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CARBOHYDRATES
1
CARBOHYDRATES
Empirical formula: C x (H2O)y
2
CARBOHYDRATES- WHERE ARE THEY ?
In solid parts of:
 plants, up to 80%
 animals, do not exceed 2%
 In plants:
– mainly as a storage material (starch)
– building material (cellulose)
 In animals:
– source of energy
– building material:
• skeleton of invertebrates and mushrooms (chitin – protective
polysaccharide substance)
• structural function in vertebrates (glycosaminoglycans)
[ Invertebrates – animals without skeleton ]
3
CARBOHYDRATES CLASSIFICATION
 Monosaccharides – simple sugars with multiple OH groups.
Carbohydrates which cannot be decomposed to other carbohydrate
components
 Disaccharides – 2 monosaccharides covalently linked. During
hydrolysis they degrade to two monosaccharides, ex.: maltose,
saccharose
 Oligosaccharides – a few monosaccharides covalently linked;
during hydrolysis they degrade to 3 to 10 units of monosaccharides, ex.
:maltotriose
 Polysaccharides – polymers consisting of chains of monosaccharide or
disaccharide units. During hydrolysis they degrade to over 10 molecules
of monosaccharides, ex.: starch, glycogen.
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Carbohydrates - occurrence

Proteins + short chains of carbohydrates– glycoproteins

Proteins + long chains of carbohydrates – proteoglycans

glycocalyx – extracellular structure :
glycoproteins + proteoglycans + glycolipids
-
-
protects the surface of the cells against mechanical and chemical
damages
facilitates the movement of motile cells
prevents from agglomeration of cells, and from sticking to vessel walls
acts as mutual recognition sites between cells
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PHYSICAL PROPERTIES OF
MONOSACHARIDES
 COLORLESS, ODOURLESS
 USUALLY TASTE SWEET
 VERY WELL SOLUBLE IN WATER
 ROTATE THE PLANE OF POLARIZED LIGHT
 CHEMICALLY NEUTRAL (NO ACIDITY OR
BASICITY)
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MONOSACHARIDES - NOMENCLATURE
 Monosaccharides containing:
aldehyde group - are called - aldoses
ketone group - are called - ketoses
Aldoses (ex, glucose) have an
aldehyde group at one end.
H
Ketoses (ex., fructose) have a
ketone group, usually at C2.
O
C
H
C
CH2OH
OH
HO
C
H
H
C
OH
H
C
OH
CH2OH
D-glucose
C
O
HO
C
H
H
C
OH
H
C
OH
CH2OH
D-fructose
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TYPES OF MONOSACHARIDES
ISOMERISM
1.
2.
3.
4.
5.
6.
Configuration of D and L
Optical isomerism
Piranoses and furanoses
Anomers a and b
Epimers
Constitutional isomers – aldoses and ketoses
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CONFIGURATION D and L
Molecules of glyceraldehyde
are enantiomers.
Stereoisomers are isomeric molecules that have the same
molecular formula and sequence of bonded atoms (constitution),
but differ (only) in the three-dimensional orientations of their
atoms in space.
Are also called mirror images (enantiomers).
• if certain compound can be transformed to one of
glyceraldehyde isomers then this compound belongs to D or L
compounds.
• D or L does not depend on rotation of polarized light. 9
ISOMERS D and L
L-glyceraldehyde
D-glyceraldehyde
O
O
1C

1C
–H

–H
H – 2C – OH
HO – 2C – H


3CH OH
2
3CH OH
2
1CHO
L-glucose

2
HO – C – H

H – 3C – OH

HO – 4C – H

5
HO – C – H

6CH OH
2
D and L symbols determine
sugars configuration:
- hydroxyl group on the penultimate
carbon counting from aldehyde
group.
Reference is glyceraldehyde.
1CHO

H–
– OH

HO – 3C – H

H – 4C – OH

5
H – C – OH

6CH OH
2
2C
D-glucose
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TYPE L ISOMERS
L-iduronic acid
Fucose
L-fucose-1,6-N-acethyloglucosamine
a-D-fukoza
b-L-fukoza
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OPTICAL ISOMERISM OF
MONOSACHARIDES
Amount of enantiomer pairs
and diastereoisomers depends
on active centers amount.
CHO

