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OPTOM FASLU MUHAMMED
Carbohydrates are compounds of great importance in both the biological and
commercial world
They are used as a source of energy in all organisms and as structural materials in
membranes, cell walls and the exoskeletons of many arthropods
All carbohydrates contain the elements carbon (C), hydrogen (H) and oxygen (O)
with the hydrogen and oxygen being present in a 2 : 1 ratio
THE GENERAL FORMULA OF A CARBOHYDRATE IS:
Cx(H2O)y
EXAMPLES
The formula for glucose is C6H12O6
The formula for sucrose is C12H22O11
The Nature of Carbohydrates
 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:
THE CLASSIFICATION OF CARBOHYDRATES
Carbohydrates are classified as either sugars or polysaccharides
CARBOHYDRATES
SUGARS POLYSACCHARIDES
MONOSACCHARIDES DISACCHARIDES STORAGE STRUCTURAL
Monosaccharides are
single sugar units that
include:
GLUCOSE
FRUCTOSE
GALACTOSE
Disaccharides are
double sugar units that
include:
SUCROSE
MALTOSE
LACTOSE
GLYCOGEN and
STARCH are
storage
carbohydrates;
animal cells store
glucose as
glycogen and
plant cells store
glucose as starch
CELLULOSE
and CHITIN are
important
structural
carbohydrates;
cellulose forms
the fabric of
many cells walls
and chitin is a
major component
of the
exoskeletons of
many arthropodsGLUCOSE
MONOSACCHARIDES
Monosaccharides are single sugar units that form the building blocks for
the larger carbohydrates
There are many different monosaccharides; they vary according to the number
of carbon atoms that they possess and in the way the atoms are arranged
in the molecules
Glucose, the main source of energy for most organisms, is a hexose sugar with
six carbon atoms and the formula C6H12O6
Glucose exists in both straight chain and ring form with rings forming when
glucose is dissolved in water
C
C
C
C
C
C
H
H
H
O
O
O
H
H
H
H
H
O
O
O
H
H
H
H
1
2
3
4
5
6
1
23
4
5
6
C
CH O H
H
C
H
H
O H
H
O H
H
HO
OH
H
C C
C
O
CHAIN STRUCTURE RING STRUCTURE
Classification of Monosaccharides
•The monosaccharides are the simplest of the carbohydrates,
since they contain only one polyhydroxy aldehyde or ketone
unit.
•Monosaccharides are classified according to the number of
carbon atoms they contain:
•Thepresence of an aldehyde is indicated by the prefix aldo-
and a ketone by the prefix keto-.
Monosaccharide
3C- triose (DHAP) glyceraldehyde
4C- tetrose erythrose
5C- pentose arabinose
6C- hexose
ALDEHYDE GROUPC
C
C
C
C
C
H
H
H
O
O
O
H
H
H
H
H
O
O
O
H
H
H
H
1
2
3
4
5
6
GLUCOSE
This straight chain
representation of the glucose
molecule shows how the
carbon atoms are numbered
Glucose, in common with
many other hexose sugars
has an aldehyde group
as part of the structure
The carbon atom that
forms part of this aldehyde
group is always carbon 1
The C = O carbonyl group
has reducing properties such
that all monosaccharides
are reducing sugars
The remainder of the molecule
is a series of bonded carbon
atoms with attached hydrogen
atoms and hydroxyl (OH) groups
The carbon atom
of the carbonyl group
is referred to as the
ANOMERIC CARBON
ATOM and, for glucose,
this is carbon 1
1
23
4
5
6
C
CH O H
H
C
H
H
O H
H
O H
H
HO
OH
H
C C
C
O
GLUCOSE
In solution glucose exists in ring form
Glucose forms a
six-membered ring when
the hydroxyl group (OH)
on carbon 5 adds to the
aldehyde group on
carbon 1
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
+
+
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
α-D-glucose β-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)
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.
Cyclization of glucose produces a new asymmetric center
at C1. The 2 stereoisomers are called anomers, α & β.
Haworth projections represent the cyclic sugars as having
essentially planar rings, with the OH at the anomeric C1:
 α (OH below the ring)
 β (OH above the ring).
H O
OH
H
OHH
OH
CH2OH
H
α-D-glucose
OH
H H O
OH
H
OHH
OH
CH2OH
H
H
OH
β-D-glucose
23
4
5
6
1 1
6
5
4
3 2
GLUCOSE
1
C H O H2
H
H H
H O O H
O H
H O H
H
O
The ring structure of glucose is usually represented in
Howarth projection
ISOMERS
Each hexose sugar exists in both alpha and beta forms
These ISOMERS can be distinguished by the arrangement of the
OH and H groups about the extreme right carbon atom IN the ring
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
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
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
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
Properties of glucose
• Oxidation
• Monosaccharides are easily oxidised by the
oxidising agents.
• With mild reagents such as Tollen’s reagent
Glucose gives Gluconic acid.
Pottasium ferricyanide can be reduced to
ferrocyanide .(test for sugars having free
carbonyl groups. Hence also called
reducing sugars.
• Strong oxidizing agents like Conc nitric acid
yields dicarboxylic acid Saccharic acid.
• Reduction
• Free CHO & C=O of monosacchrides are
reduced to alcohol by sodium amalgam and
water.
• Glucose yields Sorbitol & Mannitol.
• Free CHO & C=O groups of sugar reacts
with phenyl hydrazine to form
corresponding osazone.
• Glucose – Glucosazone
• Reaction with HCN – Cyanohydrin
• Esterification- The hydroxyl group of
alcohols in the carbohydrate may be
converted to esters by treatment with
acetylating agents.(Glucose Penta Acetate)
Formation of Phosphate Esters
•Phosphate esters can form at the 6-carbon of
aldohexoses and aldoketoses.
