1. Cyclic Structures of Monosaccharides
Chapter 14.3
Cyclic Structures of Monosaccharides

2. Monosaccharides in Nature
The linear form of monosaccharides is instable - only 1%
C5 and C6 carbs form Hemiacetal or cyclical form, ringform – 99%
Sugars open and close randomly, frequently
Intermolecular rearrangement

3. Hemiacetals
Glucose:
Hydroxyl group connects: C5 → C1 forming a 1,5 ether linkage.
Not a dehydration but a rearrangement!!!

4. cyclization of glucose
Cyclization of glucose B
Hayworth projection

5. Hayworth Structure of Glucose

6. C1 :non-chiral in linear form but chiral in ring: labeled α or β

7. Numbering Carbons on Hemiacetals
Always start on the right hand side
1,5 Ether Linkage

8. Cyclic Structure of Galactose
Galactose is an aldohexose that differs from glucose only with the –OH group on carbon 4
With formation of a new hydroxyl group on carbon 1 – galactose also exists in α & β forms
D-Galactose
α-Galactose
β-Galactose

9. Cyclic Structure of Fructose
Fructose is a ketohexose: C5 reacts with ketone group C2
Smaller ring: pentagon

10. Fructose Ring numbering
2,5-ether linkage

11. Chapter 14.5
Disaccharides

12. 1. Linking Monosaccharides together
Monosaccharides can react with each other to form di- and polysaccharides (only ringforms can do that!)
Dehydration Rx: involving the OH groups of two sugars, splitting out of a water molecule
Formation of an ether linkage called glycosidic bond ( in sugars only!)
Problem: which OH-groups are reacting? There are many….

13. Glycosidic bond formation

14. Naming of Glycosidic Bonds: Maltose
Carbon # of first sugar connected to Carbon # number of second sugar
Maltose: C1 is connected to C4
C1 is also in α position
Writing conventions:
α (1,4) glycosidic bond
or alpha (1-4) “

15. More examples

16. Other glycosidic bonds
beta (1-4) glycosidic bond

18. 3 Disaccharides you need to know
Maltose – malt sugar
Lactose – milk sugar
Sucrose - table sugar
Generally, a disaccharide is
characterized by….
Monosaccharide components
glycosidic bonds

19. Maltose Monomers: 1. α-D-Glucose 2.α or β-D-Glucose
Glycosidic bond: α (1-4)
Creating two chiral versions of Maltose
β Maltose α Maltose
β-D-Maltose α-D-Maltose
α/β of maltose is determined by the C1 position of second sugar

20. What’s Maltose – Malt Sugar
Obtained from the hydrolysis of starch
Used in cereals, candies, and brewing of beverages

21. Lactose Monomers: β-D-galactose with α-/β-D-glucose
Glycosidic bond: β (1-4)
Creating two chiral versions of Lactose
β-D-Lactose α-D -Lactose

22. Lactose Makes up 6-8% of human milk and 4-5% of cow’s milk
Lactose intolerance: lack of the enzyme lactase that splits disaccharide during digestion
Adult Mammals stop expressing the lactase gene – exception: many adult humans have developed a lactose tolerance (microevolution) but depends on ethnicity

23. Sucrose Monomers: α-D-glucose and β-D-fructose
Glycosidic bond: α,β (1,2)
Creating only one form
of D-Sucrose!!!

24. Sucrose
Commercial sugar, obtained from sugar beets and sugar cane

25. Warm up
1. Identify the Carb class 2. Identify the monosaccharide components 3. Identify the glycosidic bond 4. Common Name Lactulose 2 1

26. Chapter 14.6
Polysaccharides

27. Polysaccharides
A polymer of many monosaccharides joined together: glycosidic bd
Important polysaccharides:
Amylose/Amylopectin –plant starch
Glycogen – animal starch
Cellulose – plant fibers
Monomers: all D-glucose but different glycosidic bonds

28. Amylose/Amylopectin Common name starches
glucose storage in plant seeds, tubers etc
Found in grains, potatoes, beans, fruits
Soluble in water
Commercial Starch: mixture amylose 20% and amylopectin 80%

29. Amylose Monomer: α-D-glucose (about 200-4000)
Glycosidic bond: α (1,4) GB
Enzyme breaking it: Amylase
Structure: Long helical chain

30. Amylopectin Monomer: α, D-Glucose
Glycosidic Bond: α (1,4) and α (1,6) GB (every 25 glucose monomers)
Enzyme breaking it: amylase isozymes
“Branched starch”

31. Glycogen Animal starch Storage of glucose in the liver
Similar to amylopectin only more branches (every glucose molecules)

32. Cellulose Monomers: β,D-glucose Glycosidic bond: β1,4-glycosidic bonds
Enzyme breaking it: Cellulase
Insoluble in water
straight strands, found in the cell wall of plants, make plant stalks rigid and strong
Humans, animal, plants DO NOT HAVE the enzyme cellulase
only bacteria living in the guts of ruminants have cellulase

33. Cellulose
Cotton, wood

34. Digestion of Cellulose
Grazing animals and termites harbor e-coli who digest cellulose for them
In humans cellulose helps absorb toxins from digestion of proteins to maintain a healthy digestive system

35. Carbohydrates in Our Diet

36. Hydrolysis
Chemical reaction to separate polymers by inserting a water molecule