*CHOH

*CHOH

*CHOH

*CHOH

CH2OH
For 4 centers the
amount of
enantiomers and
diastereoisomers
are 24=16
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FAMILY OF D-aldose
D-(+)- aldehyd glicerynowy
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Hemiacetal & hemiketal formation
H
An aldehyde
can react with
an alcohol to
form a
hemiacetal.
C
H
O
+
R'
OH
R'
O
R
aldehyde
C
OH
R
alcohol
hemiacetal
R
A ketone can
react with an
alcohol to form
a hemiketal.
C
R
O
+
"R
OH
R'
ketone
"R
O
C
OH
R'
alcohol
hemiketal
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Pentoses and
hexoses can form
rings, as the ketone
or aldehyde group
reacts with a distal
OH.
Glucose forms an
intra-molecular
hemiacetal, as the
C1 aldehyde group &
C5 OH group reacts,
to form a 6membered
pyranose ring,
named after pyran.
C1 is a new
asymmetric center.
1
H
2
HO
3
H
4
H
5
6
CHO
C
OH
C
H
C
OH (linear form)
C
OH
D-glucose
CH2OH
6 CH2OH
6 CH2OH
5
H
4
OH
H
OH
3
H
O
H
H
1
2
OH
OH
Alfa
DaD-glucose
α-D-glucopyranoses
glukopiranoses
5
H
4
OH
H
OH
3
H
O
OH
H
1
2
H
OH
b-D-glucose
β-D glucopyranoses
Diastereoisomers = anomers = they differ from each other with
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configuration at C1 atom only, and have different physical properties
CH2OH
1
HO
H
H
2C
O
C
H
C
OH
C
OH
3
4
5
6
HOH2C 6
CH2OH
D-fructose (linear)
H
5
H
1 CH2OH
O
4
OH
HO
2
3
OH
H
a-D-fructofuranose
Fructose forms either:
6-membered pyranose ring, in reaction of the C2 keto group with
the OH on C6, or
a 5-membered furanose ring, in reaction of the C2 keto group with
the OH on C5.
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6 CH2OH
6 CH2OH
5
H
4
OH
H
OH
3
H
O
H
H
1
2
OH
a-D-glucose
α D-glukopyranose
OH
5
H
4
OH
H
OH
3
H
O
OH
H
1
2
H
OH
D-glucose
β-Db-glucopyranose
Cyclization of glucose produces a new asymmetric center
at C1. This two stereoisomers are called anomers, a & b.
Haworth projections represent the cyclic forms of sugars
(planar rings, with the OH at the anomeric C1):
 a (OH below the ring)
 b (OH above the ring).
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H OH
4
H OH
6
H O
HO
HO
H O
HO
H
HO
5
3
H
H
2
H
OH 1
OH
a-D-glucopyranose
H
OH
OH
H
b-D-glucopyranose
Because of the tetrahedral nature of carbon bonds,
pyranose sugars actually have a "chair" or "boat"
configuration, depending on the sugar.
The above representation reflects the chair
configuration of the glucopyranose ring more
accurately than the Haworth projection.
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Mutarotation
Mutarotation is transformation of one anomeric form into another.
An intermediate form is a chain form of monosaccharide.
In D-glucose solution there is more b-D-glucopyranose.
All its –OH groups have the most energetically beneficial equatorial position.
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Monosaccharide epimers
Epimers:
Cn aldoza
epimeryczna
enediol
Cn ketoza
Cn aldoza
diastereoisomers that differ from
each other in one –OH position
– Different than at C-1 in aldose
– Different than at C-2 in ketose
– Different than at last asymmetric carbon
atom
Pair of epimers:
glucose and mannose
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Glucose epimers
D-fructose
D-glucose
D-mannose