• •Phosphate esters of monosaccharides are
found in the sugar-phosphate backbone of
DNA and RNA, in ATP, and as intermediates
in the metabolism of carbohydrates in the
body.
• Methylation
• Reacting with methyl alcohol monosaccrides
yields glycosides
• Fermentation
• Mono sacchrides like glucose & fructose
yields ethanol & Carbon dioxide on
hydrolysis
• MUTAROTATION
The two stereoisomeric forms of glucose,
i.e., α-D-glucose and β-D-glucose exist in
separate crystalline forms and thus have
different melting points and specific
rotations. For example α-D-glucose has a
m.p. of 419 K with a specific rotation of
+112° while β-D-glucose has a m.p. of 424
K and has a specific rotation of +19°.
• However, when either of these two forms is
dissolved in water and allowed to stand, it
gets converted into an equilibrium mixture
of α-and β-forms through a small amount of
the open chain form.
• As a result of this equilibrium, the specific
rotation of a freshly prepared solution of α-
D-glucose gradually decreases from of
+112° to +52.7° and that of β-D-glucose
gradually increases from +19° to +52.7°.
•
• This change in specific rotation of an
optically active compound in solution with
time, to an equilibrium value, is called
mutarotation.
• During mutarotation, the ring opens and
then recloses either in the inverted position
or in the original position giving a mixture
of α-and-β-forms.
• All reducing carbohydrates, i.e.,
monosaccharides and disacchardies
(maltose, lactose etc.) undergo mutarotation
in aqueous solution.
Galactose
Ring structure
Fructose
C HHO
C OHH
C OHH
CH2OH
CH2OH
C O
D-fructose
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
α-D-glucopyranose β-D-glucopyranose
1
6
5
4
3
2
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
α-D-glucopyranose
O
H
HO
H
HO
H
OCH3
OHH
H
OH
methyl-α-D-glucopyranose
CH3-OH+
methanol
H2O
Cellobiose, a product of cellulose breakdown, is the
otherwise equivalent β anomer (O on C1 points up).
The β(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
α(1→ 4) glycosidic
link between C1 - C4
OH of 2 glucoses.
It is the α anomer
(C1 O points down).
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 α (O points down from ring), the linkage is α(1→2).
The full name of sucrose is α-D-glucopyranosyl-(1→2)-
β-D-fructopyranose.)
 Lactose, milk sugar, is composed of galactose &
glucose, with β(1→4) linkage from the anomeric OH of
galactose. Its full name is β-D-galactopyranosyl-(1→ 4)-
α-D-glucopyranose
Cellulose, a major constituent of plant cell walls, consists
of long linear chains of glucose with β(1→4) linkages.
Every other glucose is flipped over, due to β 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.
Multisubunit Cellulose Synthase complexes in the plasma
membrane spin out from the cell surface microfibrils
consisting of 36 parallel, interacting cellulose chains.
These microfibrils are very strong.
The role of cellulose is to impart strength and rigidity to
plant cell walls, which can withstand high hydrostatic
pressure gradients. Osmotic swelling is prevented.
Explore and compare structures of amylose & cellulose
using Chime.
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
DISACCHARIDES
Disaccharides are sugars composed of two monosaccharides covalently bonded
together by a glycosidic linkage
Maltose, also known as malt sugar, is formed from two glucose molecules
Lactose, or milk sugar, is a disaccharide formed when the monosaccharides
glucose and galactose bond
Sucrose is common household sugar and is formed when the monosaccharides
glucose and fructose bond
MALTOSE = GLUCOSE + GLUCOSE
LACTOSE = GLUCOSE + GALACTOSE
SUCROSE = GLUCOSE + FRUCTOSE
- H2O
THE FORMATION OF MALTOSE
C H O H2
H
H
H O
H
O H
O H
H O H
H
G L U C O S E
C H O H2
H
H
H O
H
O H
O H
H O H
H
O
G L U C O S E
condensation reaction
1 4α glycosidic bond
Maltose forms
when two alpha
glucose molecules
undergo a
condensation
reaction and form
a glycosidic bond
between the two
molecules
C H O H2
H
H
O H
O H
H O H
H
O
C H O H2
H
H
H O
H
OO H
H
H
O
1
23
4
5
6
1
23
4
5
6
MALTOSE
MALTOSE IS A DISACCHARIDE FORMED WHEN TWO ALPHA
GLUCOSE MOLECULES ARE COVALENTLY BONDED TOGETHER
REDUCING SUGARS
All the monosaccharides and many of the disaccharides are
REDUCING SUGARS
Benedict’s test is used to determine the reducing properties of the
different sugars
If a sugar is a reducing sugar then the Cu2+
(Cupric ions)
ions are reduced to Cu+ (Cuprous)
which, in the
presence of alkaline sodium hydroxide,
form copper oxideCopper oxide is insoluble and precipitates
out of the solution as a brick-red
precipitate
Benedicts solution is a turquoise solution
containing copper ions and sodium
hydroxide; the copper ions exist as Cu2+
in this reagent
REDUCING SUGARS
When Benedicts test is performed with the disaccharides maltose and
sucrose, the following result is obtained:
Sucrose is a
non-reducing sugar
Maltose is a
reducing sugar
SUCROSE
RESULT
MALTOSE
RESULT
REDUCING SUGARS
Why is sucrose a non-reducing sugar?
