Carbohydrates are the sugars, starches and fibers found in fruits, grains, vegetables and milk products. Though often maligned in trendy diets, carbohydrates — one of the basic food groups — are important to a healthy life.

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 forglucose is C6H12O6
The formula forsucrose is C12H22O11
The Nature of Carbohydrates

3. THE CLASSIFICATION OF CARBOHYDRATES
Carbohydrates are classified as eithersugars orpolysaccharides
CARBOHYDRATES
SUGARS POLYSACCHARIDES
MONOSACCHARIDES DISACCHARIDES STORAGE STRUCTURAL
Monosaccharides are
single sugarunits that
include:
GLUCOSE
FRUCTOSE
GALACTOSE
Disaccharides are
double sugarunits that
include:
SUCROSE
MALTOSE
LACTOSE
GLYCOGEN and
STARCHare
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
majorcomponent
of the
exoskeletons of
many arthropodsGLUCOSE

4. MONOSACCHARIDES
Monosaccharides are single sugarunits that formthe building blocks for
the largercarbohydrates
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 formost organisms, is a hexose sugarwith
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

5. ISOMERS
Each hexose sugarexists in both alpha and beta forms
These ISOMERS can be distinguished by the arrangement of the
OHand Hgroups about the extreme right carbon atom IN the ring

6. DISACCHARIDES
Disaccharides are sugars composed of two monosaccharides covalently bonded
togetherby a glycosidic linkage
Maltose, also known as malt sugar, is formed from two glucose molecules
Lactose, ormilksugar, is a disaccharide formed when the monosaccharides
glucose and galactose bond
Sucrose is common household sugarand is formed when the monosaccharides
glucose and fructose bond
MALTOSE = GLUCOSE + GLUCOSE
LACTOSE = GLUCOSE + GALACTOSE
SUCROSE = GLUCOSE + FRUCTOSE

7. - 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 FORMEDWHEN TWOALPHA
GLUCOSE MOLECULES ARE COVALENTLY BONDEDTOGETHER

8. 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 sugaris a reducing sugarthen the Cu2+
ions are reduced to Cu+
which, in the
presence of alkaline sodiumhydroxide,
formcopperoxide
Copperoxide is insoluble and precipitates
out of the solution as a brick-red
precipitate
Benedicts solution is a turquoise solution
containing copperions and sodium
hydroxide; the copperions exist as Cu2+
in this reagent

9. 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

10. TEST FORSUCROSE
In orderto determine if sucrose is present in a sample orsolution then the
following procedure is performed;
The sample orsolution underconsideration is boiled forat least fifteen minutes
in hydrochloric acid
Boiling in acid breaks glycosidic bonds – the glycosidic bond is hydrolysed
This procedure is called ACIDHYDROLYSIS
The solution is then neutralised by adding drops of alkali while testing
with pHpaper
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

11. POLYSACCHARIDES
Polysaccharides are large polymers of the monosaccharides
Unlike monosaccharides and disaccharides, polysaccharides are either
insoluble orform colloidal suspensions
The principal storage polysaccharides are STARCHANDGLYCOGEN
Starch is a polymerof alpha glucose and is, in fact, a mixture of
two different polysaccharides – AMYLOSE ANDAMYLOPECTIN
STARCH
AMYLOSE – long unbranched chain of glucose
units
AMYLOPECTIN – highly branched polymer
of glucose units

12. 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 togetherinto a long chain
forming many glycosidic bonds
The amylose chain, once formed, coils into a helix

13. 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

14. 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 formwhen 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

15. 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 foreasy
access forenzymes when breaking down the molecule, makes
starch an ideal food storage compound

16. REACTION BETWEEN STARCHANDIODINE SOLUTION
When iodine solution is added to a suspension of starch, the iodine
molecules packinside the amylose helix to give a blue-blackcolour
When iodine reacts with the starch in a
piece of bread, the bread itself develops
the blue-blackcolour
N.B. Iodine is virtually insoluble in water – ‘Iodine Solution’ is
really iodine dissolved in an aqueous solution of Potassium

17. 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

18. GLYCOGEN
GLUCOSE IS STOREDAS GLYCOGEN IN
LARGE AMOUNTS IN BOTHTHE LIVER
ANDSKELETAL MUSCLES

19. STRUCTURAL POYSACCHARIDES
Cellulose is one of the most important structural polysaccharides as it is the
majorcomponent 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 polymerof 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 OHgroups of adjacent chains

20. STRUCTURAL POYSACCHARIDES
The bundles of parallel chains forming hydrogen bonds
with each othercreates a molecule that confers rigidity
and strength to the structures of which they forma part
The rigidity and strength of plant cell walls is a consequence
of the incorporation of cellulose into theirstructure
hydrogen bonds between parallel chains of beta glucose

21. STRUCTURAL POYSACCHARIDES
Chitin is a polysaccharide forming the exoskeletons of many invertebrates. It is a
polymerof 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