4. Functions
• sources of energy
• intermediates in the biosynthesis of other basic
biochemical entities (fats and proteins)
• associated with other entities such as glycosides,
vitamins and antibiotics)
• form structural tissues in plants and in
microorganisms (cellulose, lignin, murein)
• participate in biological transport, cell-cell
recognition, activation of growth factors,
modulation of the immune system
6. Carbohydrates
• glucose provides energy for the brain and ½
of energy for muscles and tissues
• glycogen is stored glucose
• glucose is immediate energy
• glycogen is reserve energy
7. Carbohydrates – polyhydroxyaldehydes or polyhydroxy-ketones of
formula (CH2O)n, or compounds that can be hydrolyzed to them.
(aka sugars or saccharides)
Monosaccharides – carbohydrates that cannot be hydrolyzed to
simpler carbohydrates; eg. Glucose or fructose.
Disaccharides – carbohydrates that can be hydrolyzed into two
monosaccharide units; eg. Sucrose, which is hydrolyzed into glucose
and fructose.
Oligosaccharides – carbohydrates that can be hydrolyzed into a few
monosaccharide units.
Polysaccharides – carbohydrates that are are polymeric sugars; eg
Starch or cellulose.
Classification of carbohydrates
8. Monosaccharides - simple sugars with multiple OH
groups. Based on number of carbons (3, 4, 5, 6), a
monosaccharide is a triose, tetrose, pentose or hexose.
Disaccharides - 2 monosaccharides covalently linked.
Oligosaccharides - a few monosaccharides covalently
linked.
Polysaccharides - polymers consisting of chains of
monosaccharide or disaccharide units.
I
(CH2O)n or H - C - OH
I
Carbohydrates (glycans) have the following
basic composition:
10. Monosaccharides
• also known as simple sugars
• classified by 1. the number of carbons and 2.
whether aldoses or ketoses
• most (99%) are straight chain compounds
• D-glyceraldehyde is the simplest of the aldoses
(aldotriose)
• all other sugars have the ending ose (glucose,
galactose, ribose, lactose, etc…)
11.
12. Glucose
The chemical formula
for glucose is C6H12O6.
It is a six sided ring.
The structure on the
left is a simplified
structure of glucose
14. Monosaccharides
Aldoses (e.g., glucose) have
an aldehyde group at one end.
Ketoses (e.g., fructose) have
a keto group, usually at C2.
C
C OHH
C HHO
C OHH
C OHH
CH2OH
D-glucose
OH
C HHO
C OHH
C OHH
CH2OH
CH2OH
C O
D-fructose
15. • Compounds having same structural formula, but differ
in spatial configuration.
• Asymmetric Carbon atom:Attached to four different
atoms or groups.
• Vant Hoff’s rule: The possible isomers (2n) of a given
compound is determined by the number of asymmetric
carbon atoms (n).
• Reference C atom: Penultimate C atom, around which
mirror images are formed.
chiral centers by definition are C atoms which have
4 DIFFERENT atoms bonded to it
16. Sugar Nomenclature
For sugars with more
than one chiral center,
D or L refers to the
asymmetric C farthest
from the aldehyde or
keto group.
Most naturally occurring
sugars are D isomers.
O H O H
C C
H – C – OH HO – C – H
HO – C – H H – C – OH
H – C – OH HO – C – H
H – C – OH HO – C – H
CH2OH CH2OH
D-glucose L-glucose
17. D & L sugars are mirror
images of one another.
They have the same
name, e.g., D-glucose
& L-glucose.
Other stereoisomers
have unique names,
e.g., glucose, mannose,
galactose, etc.
The number of stereoisomers is 2n, where n is the
number of asymmetric centers.
The 6-C aldoses have 4 asymmetric centers. Thus there
are 16 stereoisomers (8 D-sugars and 8 L-sugars).
O H O H
C C
H – C – OH HO – C – H
HO – C – H H – C – OH
H – C – OH HO – C – H
H – C – OH HO – C – H
CH2OH CH2OH
D-glucose L-glucose
18. D vs L Designation
D & L designations
are based on the
configuration about
the single asymmetric
C in glyceraldehyde.
The lower
representations are
Fischer Projections.
CHO
C
CH2OH
HO H
CHO
C
CH2OH
H OH
CHO
C
CH2OH
HO H
CHO
C
CH2OH
H OH
L-glyceraldehydeD-glyceraldehyde
L-glyceraldehydeD-glyceraldehyde
19.