C H O H2
H
H
O H
O H
H O H
H
O
C H O H2
H
H
H O
H
OO H
H O H
H
O
1
23
4
5
6
1
23
4
5
6
MALTOSE
1
1
2
2
3
3
4
4
5
5
6
6
SUCROSE
Sugars reduce Benedicts solution when the anomeric
carbon atom is made available to reduce the copper
ions in the solution
The anomeric carbon atom is the carbon of the
carbonyl group present in the straight chain form
of the sugar
The anomeric carbon atom for glucose
is carbon 1
C
C
C
C
C
C
H
H
H
O
O
O
H
H
H
H
H
O
O
O
H
H
H
H
1
2
3
4
5
6
REDUCING SUGARS
Why is sucrose a non-reducing sugar?
C H O H2
H
H
O H
O H
H O H
H
O
C H O H2
H
H
H O
H
OO H
H O H
H
O
1
23
4
5
6
1
23
4
5
6
MALTOSE
1
1
2
2
3
3
4
4
5
5
6
6
SUCROSE
The anomeric carbon atom for fructose
is carbon 2
C
C
C
C
C
C
H
H
O
O
O
H
H
H
H
H
H
O
O
O
H
H
H
H
1
2
3
4
5
6
Fructose bonds to glucose to form
sucrose
Sugars reduce Benedicts solution when the anomeric
carbon atom is made available to reduce the copper
ions in the solution
Why is sucrose a non-reducing sugar?
C H O H2
H
H
O H
O H
H O H
H
O
C H O H2
H
H
H O
H
OO H
H O H
H
O
1
23
4
5
6
1
23
4
5
6
MALTOSE
1
1
2
2
3
3
4
4
5
5
6
6
SUCROSE
When maltose is boiled with Benedict’s reagent, the
region of the ring containing the anomeric carbon
atom (carbon 1) may open exposing a carbonyl
group capable of reducing Benedicts reagent – ONLY
AN ANOMERIC CARBON ATOM THAT IS NOT
INVOLVED IN THE FORMATION OF THE
GLYCOSIDIC BOND MAY BE EXPOSED
This potential anomeric carbon
atom is available to reduce
Benedict’s reagent
This potential anomeric carbon
atom is unavailable
The one available anomeric carbon atom is sufficient
for this molecule to reduce Benedict’s solution and
thus MALTOSE is a reducing sugar
1
1
2
2
3
3
4
4
5
5
6
6
SUCROSE
C
C
C
C
C
C
H
H
O
O
O
H
H
H
H
H
H
O
O
O
H
H
H
H
1
2
3
4
5
6
Sucrose is formed when glucose forms a glycosidic bond
with fructose
glucose
fructose
glycosidic
bond
The anomeric carbon
atom for fructose
is carbon 2
C
C
C
C
C
C
H
H
H
O
O
O
H
H
H
H
H
O
O
O
H
H
H
H
1
2
3
4
5
6
The anomeric carbon
atom for glucose
is carbon 1
As both the anomeric carbon atoms are involved in forming
the glycosidic bond when glucose and fructose join,
there are no potentially free anomeric carbon atoms available
to reduce Benedict’s solution
SUCROSE IS A NON-REDUCING SUGAR
TEST FOR SUCROSE
In order to determine if sucrose is present in a sample or solution then the
following procedure is performed;
The sample or solution under consideration is boiled for at least fifteen minutes
in hydrochloric acid
Boiling in acid breaks glycosidic bonds – the glycosidic bond is hydrolysed
This procedure is called ACID HYDROLYSIS
The solution is then neutralised by adding drops of alkali while testing
with pH paper
Benedict’s test is now performed on the resulting solution
If a brick-red precipitate forms then sucrose was present in the original solution
Acid hydrolysis breaks the glycosidic bonds in the sucrose molecules
releasing free glucose and free fructose into the solution
Glucose and fructose are both monosaccharides and therefore reducing sugars
If no precipitate is obtained then sucrose was not present in the original sample
The need to neutralise the solution following acid hydrolysis is due to the
fact that the Benedict’s test requires an alkaline medium
POLYSACCHARIDES
Polysaccharides are large polymers of the monosaccharides
Unlike monosaccharides and disaccharides, polysaccharides are either
insoluble or form colloidal suspensions
The principal storage polysaccharides are STARCH AND GLYCOGEN
Starch is a polymer of alpha glucose and is, in fact, a mixture of
two different polysaccharides – AMYLOSE AND AMYLOPECTIN
STARCH
AMYLOSE – long unbranched chain of glucose
units
AMYLOPECTIN – highly branched polymer
of glucose units
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 α(1→4) linkages.
The end of the polysaccharide with an anomeric C1 not involved in a
glycosidic bond is called the reducing end.
Soluble in water, formed of 300-400 glucose units.
End of the chain have reducing property.
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
Amylopectin is a glucose polymer with mainly α(1→4) linkages, but
it also has branches formed by α(1→6) linkages. Branches are
generally longer than shown above.
The branches produce a compact structure & provide multiple chain
ends at which enzymatic cleavage can occur.
Insoluble in water
Partially digested form is called dextrin.
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
Glycogen, the glucose storage polymer in animals, is
similar in structure to amylopectin.
But glycogen has more α(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.
