccharides • Some polysaccharides have special properties and found in plant cell wall: • Pectin • Hemicellulose

28. Special polysaccharides Pectin Monomer: D-galacturonic acid, L-rhamnose Others: D-galactose, D-xylose, D-arabinose short side chain) Bonding: -1,4

29. Pectin (HGA) Special polysaccharides

30. Pectin (RGI) Special polysaccharides

31. Pectin (RGII) Special polysaccharides

32. Calcium Pectate Special polysaccharides

33. Special polysaccharides

34. Special polysaccharides

35. Special polysaccharides Guar gum Monomer: galactose, mannose (galactomannan) Bonding: -1,6/-1,4

36. Special polysaccharides • The folding of polysaccharides in three dimensions follows the same principles as those governing polypeptide structure. • Because polysaccharides have so many hydroxyl groups, hydrogen bonding has an especially important influence on their structure.

37. Special polysaccharides • There is free rotation about both C-O bonds linking the residues, but as in polypeptides rotation about each bond is limited by steric hindrance by substituent.

38. Special polysaccharides

39. Special polysaccharides

40. Special polysaccharides • The most stable three-dimensional structure for starch and glycogen is a tightly coiled helix, stabilized by interchain hydrogen bonds. • Each residue along the amylose chain forms a 60 angle with the preceding residue.

41. Special polysaccharides

42. Special polysaccharides • For cellulose, the most stable conformation is that in which each chair is turned 180 relative to its neighbors, yielding a straight, extended chain. • All –OH groups are available for hydrogen bonding with neighboring chains.

43. Special polysaccharides

44. Heteropolysaccharides • Why the bacteria are not ruptured in solution with different osmotic pressures? • Heteropolysaccharides are the rigid component of bacterial cell walls. • The components are made of alternating (β1→4) linked N-acetylglucosamine and N-acetylmuramic acid residues.

45. Heteropolysaccharides

46. Heteropolysaccharides • How penicillin and related antibiotics kill bacteria?

47. Heteropolysaccharides • Agar is a sulfated heteropolysaccharides made up of D-galactose and an L-galactose derivative ether-linked between C-3 and C-6.

48. Heteropolysaccharides • Two major components of agar are: • Agarose • Agaropectin

49. Heteropolysaccharides • The extracellular matrix of animal cells is composed of an interlocking meshwork of heteropolysaccharides and fibrous proteins such as collagen, elastin, fibronectin, and laminin.

50. Heteropolysaccharides • These heteropolysaccharides are named glycosaminoglycans. • One of the two monosaccharides is always either N-acetylglucosamine or N-acetylgalactosamine. • The other is in most cases a uronic acid, usually D-glucuronic or L-iduronic acid.