20. Enantiomres
A special type of isomerism is found in the pairs of structures that
are mirror images of each other. These mirror images are called
enantiomers, and the two members of the pair are designated as
a D- and an L-sugar
two monosaccharides differ in configuration around only one
specific carbon atom (with the exception of the carbonyl carbon,
see below), they are defined as epimers of each other.
21. (+)-glucose? An aldohexose
Emil Fischer (1902)
Four chiral centers, 24 = 16 stereoisomers
CHO
CH2OH
OH?
CH2CHCHCHCHCH O
OH OHOHOHOH
* * * *
22. Fructose forms either
a 6-member pyranose ring, by reaction of the C2 keto
group with the OH on C6, or
a 5-member furanose ring, by reaction of the C2 keto
group with the OH on C5.
CH2OH
C O
C HHO
C OHH
C OHH
CH2OH
HOH2C
OH
CH2OH
H
OH H
H HO
O
1
6
5
4
3
2
6
5
4 3
2
1
D-fructose (linear) -D-fructofuranose
23. Epimers – stereoisomers that differ only in configuration about
one chiral center.
CHO
OHH
HHO
OHH
OHH
CH2OH
D-glucose
CHO
HHO
HHO
OHH
OHH
CH2OH
D-mannose
epimers
Sugars are different from one
another, only in configuration
with regard to a single C atom
(other than the reference C
atom).
24. C
CH2OH
OHH
C O
H
C OHH
C
CH2OH
HOH
C O
H
C HOH
these two aldotetroses are enantiomers.
They are stereoisomers that are mirror
images of each other
C O
H
C HHO
C HHO
CH OH
C
CH2OH
OHH
C O
H
C HHO
C HHO
CHO H
C
CH2OH
OHH
these two aldohexoses are C-4 epimers.
they differ only in the position of the
hydroxyl group on one asymmetric carb
(carbon 4)
Enantiomers and epimers
25. • OPTICAL ACTIVITY
• Dextrorotatory (+) :If the sugar solution turns the
plane of polarized light to right.
. Levorotatory (–) :If the sugar solution turns the plane of
polarized light to left.
• Racemic mixture:Equimolar mixture of optical isomers
has no net rotation.
26. Hemiacetal & hemiketal formation
An aldehyde can
react with an
alcohol to form
a hemiacetal.
A ketone can
react with an
alcohol to form
a hemiketal.
O C
H
R
OH
O C
R
R'
OHC
R
R'
O
aldehyde alcohol hemiacetal
ketone alcohol hemiketal
C
H
R
O R'R' OH
"R OH "R
+
+
27. 3. Fructose (levulsoe) --- Rotation in polarimeter is left
D-Fructose b-D-Fructose -D-Fructose
CH2OH
O
CH2OH
C
HO HC
OHCH
H C
OH
O
CH2OH
C
HO HC
OHCH
H C
CH2OHCH2OH
CH
HO
H C OH
C HHO
C
OH
CH2OH
O
or
28. Anomers: Stereoisomers formed when ring is formed (, b).
C
O
CH2OH
OHCH
HO
H
HC
OH
OH
CH
HO
HO HC
OH
C H
H C OH
C H
H
HO
H C
CH2OH
O
C C
O
CH2OH
CH
HO
H
HC
OHCH
HC
OH
or
is same side with ring
29. Rules for drawing Haworth
projections
• next number the ring clockwise starting next to the
oxygen
• if the substituent is to the right in the Fisher
projection, it will be drawn down in the Haworth
projection (Down-Right Rule)
O O
1
23
4
5
1
23
4
30. Rules for drawing Haworth
projections
• draw either a six or 5-membered ring
including oxygen as one atom
• most aldohexoses are six-membered
• aldotetroses, aldopentoses, ketohexoses are
5-membered
O O
31. Pentoses and
hexoses can cyclize
as the ketone or
aldehyde reacts
with a distal OH.
Glucose forms an
intra-molecular
hemiacetal, as the
C1 aldehyde &
C5 OH react, to
form a 6-member
pyranose ring,
named after pyran.
These representations of the cyclic sugars are called
Haworth projections.
H O
OH
H
OHH
OH
CH2OH
H
OH
H H O
OH
H
OHH
OH
CH2OH
H
H
OH
-D-glucose b-D-glucose
23
4
5
6
1 1
6
5
4
3 2
H
CHO
C OH
C HHO
C OHH
C OHH
CH2OH
1
5
2
3
4
6
D-glucose
(linear form)
33. D-ribose and other five-carbon
saccharides can form either
furanose or pyranose structures
34. Cyclization of glucose produces a new asymmetric center
at C1. The 2 stereoisomers are called anomers, & b.