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
AMYLOSE STRUCTURE
C H O H2
H
H
H O
H
OO H
H O H
H
O
C H O H2
H
H H
OO H
H O H
H
O
C H O H2
H
H H
OO H
H O H
H
O
G L U C O S E G L U C O S EG L U C O S E
Amylose is formed by a series of condensation reactions that bond
alpha glucose molecules together into a long chain
forming many glycosidic bonds
The amylose chain, once formed, coils into a helix
AMYLOSE STRUCTURE
O
O
O
O
O
O
O
O
O
O
O
O
O
OO
OOO
OO
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
THE AMYLOSE HELIX
AMYLOPECTIN STRUCTURE
O
C H O H2
H
H
H O
H
OO H
H O H
H
O
C H O H2
H
H H
O H
H O H
H
O
G L U C O S E G L U C O S E
C H O H2
H
H
H O
H
OO H
H O H
H
O
C H O H2
H
H H
OO H
H O H
H
O
C H 2
H
H H
OO H
H O H
H
O
G L U C O S E G L U C O S EG L U C O S E
B r a n c h p o in t
1 6 g ly c o s id ic b o n d
1 4 c h a in
6
1
Amylopectin consists of a straight chain of alpha glucose units with branch points
occurring at approximately every twelth glucose unit along the straight chain
The branch points form when carbon 6 of a glucose molecule in the straight chain
forms a glycosidic bond with carbon 1 of a glucose molecule positioned above
the chain
AMYLOPECTIN STRUCTURE
This highly branched amylopectin molecule is wrapped around the amylose to
make up the final starch molecule
This large insoluble molecule with branch points that allow for easy
access for enzymes when breaking down the molecule, makes
starch an ideal food storage compound
REACTION BETWEEN STARCH AND IODINE SOLUTION
When iodine solution is added to a suspension of starch, the iodine
molecules pack inside the amylose helix to give a blue-black colour
When iodine reacts with the starch in a
piece of bread, the bread itself develops
the blue-black colour
N.B. Iodine is virtually insoluble in water – ‘Iodine Solution’ is really
iodine dissolved in an aqueous solution of Potassium Iodide (KI)
GLYCOGEN
GLUCOSE IS STORED AS GLYCOGEN IN
LARGE AMOUNTS IN BOTH THE LIVER
AND SKELETAL MUSCLES
GLYCOGEN
Glycogen is often referred to as animal starch
Glycogen has the same overall structure as amylopectin but
there is significantly more branching in this molecule
O
C H O H2
H
H
H O
H
OO H
H O H
H
O
C H O H2
H
H H
O H
H O H
H
O
G L U C O S E G L U C O S E
C H O H2
H
H
H O
H
OO H
H O H
H
O
C H O H2
H
H H
OO H
H O H
H
O
C H 2
H
H H
OO H
H O H
H
O
G L U C O S E G L U C O S EG L U C O S E
B r a n c h p o in t
1 6 g ly c o s id ic b o n d
1 4 c h a in
6
1
More of these
branch points form
STRUCTURAL POYSACCHARIDES
Cellulose is one of the most important structural polysaccharides as it is the
major component of plant cell walls
1 4 glycosidic bonds
O
O
CH OH2
H
OH
H OH
H
O
GLUCOSE
1
23
4
5
6
H
OH
H OH
H
O
CH OH2
GLUCOSE
3 2
1
6
5
4
O
CH OH2
H
H
HO
OH
H OH
H
O
GLUCOSE
1
23
4
5
6
H
OH
H OH
H
O
CH OH2
GLUCOSE
3 2
1
6
5
4
Cellulose is a polymer of beta glucose units where each glucose molecule
is inverted with respect to its neighbour
The orientation of the beta glucose units places many hydroxyl (OH) groups
on each side of the molecule
Many parallel chains of beta glucose units form and each chain forms hydrogen
bonds between the OH groups of adjacent chains
STRUCTURAL POYSACCHARIDES
The bundles of parallel chains forming hydrogen bonds
with each other creates a molecule that confers rigidity
and strength to the structures of which they form a part
The rigidity and strength of plant cell walls is a consequence
of the incorporation of cellulose into their structure
hydrogen bonds between parallel chains of beta glucose
STRUCTURAL POYSACCHARIDES
Chitin is a polysaccharide forming the exoskeletons of many
invertebrates. It is a polymer of N-acetylglucosamine in beta 1 to
4 glycosidic linkage. It is the major element in the exoskeleton of
insects and crustacea where it affords protection and support.
N - A c e t y lg lu c o s a m in e
CHITIN
Benedict’s Reagent
Sucrose (table sugar) contains two sugars
(fructose and glucose) joined by their glycosidic
bond in such a way as to prevent the glucose
isomerizing to aldehyde, or the fructose to alpha-
hydroxy-ketone form.
Sucrose is thus a non-reducing sugar which does
not react with Benedict's reagent..
The products of sucrose decomposition are
glucose and fructose, both of which can be
detected by Benedict's reagent.
• The Benedict’s test is used to differentiate
between reducing and nonreducing sugars.
• In the test, Cu2+ is reduced to Cu+ and the
reducing sugar is oxidized to a carboxylic acid
• The appearance of copper (I) oxide, which is
brick red, confirms the sugar to be a reducing
sugar.
• Nonreducing sugars do not react.
• Iodine Test
• The iodine test is used to differentiate between starch and
glycogen.
• Starch contains amylose, a polymeric chain of glucose residues
bonded together by a-1,4’ linkages. Amylose form an a-helix.
• Molecular iodine can intercalate into the a-helical structure. The
resulting complex is bluish black.
• The extensive branching of glycogen deters the formation of an
a-helix. The addition of molecular iodine to a solution of
glycogen does not give a bluish black color; instead, the color of
the solution is reddish purple
• Osazone Formation
• Osazones are formed by the reaction of a sugar with
phenylhydrazine.
• An osazone is a solid derivative of a sugar containing two
phenylhydrazone moieties. From the observation
of the rate at which the osazone forms and the appearance
of the precipitate can differentiate between
• epimeric sugars.