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Chemical properties of monosaccharides
Reductive properties –only when free aldehyde or
ketone group in saccharide molecule is present.
In alkaline environment saccharides have
reductive properties and ring can be opened
In acidic environment saccharides are in cyclic
form and there is no =CO group.
Saccharides are oxidized to acids , while reduce
other substances ex.: glucose is oxidized to
gluconic acid
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Chemical properties of monosaccharides
Acid influence on saccharides – all saccharides
with more than 4 carbon atoms during heating
with strong acids are subjected to dehydration
and cyclization
Base influence on saccharides – in basic
environment reductive saccharides get enolysed
Osazone forming - saccharides with phenyl
hydrazine form yellow, insoluble in water
dihydrazones called osazones.
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Osazone formation
Epimers have the same osazone
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Sugar derivatives
CHO
COOH
CH2OH
H
H
H
C
C
C
H
C
OH
HO
C
H
OH
H
C
OH
OH
H
C
OH
H
C
OH
HO
C
H
H
C
H
C
OH
OH
OH
CH2OH
D-ribitol
CH2OH
D-gluconic acid
COOH
D-glucuronic acid
 sugar alcohol – no aldehyde or ketone group; ex., ribitol.
 sugar acid - the aldehyde group at C1, or OH at C6, is
oxidized to a carboxylic acid; ex., gluconic acid, glucuronic
acid.
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Sugar derivatives
CH2OH
CH2OH
O
H
H
OH
H
H
OH
H
OH
OH
H
NH2
a-D-glucosamine
O
H
H
H
O OH
OH
H
N
C
CH3
H
a-D-N-acetylglucosamine
amino sugar - an amino group substitutes for an
hydroxyl group. An example is glucosamine.
The amino group may be acetylated, as in
N-acetylglucosamine.
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H
O
H3C
C
O
NH
R
H
COO
H
R=
OH
H
HC
OH
HC
OH
CH2OH
OH
H
N-acetylneuraminate (sialic acid)
N-acetylneuraminate (N-acetylneuraminic acid, also called
sialic acid) is often found as a terminal residue of
oligosaccharide chains of glycoproteins.
Sialic acid imparts negative charge to glycoproteins,
because its carboxyl group tends to dissociate proton at
physiological pH, as shown here.
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Glycosidic Bonds
The anomeric hydroxyl group and a hydroxyl group of another
sugar or some other compounds can bond together, releasing water
to form a glycosidic bond:
R-OH + HO-R'  R-O-R' + H2O
ex., methanol reacts with the anomeric OH in glucose to form
methyl glucoside (methyl-glucopyranose).
H OH
H OH
H2O
H O
HO
HO
H
H
H
+
CH3-OH
H O
HO
HO
H
OH
OH
H
OH
a-D-glucopyranose
H
methanol
OCH3
methyl-a-D-glucopyranose
©
28
Glycosidic Bonds
Glycosidic anomers
©
©
29
DISACCHARIDES
Disaccharides consisting of two monosacharides,
and connected by glycosidic bond are called O-glycosides.
The most important are:
• saccharose (present in honey, fruits),
• lactose
(present in milk),
• maltose
(product of enzymatic hydrolysis of starch),
• cellobiose (product of cellulose hydrolysis).
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Disaccharides:
Maltose, a cleavage (split)
product of starch (e.g.,
amylose), is a disaccharide
with an a(1 4)
glycosidic link between C1
- C4 OH of two glucoses.
