1. Chapter 10 – Carbohydrates
Most carbohydrates are produced photo-synthetically
by bacteria, algae and plants
Carbohydrates (“hydrate of carbon”) have the empirical formula
of (CH2O)n , where n ≥ 3.
Monosaccharides: one monomeric unit
Oligosaccharides: ~2-20 monosaccharides
Polysaccharides: > 20 monosaccharides
Glycoconjugates: linkages to proteins or lipids

2. Saccharides of varying length
Aldoses and Ketoses
Trioses – three carbon sugars
Figure 8.1
Fischer projections of (a) glyceraldehyde and (b) dihydroxyacetone. The designations L (for left) and D (for right) for glyceraldehyde refer to the configuration of the hydroxyl group of the chiral carbon (C-2). Dihydroxyacetone is achiral.
Ketotriose
Aldotriose

3. Saccharides of varying length
Aldoses and Ketoses
Tetroses – 4 carbon sugars
Figure 8.3
Fischer projections of the three- to six-carbon D-aldoses. The aldoses shown in blue are the most important in our study of biochemistry.
Chiral designation comes from
the most distant chiral carbon
from the carbonyl
D-sugars dominate in nature

4. Saccharides of varying length
Aldoses and Ketoses
Figure 10.2
Pentoses – 5 carbon sugars
Hexoses – 6 carbon sugars
Chiral designation comes from
the most distant chiral carbon
from the carbonyl

5. Figure 10.1 Isomeric forms of carbohydrates

6. Epimers
Epimers – sugars that differ at only one of several chiral centers.
example: D-Mannose is an epimer of D-Glucose

7. D-fructose to form a- and b- fructofuranose
Figure 10.4 Cyclization of
D-fructose to form a- and b-
fructofuranose
anomeric carbon
Figure 8.9
Cyclization of D-ribose to form - and -D-ribopyranose and - and -D-ribofuranose.

8. Fig 10.3 Cyclization of D-glucose to form glucopyranose
Figure 8.8
Cyclization of D-glucose to form glucopyranose. The Fischer projection (top left) is redrawn as a three-dimensional representation (top right). Rotation of the bond between C-4 and C-5 brings the C-5 hydroxyl group close to the C-1 aldehyde group. Reaction of the C-5 hydroxyl group with one side of C-1 gives -D-glucopyranose; reaction of the hydroxyl group with the other side gives -D-glucopyranose. The glucopyranose products are shown as Haworth projections in which the lower edges of the ring (thick lines) project in front of the plane of the paper and the upper edges project behind the plane of the paper. In the -D anomer of glucose, the hydroxyl group at C-1 points down; in the -D anomer, it points up.
In aqueous solutions hexoses
and pentoses will cyclize
forming alpha (a) and beta (b)
forms
C1 is called the anomeric carbon

9. In aqueous solutions, it is the ring structures that dominate
These rings are NOT planar
Figure 10.5
Figure 8.10
Conformations of -D-ribofuranose. (a) Haworth projection. (b) C2’-endo envelope conformation. (c) C3’-endo envelope conformation. (d) Twist conformation. In the C2’-endo conformation, C-2 lies above the plane defined by C-1, C-3, C-4, and the ring oxygen. In the C3’-endo conformation, C-3 lies above the plane defined by C-1, C-2, C-4, and the ring oxygen. In the twist conformation shown, C-3 lies above and C-2 lies below the place defined by C-1, C-4, and the ring oxygen. The planes are shown in yellow.

10. Figure 10.7 modified monosaccharides
6-deoxy-L-galactose
Important in structural
glycans
Important in
metabolic pathways

11. Disaccharides and other Glycosides
Glycosidic bond – the primary structural linkage in all polymers
of monsaccharides
Glycosides – glucose provides the anomeric carbon
Figure 8.20
Structures of (a) maltose, (b) cellobiose, (c) lactose, and (d) sucrose. The oxygen atom of each glycosidic bond is shown in red.
Maltose is in malt and is used in brewing of beer
Cellobiose – cellulose in plants released during cellulose degradation
Figure Structures of disaccharides: maltose

12. More structures of disaccharides: lactose and sucrose
Most abundant sugar
Major carbohydrate
in milk
Sucrase, lactase and
maltase are found
on the outer surface
of the epithelial cells
lining the small
intestine.
Figure 8.20
Structures of (a) maltose, (b) cellobiose, (c) lactose, and (d) sucrose. The oxygen atom of each glycosidic bond is shown in red.
Sucrose links two anomeric carbons together
Lactose is an epimer of cellobiose
Comes from the breakdown of starch and glycogen