• Osazones form at different rates for different sugars:
fructose reacts very rapidly, while glucose takes longer to
react. The appearance of the precipitate can also be
different.
• The crystalstructure ranges from coarse (for glucose) to
very fine (for arabinose).
• Barfoed’s Test
• The Barfoed’s test also differentiates between
reducing and nonreducing sugars, but because
it is more sensitive than the Benedict’s test,
• it can be used to differentiate between
reducing monosaccharides and reducing
disaccharides.
• The reduction of Cu2+ to copper (I) oxide
occurs more rapidly for monosaccharides than
for disaccharides.
Acknowledgements
Copyright © 2003 SSER Ltd. and its licensors.
All rights reserved. All graphics are for viewing purposes only.
The nature of carbohydrates

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The nature of carbohydrates

  • 1. © SSER Ltd. OPTOM FASLU MUHAMMED
  • 2. Carbohydrates are compounds of great importance in both the biological and commercial world They are used as a source of energy in all organisms and as structural materials in membranes, cell walls and the exoskeletons of many arthropods All carbohydrates contain the elements carbon (C), hydrogen (H) and oxygen (O) with the hydrogen and oxygen being present in a 2 : 1 ratio THE GENERAL FORMULA OF A CARBOHYDRATE IS: Cx(H2O)y EXAMPLES The formula for glucose is C6H12O6 The formula for sucrose is C12H22O11 The Nature of Carbohydrates
  • 3.  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:
  • 4. THE CLASSIFICATION OF CARBOHYDRATES Carbohydrates are classified as either sugars or polysaccharides CARBOHYDRATES SUGARS POLYSACCHARIDES MONOSACCHARIDES DISACCHARIDES STORAGE STRUCTURAL Monosaccharides are single sugar units that include: GLUCOSE FRUCTOSE GALACTOSE Disaccharides are double sugar units that include: SUCROSE MALTOSE LACTOSE GLYCOGEN and STARCH are storage carbohydrates; animal cells store glucose as glycogen and plant cells store glucose as starch CELLULOSE and CHITIN are important structural carbohydrates; cellulose forms the fabric of many cells walls and chitin is a major component of the exoskeletons of many arthropodsGLUCOSE
  • 5. MONOSACCHARIDES Monosaccharides are single sugar units that form the building blocks for the larger carbohydrates There are many different monosaccharides; they vary according to the number of carbon atoms that they possess and in the way the atoms are arranged in the molecules Glucose, the main source of energy for most organisms, is a hexose sugar with six carbon atoms and the formula C6H12O6 Glucose exists in both straight chain and ring form with rings forming when glucose is dissolved in water C C C C C C H H H O O O H H H H H O O O H H H H 1 2 3 4 5 6 1 23 4 5 6 C CH O H H C H H O H H O H H HO OH H C C C O CHAIN STRUCTURE RING STRUCTURE
  • 6. Classification of Monosaccharides •The monosaccharides are the simplest of the carbohydrates, since they contain only one polyhydroxy aldehyde or ketone unit. •Monosaccharides are classified according to the number of carbon atoms they contain: •Thepresence of an aldehyde is indicated by the prefix aldo- and a ketone by the prefix keto-. Monosaccharide 3C- triose (DHAP) glyceraldehyde 4C- tetrose erythrose 5C- pentose arabinose 6C- hexose
  • 7. ALDEHYDE GROUPC C C C C C H H H O O O H H H H H O O O H H H H 1 2 3 4 5 6 GLUCOSE This straight chain representation of the glucose molecule shows how the carbon atoms are numbered Glucose, in common with many other hexose sugars has an aldehyde group as part of the structure The carbon atom that forms part of this aldehyde group is always carbon 1 The C = O carbonyl group has reducing properties such that all monosaccharides are reducing sugars The remainder of the molecule is a series of bonded carbon atoms with attached hydrogen atoms and hydroxyl (OH) groups The carbon atom of the carbonyl group is referred to as the ANOMERIC CARBON ATOM and, for glucose, this is carbon 1
  • 8. 1 23 4 5 6 C CH O H H C H H O H H O H H HO OH H C C C O GLUCOSE In solution glucose exists in ring form Glucose forms a six-membered ring when the hydroxyl group (OH) on carbon 5 adds to the aldehyde group on carbon 1
  • 9. 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 + +
  • 10. 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 α-D-glucose β-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)
  • 11. 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.
  • 12. Cyclization of glucose produces a new asymmetric center at C1. The 2 stereoisomers are called anomers, α & β. Haworth projections represent the cyclic sugars as having essentially planar rings, with the OH at the anomeric C1:  α (OH below the ring)  β (OH above the ring). H O OH H OHH OH CH2OH H α-D-glucose OH H H O OH H OHH OH CH2OH H H OH β-D-glucose 23 4 5 6 1 1 6 5 4 3 2
  • 13. GLUCOSE 1 C H O H2 H H H H O O H O H H O H H O The ring structure of glucose is usually represented in Howarth projection
  • 14. ISOMERS Each hexose sugar exists in both alpha and beta forms These ISOMERS can be distinguished by the arrangement of the OH and H groups about the extreme right carbon atom IN the ring
  • 15. 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
  • 16. 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
  • 17. 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
  • 18. 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
  • 19. Properties of glucose • Oxidation • Monosaccharides are easily oxidised by the oxidising agents. • With mild reagents such as Tollen’s reagent Glucose gives Gluconic acid. Pottasium ferricyanide can be reduced to ferrocyanide .(test for sugars having free carbonyl groups. Hence also called reducing sugars.