Haworth projections represent the cyclic sugars as having
essentially planar rings, with the OH at the anomeric C1:
(OH below the ring)
b (OH above the ring).
H O
OH
H
OHH
OH
CH2OH
H
-D-glucose
OH
H H O
OH
H
OHH
OH
CH2OH
H
H
OH
b-D-glucose
23
4
5
6
1 1
6
5
4
3 2
35. Chair and boat conformations of a pyranose sugar
2 possible chair
conformations
36. Because of the tetrahedral nature of carbon bonds,
pyranose sugars actually assume a "chair" or "boat"
configuration, depending on the sugar.
The representation above reflects the chair configuration
of the glucopyranose ring more accurately than the
Haworth projection.
O
H
HO
H
HO
H
OH
OHH
H
OH
O
H
HO
H
HO
H
H
OHH
OH
OH
-D-glucopyranose b-D-glucopyranose
1
6
5
4
3
2
37. Structural representation of sugars
• Fisher projection: straight chain
representation
• Haworth projection: simple ring in
perspective
• Conformational representation: chair and
boat configurations
44. Rules for drawing Haworth
projections
• for D-sugars the highest numbered carbon
(furthest from the carbonyl) is drawn up.
For L-sugars, it is drawn down
• for D-sugars, the OH group at the anomeric
position is drawn down for and up for b.
For L-sugars is up and b is down
45. Optical isomerism
• A property exhibited by any compound
whose mirror images are non-
superimposable
• Asymmetric compounds rotate plane
polarized light
46. POLARIMETRY
Measurement of optical activity in chiral or asymmetric
molecules using plane polarized light
Molecules may be chiral because of certain atoms or
because of chiral axes or chiral planes
Measurement uses an instrument called a polarimeter
(Lippich type)
Rotation is either (+) dextrorotatory or (-) levorotatory
47. polarimetry
Magnitude of rotation depends upon:
1. the nature of the compound
2. the length of the tube (cell or sample container) usually
expressed in decimeters (dm)
3. the wavelength of the light source employed; usually either
sodium D line at 589.3 nm or mercury vapor lamp at 546.1 nm
4. temperature of sample
5. concentration of analyte in grams per 100 ml
48. • What’s So Great About Chiral Molecules?
• • Molecules which are enantiomers of each other have
• exactly the same physical properties (melting point,
• boiling point, index of refraction, etc.) but not their
• interaction with polarized light.
• • Polarized light vibrates only in one plane; it results
• from passing light through a polarizing filter.
49.
50. []D
T
l x c
observed x 100
=
D = Na D line
T = temperature oC
obs : observed rotation in degree (specify solvent)
l = length of tube in decimeter
c = concentration in grams/100ml
[] = specific rotation
52. CHO
OHH
HHO
OHH
OHH
CH2OH
(+)-glucose
Exists only in solution. There are two
solids:
α-glucose m 146o [α] = +112.2
β-glucose m 150o [α] = +17.5
In water each mutarotates to an
equilibrium with [α] = +52.7
(63.6% β / 36.4% α)
54. Glucose oxidase
• glucose oxidase converts glucose to gluconic acid
and hydrogen peroxide
• when the reaction is performed in the presence of
peroxidase and o-dianisidine a yellow color is
formed
• this forms the basis for the measurement of
urinary and blood glucose
• Testape, Clinistix, Diastix (urinary glucose)
• Dextrostix (venous glucose)
55. Reduction
• either done catalytically (hydrogen and a catalyst)
or enzymatically
• the resultant product is a polyol or sugar alcohol
(alditol)
• glucose form sorbitol (glucitol)
• mannose forms mannitol
• fructose forms a mixture of mannitol and sorbitol
• glyceraldehyde gives glycerol
56.
57. Glycosidic Bonds
The anomeric hydroxyl and a hydroxyl of another sugar
or some other compound can join together, splitting out
water to form a glycosidic bond:
R-OH + HO-R' R-O-R' + H2O
E.g., methanol reacts with the anomeric OH on glucose
to form methyl glucoside (methyl-glucopyranose).
