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Carbohydrates and Glycobiology

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Title: Carbohydrates and Glycobiology


1
Chapter 7
  • Carbohydrates and Glycobiology

2
Carbohydrates are everywhere
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3
Sucrose
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es/sucrose_table_sugar_crystals.jpg
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Sucrose (table sugar)
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ition/cs348b-05/donut/fifthdonut.jpg
4
What are carbohydrates?
  • Carbo-hydrates are a group of organic compound
    that can usually represented as (CH2O)n. Glucose,
    fructose, and galactose are all carbohydrates.

a-D-Galactose
5
Classification of carbohydrate
  • carbon number
  • L- or D- isomers
  • pyranose or furanose
  • a or ß anomers
  • ketose or aldose

6
Carbon number
  • In addition to simple hexose such as glucose,
    galactose, and mannose, there are a number of
    sugar derivatives in which a hydroxyl group in
    the parent compound is replaced with another
    substituent, or carbon atom is oxidized to a
    carboxyl group.
  • Therefore, researchers must give each carbon of a
    sugar a number.

7
Carbon number
H
O
1
CH2OH
C
1
2
C
H
O
C
H
OH
2
3
C
HO
C
HO
H
H
3
4
C
C
H
OH
H
OH
4
5
H
H
C
OH
C
OH
5
6
CH2OH
CH2OH
ketose
aldose
6
8
L- and D- isomers
a25D8.7
a25D-8.7
CHO
CHO
-C-
-C-
OH
H
H
HO
CH2OH
CH2OH
-glyceraldehyde
L
-glyceraldehyde
D
9
L- and D-isomers
  • Although L- and D-isomers of glyceraldehydes are
    truly levo-rotatory (-) and dextro-rotatory (),
    L- and D- sugars are NOT. For example,
    L-arabinose a20D105.1 and D-fructose
    a20D-92

a-L-arabinose (pyranose form)
10
How to determine L- and D-
  • First, find the chiral carbon

C
H-
O

C
H-
-OH
C

-H
C
H-
OH
11
How to determine L- and D-
  • If there is more than one chiral carbon, then

H2-C-OH

H-C
O
C
O


H-C-OH
H-C-OH


H-C-OH

-H
C
HO-
H2-C-OH

L-
D-
H2-C-OH
12
Formation of the cyclic form
H
O
6
CH2OH
C
1
C
O
5
OH
H
H
C
H
OH
H
OH
C
C
1
C
HO
H
C
C
H
OH
HO
C
H
OH
H
OH
H
OH
b
a
anomer
CH2OH
13
Other sugar generate 5-member ring
CH2OH
6
C
O
HOCH2
2
O
OH
CH2OH
C
HO
H
HO
H
C
C
2
5
C
C
CH2OH
OH
C
H
OH
H
OH
H
H
OH
b
a
anomer
CH2OH
14
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20
The importance of a sialic acid
a sialic acid
Sialidase (neuraminidase)
Asialo-glycoprotein Will be removed by
asialoglycoprotein receptors in the liver
Normal protein
21
Monosaccharides
  • Colorless, crystalline solids
  • Water soluble but not soluble in nonpolar solvent
  • Taste sweet

22
Monosaccharides have reducing powers
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23
Disaccharide is made by joining two
monosaccharides
24
Lactose is only present in milk
25
Sucrose is also called table sugar
26
Trehalose is a major constituent of insect
hemolymph
27
3 ?oligosaccharide ?20
28
Polysaccharides
  • Polysaccharides can serve as fuels, structural
    elements, and extracellular support.

29
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30
Polysaccharides
  • Homopolysaccharides
  • Starch (amylose, amylopectin)
  • Glycogen
  • Chitin
  • Heteropolysaccharides
  • Peptidoglycan
  • Agar (agarose, agaropectin)
  • Glycosaminoglycans

31
Starch and glycogen are polymers of a-D-glucose
  • The main chain of starch and glycogen are
    consisted of a-D-glucose joined by (a1?4)
    glycosidic bonds.

32
The branch point of starch and glycogen (a1?6)
  • Amylopectin and glycogen have branchs.

33
Cellulose is a polymer of b-D-glucose
34
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35
amylose
cellulose
36
Chitin polymer of b-N-acetyl-D-glucosamine
GlcNAc
GlcNAc
GlcNAc
GlcNAc
37
Peptidoglycan contains heteropolysaccharides
38
Agarose is very important in molecular biology
applications
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39
Glycosaminoglycans are heteropolysaccharides
  • N-acetylglucosamine or N-acetyllgalactosamine
    uronic acid (D-glucuronic or L-iduronic acid)

40
Heparin is a natural anticoagulant
41
Glycoconjugates
  • Proteoglycans glycosaminoglycan chains
    covalently joined to a membrane or secreted
    protein
  • Glycoproteins complex oligosaccharides
    covalently joined to a protein
  • Glycolipids membrane lipids with
    oligosaccharides as hydrophilic head

42
Proteoglycans
Site of attachment
Trisaccharide bridge
Point of attachment
43
Proteoglycan aggregates
44
Glycoproteins
  • Glycoproteins are carbohydrate-protein conjugates
    in which the carbohydrate moieties are smaller
    and more structurally diverse than the
    glycosaminoglycans of proteoglycans.
  • Anomeric carbon of carbohydrate -OH of Ser/Thr
    or NH2 of Asn

45
Glycophorin A
Ser1, Gly5 ? M
  • Glycophorin A has 16 oligosaccharides covalently
    attached to it, with total 60 to 70
    monosaccharide residues.
  • It is the MN antigen of human erythrocytes.

46
O- and N-linked glycosidic linkages
47
Glycolipid and lipopolysaccharides are membrane
components
48
Glycobiology
  • Carbohydrates can be served as informational
    molecules

49
Sugar serves as aging marker of proteins
a sialic acid
Sialidase (neuraminidase)
Asialo-glycoprotein Will be removed by
asialoglycoprotein receptors in the liver
Normal protein
50
Lectins
  • Lectins are proteins that bind carbohydrates with
    high affinity and specificity.

51
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52
Membrane lectins of H. pylori binds to membrane
glycoprotein of gastric epithelial cell
Membrane lectins (P-, E- and L-selectins) play
important role in the movement of immune cells
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