  • 20. • Strong oxidizing agents like Conc nitric acid yields dicarboxylic acid Saccharic acid. • Reduction • Free CHO & C=O of monosacchrides are reduced to alcohol by sodium amalgam and water. • Glucose yields Sorbitol & Mannitol.
  • 21. • Free CHO & C=O groups of sugar reacts with phenyl hydrazine to form corresponding osazone. • Glucose – Glucosazone • Reaction with HCN – Cyanohydrin • Esterification- The hydroxyl group of alcohols in the carbohydrate may be converted to esters by treatment with acetylating agents.(Glucose Penta Acetate)
  • 22. Formation of Phosphate Esters •Phosphate esters can form at the 6-carbon of aldohexoses and aldoketoses. • •Phosphate esters of monosaccharides are found in the sugar-phosphate backbone of DNA and RNA, in ATP, and as intermediates in the metabolism of carbohydrates in the body.
  • 23. • Methylation • Reacting with methyl alcohol monosaccrides yields glycosides • Fermentation • Mono sacchrides like glucose & fructose yields ethanol & Carbon dioxide on hydrolysis
  • 24. • MUTAROTATION The two stereoisomeric forms of glucose, i.e., α-D-glucose and β-D-glucose exist in separate crystalline forms and thus have different melting points and specific rotations. For example α-D-glucose has a m.p. of 419 K with a specific rotation of +112° while β-D-glucose has a m.p. of 424 K and has a specific rotation of +19°.
  • 25. • However, when either of these two forms is dissolved in water and allowed to stand, it gets converted into an equilibrium mixture of α-and β-forms through a small amount of the open chain form. • As a result of this equilibrium, the specific rotation of a freshly prepared solution of α- D-glucose gradually decreases from of +112° to +52.7° and that of β-D-glucose gradually increases from +19° to +52.7°. •
  • 26. • This change in specific rotation of an optically active compound in solution with time, to an equilibrium value, is called mutarotation. • During mutarotation, the ring opens and then recloses either in the inverted position or in the original position giving a mixture of α-and-β-forms. • All reducing carbohydrates, i.e., monosaccharides and disacchardies (maltose, lactose etc.) undergo mutarotation in aqueous solution.
  • 29. Fructose C HHO C OHH C OHH CH2OH CH2OH C O D-fructose
  • 30. 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 α-D-glucopyranose β-D-glucopyranose 1 6 5 4 3 2
  • 31. 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 α-D-glucopyranose O H HO H HO H OCH3 OHH H OH methyl-α-D-glucopyranose CH3-OH+ methanol H2O
  • 32. Cellobiose, a product of cellulose breakdown, is the otherwise equivalent β anomer (O on C1 points up). The β(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 α(1→ 4) glycosidic link between C1 - C4 OH of 2 glucoses. It is the α anomer (C1 O points down).
  • 33. 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 α (O points down from ring), the linkage is α(1→2). The full name of sucrose is α-D-glucopyranosyl-(1→2)- β-D-fructopyranose.)  Lactose, milk sugar, is composed of galactose & glucose, with β(1→4) linkage from the anomeric OH of galactose. Its full name is β-D-galactopyranosyl-(1→ 4)- α-D-glucopyranose
  • 34. Cellulose, a major constituent of plant cell walls, consists of long linear chains of glucose with β(1→4) linkages. Every other glucose is flipped over, due to β 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.
  • 35. Multisubunit Cellulose Synthase complexes in the plasma membrane spin out from the cell surface microfibrils consisting of 36 parallel, interacting cellulose chains. These microfibrils are very strong. The role of cellulose is to impart strength and rigidity to plant cell walls, which can withstand high hydrostatic pressure gradients. Osmotic swelling is prevented. Explore and compare structures of amylose & cellulose using Chime. 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
  • 36. DISACCHARIDES Disaccharides are sugars composed of two monosaccharides covalently bonded together by a glycosidic linkage Maltose, also known as malt sugar, is formed from two glucose molecules Lactose, or milk sugar, is a disaccharide formed when the monosaccharides glucose and galactose bond Sucrose is common household sugar and is formed when the monosaccharides glucose and fructose bond MALTOSE = GLUCOSE + GLUCOSE LACTOSE = GLUCOSE + GALACTOSE SUCROSE = GLUCOSE + FRUCTOSE
  • 37. - H2O THE FORMATION OF MALTOSE C H O H2 H H H O H O H O H H O H H G L U C O S E C H O H2 H H H O H O H O H H O H H O G L U C O S E condensation reaction 1 4α glycosidic bond Maltose forms when two alpha glucose molecules undergo a condensation reaction and form a glycosidic bond between the two molecules C H O H2 H H O H O H H O H H O C H O H2 H H H O H OO H H H O 1 23 4 5 6 1 23 4 5 6 MALTOSE MALTOSE IS A DISACCHARIDE FORMED WHEN TWO ALPHA GLUCOSE MOLECULES ARE COVALENTLY BONDED TOGETHER
  • 38. REDUCING SUGARS All the monosaccharides and many of the disaccharides are REDUCING SUGARS Benedict’s test is used to determine the reducing properties of the different sugars If a sugar is a reducing sugar then the Cu2+ (Cupric ions) ions are reduced to Cu+ (Cuprous) which, in the presence of alkaline sodium hydroxide, form copper oxideCopper oxide is insoluble and precipitates out of the solution as a brick-red precipitate Benedicts solution is a turquoise solution containing copper ions and sodium hydroxide; the copper ions exist as Cu2+ in this reagent
