Carbohydrates

1. Carbohydrates

2. Carbohydrates • “Hydrates of carbon” (C, H, & O) • Polyhydroxy aldehydes (ALDOSES) or ketones (KETOSES) • Usually Cx(H2O)y • “Sugars” • Single unit: Monosaccharide • Two units: Disaccharide • Three units: Trisaccharide, etc. • Many units: Polysaccharide

3. Carbohydrates • Functions • Energy stores, fuels, and metabolic intermediates • Ribose and deoxyribose serve as structural framework to RNA and DNA • Structural elements in the cell walls of bacteria and plants • Linked to lipids and proteins • Mediates interactions among cells • Mediates interactions between cells and other elements in the cellular environment

4. Monosaccharides • The simplest carbohydrates; aldehydes or ketones that have two or more hydroxyl groups

5. Monosaccharides • Fischer projections of monosaccharides • D,L designation refers to the configuration of the highest-numbered asymmetric center • D,L only refers the stereocenter of interest back to D- and L-glyceraldehyde! • D,L do not specify the sign of rotation of plane-polarized light!

8. Aldehydes and Ketones Can React with Alcohols to Form Hemiacetals and Hemiketals

9. Glucose Cyclizes into a Hemiacetal

10. Fructose Cyclizes into a Hemiketal

11. Ribose and Deoxyribose

12. Conformation of Pyranose and Furanose Rings

13. Glycosidic Bonds

14. Glucopyranoside Has Different Reactivity Compared to Glucose

15. Modified Monosaccharides • Addition of substituents other than alcohols; often found on cell surfaces

16. Disaccharides

17. Polysaccharides • Energy storage and structural roles • Are homopolymers if all of the monosaccharides are the same, heteropolymers if not.

18. Some Common Polysaccharides • Starch: glucose polymer (alpha) • Potato, rice, wheat, corn • Glycogen: branched glucose polymer • Animal storage • Cellulose: glucose polymer (beta) • Plant structures, paper, cotton, wood • Chitin: Modified glucose (N-Acetyl Glucose) • Fungi cell wall, insect exoskeleton

19. Polysaccharides

20. StarchA plant storage polysaccharide • Two forms: amylose and amylopectin • Most starch is 10-30% amylose and 70-90% amylopectin • Branches in amylopectin every 12-30 residues • Amylose has alpha(1,4) links, one reducing end

22. Starch • Amylose-unbranched

23. Starch • Amylopectin-branched

24. StarchA plant storage polysaccharide • Amylose is poorly soluble in water, but forms micellar suspensions • In these suspensions, amylose is helical • iodine fits into the helices to produce a blue color

26. Why branching in Starch? Consider the phosphorylase reaction... • Phosphorylase releases glucose-1-P products from the amylose or amylopectin chains • The more branches, the more sites for phosphorylase attack • Branches provide a mechanism for quickly releasing (or storing) glucose units for (or from) metabolism

28. Glycogen The glucose storage device in animals • Glycogen constitutes up to 10% of liver mass and 1-2% of muscle mass • Glycogen is stored energy for the organism • Only difference from starch: number of branches • Alpha(1,6) branches every 8-12 residues • Like amylopectin, glycogen gives a red-violet color with iodine

29. DextransA small but significant difference from starch and glycogen • If you change the main linkages between glucose from alpha(1,4) to alpha(1,6), you get a new family of polysaccharides - dextrans • Branches can be (1,2), (1,3), or (1,4)

31. DextransA small but significant difference from starch and glycogen • Dextrans formed by bacteria are components of dental plaque • Cross-linked dextrans are used as "Sephadex" gels in column chromatography • These gels are up to 98% water!

33. Structural Polysaccharides Composition similar to storage polysaccharides, but small structural differences greatly influence properties • Cellulose is the most abundant natural polymer on earth • Cellulose is the principal strength and support of trees and plants • Cellulose can also be soft and fuzzy - in cotton

35. Cellulose

36. Structural Polysaccharides Composition similar to storage polysaccharides, but small structural differences greatly influence properties • Beta(1,4) linkages make all the difference! • Strands of cellulose form extended ribbons

38. Other Structural Polysaccharides • Chitin - exoskeletons of crustaceans, insects and spiders, and cell walls of fungi • similar to cellulose, but C-2s are N-acetyl • cellulose strands are parallel, chitins can be parallell or antiparallel

40. Other Structural Polysaccharides • Alginates - Ca-binding polymers in algae • Eg. CARAGEENAN • alternating 3-linked-α-D-galactopyranose and 4-linked-β-D-galactopyranose units • Sulfonated, uses cations to gel; Common types  • Agarose and agaropectin - galactose polymers • Glycosaminoglycans - repeating disaccharides with amino sugars and negative charges

44. Glycosaminoglycans • Made of disaccharide repeating units containing a derivative of an amino sugar, either glucosamine or galactosamine

45. Glycosaminoglycans • Present in the animal cell surface or the extracellular matrix • Usually attached to proteins to form proteoglycans • Proteoglycans resemble polysaccharides more than proteins • Function as lubricants and structural components in connective tissue, mediate adhesion of cells to the extracellular matrix, and bind factors that stimulate cell proliferation

46. Oligosaccharides are Made by Glycosyltransferases

47. Effects of Glycosyltransferases Illustrated by the ABO Blood Group http://en.wikipedia.org/wiki/Blood_type

48. Glycoproteins • Carbohydrates attached to proteins • Carbohydrates are a much smaller percentage of the weight of glycoproteins than of proteoglycans • Present in cell membranes • Cell adhesion and the binding of sperm to eggs • Present in soluble proteins

49. Linking Carbohydrates to Proteins

50. Elastase is a Soluble Glycoprotein