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 between cells and other elements in the cellular environment

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

7. Glucose Cyclizes

8. Fructose Cyclizes

9. Ribose and Deoxyribose

10. Glycosidic Bonds

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

12. Disaccharides

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

14. 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

15. Polysaccharides

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

18. Starch
Amylose-unbranched

19. Starch
Amylopectin-branched

20. Starch A 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

22. 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

24. The glucose storage device in animals
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

25. Dextrans A 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)

27. Dextrans A 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!

28. 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

30. Cellulose

31. 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

33. 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

35. Other Structural Polysaccharides
Alginates - Ca-binding polymers in algae
Eg. CARRAGEENAN
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

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

40. 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

41. 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

42. CARBOHYDRATES
Extra carbohydrates is stored in the liver and muscle tissues as glycogen
Carbohydrates supply 4 kcal of energy per gram
“Good” and “Bad” carbohydrates
Glycemic index

43. On the “Sugarfree” Phenomenon
Saccharin
Oldest artificial sweetener
Aspartame and Acesulfame-K
Not carbohydrates
Sucralose
“Splenda”