  • 39. REDUCING SUGARS When Benedicts test is performed with the disaccharides maltose and sucrose, the following result is obtained: Sucrose is a non-reducing sugar Maltose is a reducing sugar SUCROSE RESULT MALTOSE RESULT
  • 40. REDUCING SUGARS Why is sucrose a non-reducing sugar? C H O H2 H H O H O H H O H H O C H O H2 H H H O H OO H H O H H O 1 23 4 5 6 1 23 4 5 6 MALTOSE 1 1 2 2 3 3 4 4 5 5 6 6 SUCROSE Sugars reduce Benedicts solution when the anomeric carbon atom is made available to reduce the copper ions in the solution The anomeric carbon atom is the carbon of the carbonyl group present in the straight chain form of the sugar The anomeric carbon atom for glucose is carbon 1 C C C C C C H H H O O O H H H H H O O O H H H H 1 2 3 4 5 6
  • 41. REDUCING SUGARS Why is sucrose a non-reducing sugar? C H O H2 H H O H O H H O H H O C H O H2 H H H O H OO H H O H H O 1 23 4 5 6 1 23 4 5 6 MALTOSE 1 1 2 2 3 3 4 4 5 5 6 6 SUCROSE The anomeric carbon atom for fructose is carbon 2 C C C C C C H H O O O H H H H H H O O O H H H H 1 2 3 4 5 6 Fructose bonds to glucose to form sucrose Sugars reduce Benedicts solution when the anomeric carbon atom is made available to reduce the copper ions in the solution
  • 42. Why is sucrose a non-reducing sugar? C H O H2 H H O H O H H O H H O C H O H2 H H H O H OO H H O H H O 1 23 4 5 6 1 23 4 5 6 MALTOSE 1 1 2 2 3 3 4 4 5 5 6 6 SUCROSE When maltose is boiled with Benedict’s reagent, the region of the ring containing the anomeric carbon atom (carbon 1) may open exposing a carbonyl group capable of reducing Benedicts reagent – ONLY AN ANOMERIC CARBON ATOM THAT IS NOT INVOLVED IN THE FORMATION OF THE GLYCOSIDIC BOND MAY BE EXPOSED This potential anomeric carbon atom is available to reduce Benedict’s reagent This potential anomeric carbon atom is unavailable The one available anomeric carbon atom is sufficient for this molecule to reduce Benedict’s solution and thus MALTOSE is a reducing sugar
  • 43. 1 1 2 2 3 3 4 4 5 5 6 6 SUCROSE C C C C C C H H O O O H H H H H H O O O H H H H 1 2 3 4 5 6 Sucrose is formed when glucose forms a glycosidic bond with fructose glucose fructose glycosidic bond The anomeric carbon atom for fructose is carbon 2 C C C C C C H H H O O O H H H H H O O O H H H H 1 2 3 4 5 6 The anomeric carbon atom for glucose is carbon 1 As both the anomeric carbon atoms are involved in forming the glycosidic bond when glucose and fructose join, there are no potentially free anomeric carbon atoms available to reduce Benedict’s solution SUCROSE IS A NON-REDUCING SUGAR
  • 44. TEST FOR SUCROSE In order to determine if sucrose is present in a sample or solution then the following procedure is performed; The sample or solution under consideration is boiled for at least fifteen minutes in hydrochloric acid Boiling in acid breaks glycosidic bonds – the glycosidic bond is hydrolysed This procedure is called ACID HYDROLYSIS The solution is then neutralised by adding drops of alkali while testing with pH paper Benedict’s test is now performed on the resulting solution If a brick-red precipitate forms then sucrose was present in the original solution Acid hydrolysis breaks the glycosidic bonds in the sucrose molecules releasing free glucose and free fructose into the solution Glucose and fructose are both monosaccharides and therefore reducing sugars If no precipitate is obtained then sucrose was not present in the original sample The need to neutralise the solution following acid hydrolysis is due to the fact that the Benedict’s test requires an alkaline medium
  • 45. POLYSACCHARIDES Polysaccharides are large polymers of the monosaccharides Unlike monosaccharides and disaccharides, polysaccharides are either insoluble or form colloidal suspensions The principal storage polysaccharides are STARCH AND GLYCOGEN Starch is a polymer of alpha glucose and is, in fact, a mixture of two different polysaccharides – AMYLOSE AND AMYLOPECTIN STARCH AMYLOSE – long unbranched chain of glucose units AMYLOPECTIN – highly branched polymer of glucose units
  • 46. 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 α(1→4) linkages. The end of the polysaccharide with an anomeric C1 not involved in a glycosidic bond is called the reducing end. Soluble in water, formed of 300-400 glucose units. End of the chain have reducing property. 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
  • 47. Amylopectin is a glucose polymer with mainly α(1→4) linkages, but it also has branches formed by α(1→6) linkages. Branches are generally longer than shown above. The branches produce a compact structure & provide multiple chain ends at which enzymatic cleavage can occur. Insoluble in water Partially digested form is called dextrin. 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
  • 48. Glycogen, the glucose storage polymer in animals, is similar in structure to amylopectin. But glycogen has more α(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. 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
  • 49. AMYLOSE STRUCTURE C H O H2 H H H O H OO H H O H H O C H O H2 H H H OO H H O H H O C H O H2 H H H OO H H O H H O G L U C O S E G L U C O S EG L U C O S E Amylose is formed by a series of condensation reactions that bond alpha glucose molecules together into a long chain forming many glycosidic bonds The amylose chain, once formed, coils into a helix