It is the a anomer (C1 O
points down).
6 CH2OH
6 CH2OH
H
5
O
H
OH
4
OH
3
H
H
H
1
H
4
4
maltose
OH
H
H
H
1
O
4
H
2
OH
OH
2OH
5
O
H
OH
H
OH
1
H
2
3
cellobiose
1
OH
H
3
H
2
H
6 CH
O
H
OH
H
OH
3
OH
5
O
O
2
6 CH2OH
H
5
H
OH
Cellobiose, a product of cellulose breakdown, b anomer (O on
C1 points up).
The b(1 4) glycosidic linkage is represented as a zig-zag, but
one glucose is actually flipped over, relative to the other.
©
31
Other disaccharides include:
 Sucrose, common table sugar, has a glycosidic bond linking the
anomeric hydroxyls of glucose & fructose.
Because the configuration at the anomeric C of glucose is an a
configuration, (O points down from ring), the linkage is a(12).
The full name of sucrose is a-D-glucopyranosyl-(12)-b-Dfructopyranose.
 Lactose, milk sugar, is composed of galactose & glucose, with
b(14) linkage from the anomeric OH of galactose.
Its full name is b-D-galactopyranosyl-(1 4)-a-D-glucopyranose.
©
32
CH2OH
H
O
H
OH
H
H
H
1
O
OH
6CH OH
2
5
O
H
4 OH
3
H
OH
H
H
H
H 1
O
H
OH
CH2OH
CH2OH
CH2OH
H
H
H
O
H
OH
H
O
O
H
H
O
H
OH
H
O
OH
2
OH
H
OH
H
OH
H
H
OH
amylose
Polysaccharides:
Plants store glucose as amylose or amylopectin,
glucose polymers, collectively called starch.
Glucose storage in polymeric form minimizes
osmotic effects.
Amylose is a glucose polymer with a(14) bonds.
The end of the polysaccharide with an anomeric C1
not involved in a glycosidic bond is called the
©
reducing end.
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CH2OH
CH2OH
O
H
H
OH
H
H
OH
H
O
OH
CH2OH
H
H
OH
H
H
OH
H
H
OH
CH2OH
O
H
OH
O
H
OH
H
H
O
O
H
OH
H
H
OH
H
H
O
4
amylopectin
H
1
O
6 CH2
5
H
OH
3
H
CH2OH
O
H
2
OH
H
H
1
O
CH2OH
O
H
4 OH
H
H
H
H
O
OH
O
H
OH
H
H
OH
H
OH
Amylopectin is a glucose polymer with mainly a(14) bonds,
but it also has branches formed by a(16) bonds. Branches
are generally longer than shown above.
The branches produce a compact structure & provide multiple
chain ends at which enzymatic cleavage can occur.
©
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CH 2OH
CH 2OH
O
H
H
OH
H
H
OH
H
O
OH
CH 2OH
H
H
OH
H
H
OH
H
H
OH
CH 2OH
O
H
OH
O
H
OH
H
H
O
O
H
OH
H
H
OH
H
H
O
4
glycogen
H
1
O
6 CH 2
5
H
OH
3
H
CH 2OH
O
H
2
OH
H
H
1
O
CH 2OH
O
H
4 OH
H
H
H
H
O
OH
O
H
OH
H
H
OH
H
OH
Glycogen, the glucose storage polymer in animals, is similar
in structure to amylopectin, but glycogen has more a(16)
branches.
The highly branched structure permits rapid glucose release
from glycogen stores, e.g., in muscle during exercise.
The ability to rapidly mobilize glucose is more essential to
animals than to plants.
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CH2OH
H
O
H
OH
H
OH
H
1
O
H
H
OH
6CH OH
2
5
O
H
4 OH
3
H
H
H 1
2
OH
O
O
H
OH
CH2OH
CH2OH
CH2OH
H
H
O
O
H
OH
H
OH
O
H
O
H
OH
H
OH
OH
H
H
H
H
H
H
H
OH
cellulose
Cellulose, a major constituent of plant cell walls, consists of long
linear chains of glucose with b(14) bonds.
Every next glucose is flipped over, due to b linkages.
This promotes forming of intra-chain and inter-chain H-bonds and
van der Waals interactions, that
cause cellulose chains to be
straight & rigid, and pack with a
crystalline arrangement in thick
bundles - microfibrils.
Schematic of arrangement of
cellulose chains in a microfibril.36
CH 2OH
D-glucuronate
6COO
H
4
6