O
H
HO
H
HO
H
OH
OHH
H
OH
-D-glucopyranose
O
H
HO
H
HO
H
OCH3
OHH
H
OH
methyl--D-glucopyranose
CH3-OH+
methanol
H2O
60. Sugar derivatives
sugar alcohol - lacks an aldehyde or ketone; e.g., ribitol.
sugar acid - the aldehyde at C1, or OH at C6, is oxidized
to a carboxylic acid; e.g., gluconic acid, glucuronic acid.
CH2OH
C
C
C
CH2OH
H OH
H OH
H OH
D-ribitol
COOH
C
C
C
C
H OH
HO H
H OH
D-gluconic acid D-glucuronic acid
CH2OH
OHH
CHO
C
C
C
C
H OH
HO H
H OH
COOH
OHH
61. Sugar derivatives
amino sugar - an amino group substitutes for a hydroxyl.
An example is glucosamine.
The amino group may be acetylated, as in
N-acetylglucosamine.
H O
OH
H
OH
H
NH2H
OH
CH2OH
H
-D-glucosamine
H O
OH
H
OH
H
NH
OH
CH2OH
H
-D-N-acetylglucosamine
C CH3
O
H
63. Cellobiose, a product of cellulose breakdown, is the
otherwise equivalent 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.
H O
OH
H
OHH
OH
CH2OH
H
O H
OH
H
OHH
OH
CH2OH
H
O
HH
1
23
5
4
6
1
23
4
5
6
maltose
H O
OH
H
OHH
OH
CH2OH
H
O OH
H
H
OHH
OH
CH2OH
H
H
H
O1
23
4
5
6
1
23
4
5
6
cellobiose
Disaccharides:
Maltose, a cleavage
product of starch
(e.g., amylose), is a
disaccharide with an
(1 4) glycosidic
link between C1 - C4
OH of 2 glucoses.
It is the anomer
(C1 O points down).
64.
65. 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 (O points down from ring), the linkage is (12).
The full name of sucrose is -D-glucopyranosyl-(12)-
b-D-fructopyranose.)
Lactose, milk sugar, is composed of galactose &
glucose, with b(14) linkage from the anomeric OH of
galactose. Its full name is b-D-galactopyranosyl-(1 4)-
-D-glucopyranose
66. Disaccharides:
(+)-maltose “malt sugar”
two glucose units (alpha)
(+)-cellobiose
two glucose units (beta)
(+)-lactose “milk sugar”
galactose & glucose
(+)-sucrose “table sugar”
glucose & fructose
67. SUCROSE
• Cane sugar.
• α-D-glucose &β-D-fructose units held together by
(α1→β2) glycosidic bond.
• Reducing groups in both are involved in bond
formation, hence non reducing.
68. LACTOSE
Principal sugar in milk
O
OH
OH
CH2 OH
O
OH
OH
CH2 OH
O
OH
OH
β-D-galactose & β-D-glucose units held
together by β(1→4) glycosidic bond.
69. Malt sugar.
Produced during the course of digestion of
starch by the enzyme amylase.
Two α-D-glucose units held together by α(1→4)
glycosidic bond.
MALTOSE
70. • Reducing:Maltose, Lactose –with free
aldehyde or keto group.
• Non-reducing:Sucrose, Trehalose –no
free aldehyde or keto group.
72. Oligosaccharides
• Most common are the disaccharides
• Sucrose, lactose, and maltose
• Maltose hydrolyzes to 2 molecules of D-glucose
• Lactose hydrolyzes to a molecule of glucose and a
molecule of galactose
• Sucrose hydrolyzes to a moledule of glucose and a
molecule of fructose
73. 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 (14) linkages.
The end of the polysaccharide with an anomeric C1 not
involved in a glycosidic bond is called the reducing end.
H O
OH
H
OHH
OH
CH2OH
H
O H
H
OHH
OH
CH2OH
H
O
HH H O
O
H
OHH
OH
CH2OH
H
H H O
H
OHH
OH
CH2OH
H
OH
HH O
O
H
OHH
OH
CH2OH
H
O
H
1
6
5
4
3
1
2
amylose
77. Starch
• most common storage polysaccharide in
plants
• composed of 10 – 30% -amylose and 70-
90% amylopectin depending on the source
• the chains are of varying length, having
molecular weights from several thousands
to half a million
78. Polysaccharides
starch
cellulose
Starch 20% amylose (water soluble)
80% amylopectin (water insoluble)
amylose + H2O (+)-maltose
(+)-maltose + H2O (+)-glucose
starch is a poly glucose (alpha-glucoside to C-4)
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
79. Amylose and amylopectin are the 2 forms of starch. Amylopectin
is a highly branched structure, with branches occurring every 12
to 30 residues
80. Amylopectin is a glucose polymer with mainly (14)
linkages, but it also has branches formed by (16)
linkages. Branches are generally longer than shown above.