  • 51. AMYLOPECTIN STRUCTURE O C H O H2 H H H O H OO H H O H H O C H O H2 H H H O H H O H H O G L U C O S E G L U C O S E C H O H2 H H H O H OO H H O H H O C H O H2 H H H OO H H O H H O C H 2 H H H OO H H O H H O G L U C O S E G L U C O S EG L U C O S E B r a n c h p o in t 1 6 g ly c o s id ic b o n d 1 4 c h a in 6 1 Amylopectin consists of a straight chain of alpha glucose units with branch points occurring at approximately every twelth glucose unit along the straight chain The branch points form when carbon 6 of a glucose molecule in the straight chain forms a glycosidic bond with carbon 1 of a glucose molecule positioned above the chain
  • 52. AMYLOPECTIN STRUCTURE This highly branched amylopectin molecule is wrapped around the amylose to make up the final starch molecule This large insoluble molecule with branch points that allow for easy access for enzymes when breaking down the molecule, makes starch an ideal food storage compound
  • 53. REACTION BETWEEN STARCH AND IODINE SOLUTION When iodine solution is added to a suspension of starch, the iodine molecules pack inside the amylose helix to give a blue-black colour When iodine reacts with the starch in a piece of bread, the bread itself develops the blue-black colour N.B. Iodine is virtually insoluble in water – ‘Iodine Solution’ is really iodine dissolved in an aqueous solution of Potassium Iodide (KI)
  • 54. GLYCOGEN GLUCOSE IS STORED AS GLYCOGEN IN LARGE AMOUNTS IN BOTH THE LIVER AND SKELETAL MUSCLES
  • 55. GLYCOGEN Glycogen is often referred to as animal starch Glycogen has the same overall structure as amylopectin but there is significantly more branching in this molecule O C H O H2 H H H O H OO H H O H H O C H O H2 H H H O H H O H H O G L U C O S E G L U C O S E C H O H2 H H H O H OO H H O H H O C H O H2 H H H OO H H O H H O C H 2 H H H OO H H O H H O G L U C O S E G L U C O S EG L U C O S E B r a n c h p o in t 1 6 g ly c o s id ic b o n d 1 4 c h a in 6 1 More of these branch points form
  • 56. STRUCTURAL POYSACCHARIDES Cellulose is one of the most important structural polysaccharides as it is the major component of plant cell walls 1 4 glycosidic bonds O O CH OH2 H OH H OH H O GLUCOSE 1 23 4 5 6 H OH H OH H O CH OH2 GLUCOSE 3 2 1 6 5 4 O CH OH2 H H HO OH H OH H O GLUCOSE 1 23 4 5 6 H OH H OH H O CH OH2 GLUCOSE 3 2 1 6 5 4 Cellulose is a polymer of beta glucose units where each glucose molecule is inverted with respect to its neighbour The orientation of the beta glucose units places many hydroxyl (OH) groups on each side of the molecule Many parallel chains of beta glucose units form and each chain forms hydrogen bonds between the OH groups of adjacent chains
  • 57. STRUCTURAL POYSACCHARIDES The bundles of parallel chains forming hydrogen bonds with each other creates a molecule that confers rigidity and strength to the structures of which they form a part The rigidity and strength of plant cell walls is a consequence of the incorporation of cellulose into their structure hydrogen bonds between parallel chains of beta glucose
  • 58. STRUCTURAL POYSACCHARIDES Chitin is a polysaccharide forming the exoskeletons of many invertebrates. It is a polymer of N-acetylglucosamine in beta 1 to 4 glycosidic linkage. It is the major element in the exoskeleton of insects and crustacea where it affords protection and support. N - A c e t y lg lu c o s a m in e CHITIN
  • 59. Benedict’s Reagent Sucrose (table sugar) contains two sugars (fructose and glucose) joined by their glycosidic bond in such a way as to prevent the glucose isomerizing to aldehyde, or the fructose to alpha- hydroxy-ketone form. Sucrose is thus a non-reducing sugar which does not react with Benedict's reagent.. The products of sucrose decomposition are glucose and fructose, both of which can be detected by Benedict's reagent.
  • 60. • The Benedict’s test is used to differentiate between reducing and nonreducing sugars. • In the test, Cu2+ is reduced to Cu+ and the reducing sugar is oxidized to a carboxylic acid • The appearance of copper (I) oxide, which is brick red, confirms the sugar to be a reducing sugar. • Nonreducing sugars do not react.
  • 61. • Iodine Test • The iodine test is used to differentiate between starch and glycogen. • Starch contains amylose, a polymeric chain of glucose residues bonded together by a-1,4’ linkages. Amylose form an a-helix. • Molecular iodine can intercalate into the a-helical structure. The resulting complex is bluish black. • The extensive branching of glycogen deters the formation of an a-helix. The addition of molecular iodine to a solution of glycogen does not give a bluish black color; instead, the color of the solution is reddish purple
  • 62. • Osazone Formation • Osazones are formed by the reaction of a sugar with phenylhydrazine. • An osazone is a solid derivative of a sugar containing two phenylhydrazone moieties. From the observation of the rate at which the osazone forms and the appearance of the precipitate can differentiate between • epimeric sugars. • Osazones form at different rates for different sugars: fructose reacts very rapidly, while glucose takes longer to react. The appearance of the precipitate can also be different. • The crystalstructure ranges from coarse (for glucose) to very fine (for arabinose).
  • 63. • Barfoed’s Test • The Barfoed’s test also differentiates between reducing and nonreducing sugars, but because it is more sensitive than the Benedict’s test, • it can be used to differentiate between reducing monosaccharides and reducing disaccharides. • The reduction of Cu2+ to copper (I) oxide occurs more rapidly for monosaccharides than for disaccharides.
  • 64. Acknowledgements Copyright © 2003 SSER Ltd. and its licensors. All rights reserved. All graphics are for viewing purposes only.