5
H
OH
3
H
H
2
OH
1
H
H
OH
O
O
H
4
O
H
5
3
H
2
1
O
H
NH COCH
3
N-acetyl-D-glucosamine
hyaluronate
Glycosaminoglycans (mucopolysaccharides) are linear polymers of
repetitive disaccharides. Can be covalently bound to a protein to form
proteoglycans.
The constituent monosaccharides tend to be modified with: acidic groups,
amino groups, sulfated hydroxyl groups,etc.
Glycosaminoglycans tend to be negatively charged because of the
presence of acidic groups.
It is important component of connective tissues.
Some examples of glycosaminoglycan in nature include heparin as an
anticoagulant , hyaluronic acid as a component of the synovial fluid
lubricant in body joints, and chondroitins, which can be found in
connective tissues, cartilage, and tendons.
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CH 2OH
D-glucuronate
6

6COO
H
4
5
H
OH
3
H
H
2
OH
1
H
H
OH
O
O
H
4
O
H
5
3
H
2
1 O
H
NH COCH 3
N-acetyl-D-glucosamine
hyaluronate
Hyaluronate (hyaluronic acid) is a glycosaminoglycan with
a repeating disaccharide motive consisting of two glucose
derivatives, glucuronate (glucuronic acid) & N-acetylglucosamine.
The glycosidic linkages are b(13) & b(14).
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core
protein
heparan sulfate
glycosaminoglycan
transmembrane
a-helix
cytosol
Proteoglycans are glycosaminoglycans that are
covalently linked to serine residues of specific core
proteins.
The glycosaminoglycan chain is synthesized by sequential
addition of sugar residues to the core protein.
39
N-sulfo-glucosamine-6-sulfate
iduronate-2-sulfate
CH2OSO3
H
H
COO
OH
O
O
H
O
H
H
OH
H
H
H
H
OSO3
O
H
NHSO3
heparin or heparan sulfate - examples of residues
Heparan sulfate is initially synthesized on a membraneembedded core protein as a polymer of alternating
N-acetylglucosamine and glucuronate residues.
Later, in segments of the polymer, glucuronate residues may
be converted to the sulfated sugar iduronic acid, while Nacetylglucosamine residues may be deacetylated and/or
sulfated.
40
PDB 1RID
Heparin, a soluble glycosaminoglycan
found in granules of mast cells, has a
structure similar to that of heparan
sulfates, but is more highly sulfated.
When released into the blood, it inhibits
clot (coagulation) formation by interacting
with the protein antithrombin.
Heparin has an extended helical
conformation.
heparin: (IDS-SGN)5
Charge repulsion by many negatively charged groups may
contribute to this conformation.
Heparin (shown) has 10 residues, alternating IDS (iduronate-2sulfate) & SGN (N-sulfo-glucosamine-6-sulfate).
41
Proteins involved in signaling & adhesion at the cell surface
recognize & bind heparan sulfate chains.
ex., binding of some growth factors (small proteins) to cell
surface receptors is enhanced by their binding also to
heparan sulfates.
Heparan sulfate sulfatases may remove sulfate groups at
particular locations on heparan sulfate chains to alter affinity
for signal
N-sulfo-glucosamine-6-sulfate
iduronate-2-sulfate
proteins, ex.,
CH2OSO3
H
growth factors.
H
COO
OH
O
O
H
O
H
H
OH
H
H
H
©
H
OSO3
O
H
NHSO3
42
heparin or heparan sulfate - examples of residues
Glycosidic bond
C
CH2OH
Oligosaccharides
that are covalently
attached to proteins or
to membrane lipids
may have linear or
branched chains.
O
H
H
OH
O
CH2
CH
NH
H
O
serine
residue
O H
OH
H
HN
C
CH3
b-D-N-acetylglucosamine
O-linked oligosaccharide chains of glycoproteins vary in
complexity.
They bind to a protein via a glycosidic bond between a
sugar residue & a serine or threonine OH.
O-linked oligosaccharides play a role in recognition,
interaction, and enzyme regulation.
43
CH2OH
O
O
H
H
OH
HN
C
HN
CH2
C
H
H
OH
H
HN
C
CH3
O
N-acetylglucosamine
Initial sugar in N-linked
glycoprotein oligosaccharide
Asn
CH
O
HN
HC
R
C
O
X
HN
HC
R
C
O
Ser or Thr
N-linked oligosaccharides of glycoproteins tend to be
complexed and branched.
First N-acetylglucosamine is linked to a protein via the sidechain N of an asparagine residue in a particular 3-amino acid
sequence.
44
NAN
NAN
NAN
Gal
Gal
Gal
NAG
NAG
NAG
Man
Man
Man
Key:
NAG
NAG
Asn
N-linked oligosaccharide
Fuc
NAN = N-acetylneuraminate
Gal = galactose
NAG = N-acetylglucosamine
Man = mannose
Fuc = fucose
Additional monosaccharides are added, and the N-linked
oligosaccharide chain is modified by removal and addition of
residues, to yield a characteristic branched structure.
45
The End
46