The branches produce a compact structure & provide
multiple chain ends at which enzymatic cleavage can occur.
H O
OH
H
OHH
OH
CH2OH
H
O H
H
OHH
OH
CH2OH
H
O
HH H O
O
H
OHH
OH
CH2
H
H H O
H
OHH
OH
CH2OH
H
OH
HH O
O
H
OHH
OH
CH2OH
H
O
H
O
1 4
6
H O
H
OHH
OH
CH2OH
H
H H O
H
OHH
OH
CH2OH
H
H
O
1
OH
3
4
5
2
amylopectin
81. Glycogen, the glucose storage polymer in animals, is
similar in structure to amylopectin.
But glycogen has more (16) 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.
H O
OH
H
OHH
OH
CH2OH
H
O H
H
OHH
OH
CH2OH
H
O
HH H O
O
H
OHH
OH
CH2
H
H H O
H
OHH
OH
CH2OH
H
OH
HH O
O
H
OHH
OH
CH2OH
H
O
H
O
1 4
6
H O
H
OHH
OH
CH2OH
H
H H O
H
OHH
OH
CH2OH
H
H
O
1
OH
3
4
5
2
glycogen
82. Cellulose
• Polymer of b-D-glucose attached by b(1,4) linkages
• Only digested and utilized by ruminants (cows, deers,
giraffes, camels)
• A structural polysaccharide
• Yields glucose upon complete hydrolysis
• Partial hydrolysis yields cellobiose
• Most abundant of all carbohydrates
• Cotton flax: 97-99% cellulose
• Wood: ~ 50% cellulose
• Gives no color with iodine
• Held together with lignin in woody plant tissues
83. Cellulose, a major constituent of plant cell walls, consists
of long linear chains of glucose with b(14) linkages.
Every other glucose is flipped over, due to b linkages.
This promotes intra-chain and inter-chain H-bonds and
cellulose
H O
OH
H
OHH
OH
CH2OH
H
O
H
OHH
OH
CH2OH
H
O
H H O
O H
OHH
OH
CH2OH
H
H O
H
OHH
OH
CH2OH
H
H
OHH O
O H
OHH
OH
CH2OH
H
O
H H H H
1
6
5
4
3
1
2
van der Waals interactions,
that cause cellulose chains to
be straight & rigid, and pack
with a crystalline arrangement
in thick bundles - microfibrils.
See: Botany online website;
website at Georgia Tech.
Schematic of arrangement of
cellulose chains in a microfibril.
84. Oligosaccharides
• Trisaccharide: raffinose (glucose, galactose
and fructose)
• Tetrasaccharide: stachyose (2 galactoses,
glucose and fructose)
• Pentasaccharide: verbascose (3 galactoses,
glucose and fructose)
• Hexasaccharide: ajugose (4 galactoses,
glucose and fructose)
87. Glycogen
• also known as animal starch
• stored in muscle and liver (mostly)
• present in cells as granules (high MW)
• contains both (1,4) links and (1,6) branches at
every 8 to 12 glucose unit (more frequent than in
starch)
• complete hydrolysis yields glucose
• glycogen and iodine gives a red-violet color
• hydrolyzed by both and b-amylases and by
glycogen phosphorylase
88. A portion of the structure of heparin
Heparin is a carbohydrate with anticoagulant properties. It is used in blood
banks to prevent clotting and in the prevention of blood clots in patients
recovering from serious injury or surgery
Numerous derivatives of heparin have been made (LMWH: enoxaparin
(Lovenox), dalteparin (Fragmin), tinzaparin (Innohep), fondaparinux
90. O-linked oligosaccharide chains of glycoproteins vary
in complexity.
They link to a protein via a glycosidic bond between a
sugar residue & a serine or threonine OH.
O-linked oligosaccharides have roles in recognition,
interaction, and enzyme regulation.
H O
OH
O
H
HNH
OH
CH2OH
H
C CH3
O
b-D-N-acetylglucosamine
CH2 CH
C
NH
O
H
serine
residue
Oligosaccharides
that are covalently
attached to proteins
or to membrane
lipids may be linear
or branched chains.