13. Reducing and Nonreducing ends of sugars
In linear polymeric chains of monosaccharides there
is usually one reducing end (containing the free anomeric
carbon) and one nonreducing end
Branched polysaccharides have a number of nonreducing
ends, but only one reducing end
Nonreducing end
Beta form tends to dominate.
Reducing end
(anomeric carbon)
Read Clinical Insight pg 161

14. Polysaccharides
- Homoglycans – homopolysaccharides containing only one
type of monosaccharide.
Heteroglycans – heteropolysaccharides containing residues
of more than one type of monosaccharide
The lengths and compositions of a polysaccharide may vary
within a population of these molecules
e.g.: starch and glycogen – storage polysaccharides
cellulose and chitin – structural polysaccharides
Kytin = chitin

15. Starch D-glucose is stored intracellularly in polymeric forms
- plants and fungi store glucose as starch
- Animals store glucose as glycogen
Starch is a mixture of amylose (unbranched)
and amylopectin (branched every 25 sugars)
Amylose is a linear polymer
containing only a-1,4-glycosidic
bonds.
(b) Amylopectin is a branched
polymer also contains a-1,6-bonds
Figure 10.12

16. Starch is stored by plants and used as fuel.
Prentice Hall c2002
Chapter 8

17. a-amylase on amylopectin
- a-amylase is found in plants and animals and is a hydrolase
it is an endoglycosidase – hydrolyzes internal a-(14)
glycosidic bonds

18. Glycogen is is stored by animals and used as fuel.
Prentice Hall c2002
Chapter 8

19. Glycogen Glycogen is the main storage polysaccharide of humans
Glycogen is a polysaccharide of glucose residues connected
by a-(14) linkages with a-(16) branches (one branch every
8 to 12 residues)
- Glycogen is present in large amounts in liver and skeletal muscle

20. Cellulose – a structural polysaccharide that is a
Major component of cell walls of plants
Cellulose has b-(14) glycosidic bonds
Each glucose
residue is rotated
180o relative to
the next residue
Cellulases
Pectin vs Cellulose Pectin is a water soluble polysaccharide using galacturonate-an sugar acid
Extended hydrogen bonding
between chains leads to
bundles or fibrils

21. Figure 10.14 Glycosidic bond
Determines polysaccharide
Structure.
Bent structure
Straight structure

22. - Humans digest starch and glycogens ingested in their diet
using amylases, enzymes that hydrolyze a-(14) glycosidic bond
Humans cannot hydrolyze b-(14) linkages of cellulose. Therefore
cellulose is not a fuel source for humans. It is fiber.
Certain microorganisms have cellulases, enzymes that hydrolyze
b-(14) linkages of cellulose.
- cattle have these organisms in their rumen
- termites have them in their intestinal tract

23. Carbohydrates attached to proteins form glycoproteins
Many glycoproteins are found as components of cell membranes
(chapter 11) and take part in cell adhesion and binding.
or Thr
Mucins or mucoproteins are proteins which has N-acetylgalactosamine attached. This glycoprotein is found in mucus and is a lubricant.
1st class is glycoprotein where the protein is the largest component of the sugar protein unit.
Proteoglycans-larger component is the polysaccharide
Mucins and the amino sugar
Two methods to anchor the protein to carbohydrates

24. Figure 10.15 Glycosidic bonds between proteins and carbohydrates
asparagine
serine
Thr: CH3CH(OH)-
Thr is also
used to make
O-linkages
Two methods to anchor the protein to carbohydrates

25. Figure 10.16 N-linked oligosaccharides
All N-linkages have a common core shown in grey.
Complex structure
High mannose
Fuc-fructose-methyl group on C6, Sia-sialic acid-N-aceyl glucosamine acid
Protein residue
Protein residue
Additional sugars can be attached to these cores to make diverse and unique structures

26. Proteoglycans are glycoproteins were the protein is bound to a
special class of polysaccharides called a glycosaminoglycan.
This class of glycoprotein are used as structural components and lubricants.
-In proteoglycans nearly 95% of the mass comes from the polysaccharide.
-Proteoglycans function as lubricants, structural components in tissue and mediate the adhesion of cells to the extracellular matrix.
1st class is glycoprotein where the protein is the largest component of the sugar protein unit.
Proteoglycans-larger component is the polysaccharide
Mucins and the amino sugar

27. Assignment Read Chapter 10 Read Chapter 11 Topics not covered:
Section 10.4 Lectins