Download CH 2 OH

 Carbohydrates are polyhydroxy aldehydes or ketones.
 They are represented with general formulae Cn(H2O)n.
 They are the chief source of energy in human body.
50-60% of daily energy requirment is derived from
carbohydrate oxidation.
 Carbohydrates are classified according to the hydrolysis
products into four main groups as follows:
I- Monosaccharides: contain one basic sugar unit.
II- Disaccharides: contain 2 monosaccharide units per
molecule.
III- Oligosaccharides: contain from 3 to 10 monosaccharide
units per molecule.
IV- Polysaccharides: contain more than 10 monosaccharide
units per molecule.
I- MONOSACCHARIDES
 Monosaccharides are the simplest sugars, they are
crystalline water soluble sweet carbohydrates.
 Monosaccharides are classified according to the presence
of aldehyde or ketone group into:

aldoses.

ketoses.
 Each class is further subclassified according to the
number of carbons in the molecule into trioses (3
carbons), tetroses (4 carbons), pentoses (5 carbons) and
hexoses (6 carbons).
Aldotrioses
H–C=O
H – C – OH
CH2OH
D-Glyceraldehyde
H–C=O
H–C=O
H – C – OH
H – C – OH
CH2OH
D-Erythrose
H–C=O
H–C=O
H – C – OH
H – C – OH HO – C – H
H – C – OH HO – C – H
H – C – OH
H–C=O
HO – C – H
HO – C – H
H – C – OH
H – C – OH
H–C=O
H – C – OH
HO – C – H
HO – C – H
H – C – OH
H – C – OH
H – C – OH
H – C – OH
H – C – OH
CH2OH
CH2OH
CH2OH
CH2OH
CH2OH
D-Ribose
D-Xylose
D-Glucose
D-Mannose
D-Galactose
CH2OH
CH2OH
CH2OH
C=O
CH2OH
Dihydroxyacetone
CH2OH
CH2OH
CH2OH
C=O
C=O
C=O
H – C – OH
CH2OH
D-Erythrulose
C=O
HO – C – H
C=O
HO – C – H
H – C – OH
H – C – OH HO – C – H
H – C – OH
H – C – OH
H – C – OH
H – C – OH
H – C – OH
H – C – OH
CH2OH
D-Ribulose
CH2OH
D-Xylulose
CH2OH
D-Fructose
CH2OH
D-Sedoheptulose
Characters of Monosaccharides
1-Stereochemical Isomers of Monosaccharides:
 Isomerism: Isomers are compounds having the same
molecular formula i.e. same number of carbon, hydrogen ,
oxygen ,etc atoms per molecule, but different structural or
steric formulae.
 Asymmetric carbon atoms are those attached to four
different groups. All monosaccharides contain one or more
asymmetric carbon atoms except dihydroxyacetone.
2-Optical Activity
 Plane Polarized Light (PPL): It is light waves vibrating
in one plane. It is obtained by passing ordinary light
(vibrating in all planes) through a prism of pure CaCO3
( Nicol prism) , which reflects all vibrations except
those which are parallel to the base of the prism.
α
W
Light
source Unpolarized
light
Polarizer
Polarimeter
Polarized light
Sample tube containing
optically active compound
Analyzer
Observer
 Optical Activity: It is the ability of a substance to rotate the
plane polarized light.
 If the rotation is to the right (clockwise), it is termed
dextrorotation.For example, D-glucose which is
dextrorotatory.
 If the rotation is to the left (anti-clockwise), it is termed
levorotation. For example, D-fructose which is levorotatory.
 Optical activity depends on the presence of at least one
asymmetric carbon atom in the molecule.
 Accordingly, all monosaccharides are optically active except,
dihydroxyacetone (has no asymmetric carbon atoms).
Specific Rotation:
 Optical activity can be measured by a polarimeter.
 Each substance has its specific rotation, which is the
degree of rotation measured under specific conditions
e.g. D-glucose (+52.5°) and D-fructose (-92.3°).
3-Ring Structures of Monosaccharides
 For example, in solution, the functional aldehyde group of
glucose combines with hydroxyl group of 5th carbon atom. As
a result a 6 numbered heterocyclic pyranose ring structure
containing 5 carbons and one oxygen is formed. Similarly, a 5
numbered furanose ring structure is formed from fructose
when its keto group combines with hydroxyl group on 5th
carbon atom.
O
-C4
-C-
O
1
4
Furanose
3
2
Haworth
Formula
-C1
-C-C-C
-C-5
-C-
5
O
4
O
-C1
-C-C-
1
3
2
Haworth
Pyranose Formula
 In either case, a new asymmetric carbon is created by the
reaction and we refer to the carbon as the anomeric
carbon and the two possible configurations as anomers.
 Cyclization creates a carbon with two possible
orientations of the hydroxyl around it (-form and βform). The -form (-OH is to the right of the anomeric
carbon) and the β- form (-OH is to the left of the
anomeric carbon)
5
OH
H
H
4
OH
O
6
H
OH
6
1
CH2OH
HOH2C
5
2
3
H
-D-Fructopyranose
OH

O
H
H
H
4
OH 
OH
2
CH2OH
3
1
OH
H
-D-Fructofuranose
Mutarotation
 It is the spontaneous change in specific rotation of an
optically active substance when a freshly prepared
solution is left to stand.
 When  or β forms of D-glucose are dissolved in water,
the optical rotation of each gradually changes with time
and reaches a final value of +52.5°. This change is called
mutarotation , which is due to the formation of an
equilibrium mixture consisting of about one third of D-glucose (+110°) and two thirds of β-D-glucose (+17.5°)
at 20°C.
α-D-Glucose
(+110°)
D-Glucose
β-D-Glucose
(+17.5°)
4-Reducing power:
 All monosaccharides are reducing agents in vitro.
 They reduce metallic ions in alkaline media.
 Cupric ions of Fehling or Benedicts solutions are
reduced to cuprous compound in alkaline media.
 The reducing property of sugars is strictly related to
existence of free carbonyl group.
Monosaccharide Derivatives
1- Sugar acids:
a- Aldonic acids:
The aldehyde group of aldoses is oxidised to form the
corresponding aldonic acid. Glucose is oxidised to form
gluconic acid
b- Uronic acids :
The primary alcohol group of monosaccharides is oxidised to
form the corresponding uronic acid. Glucose is oxidised to
form glucuronic acid (GlcUA).
c- Aldaric acids:
These are monosaccharides in which both the aldehyde and
primary alcohol groups are oxidised to form the
corresponding aldaric acid e.g. glucose gives glucaric acid.
 2- Sugar Alcohols:
 These are sugars in which the carbonyl group is
reduced to alcohol group. Sorbitol is the alcohol of
glucose, Dulcitol is the alcohol of galactose and
mannitol is the alcohol of mannose.
CH2OH
CH2OH
C=O
HO – C – H
CH2OH
H – C – OH
Reduction
HO – C - H
HO – C – H
HO – C – H
+
H – C – OH
H – C – OH
H – C – OH
H – C – OH
H – C – OH
CH2OH
CH2OH
CH2OH
D-Fructose
D-Sorbitol
H – C – OH
D-Mannitol
3- Deoxysugars :
These are sugars in which an –OH group is replaced by a
hydrogen atom e.g. 2-deoxy ribose: It is present in the
structure of DNA.
4- Aminosugars :
These are sugars in which an amino group (NH2) replaces the
–OH group on the second carbon e.g. glucosamine (GluN
5- Aminosugar acids :
These are formed by the addition of acids to aminosugars.
Addition of pyruvic acid to mannosamine gives neuraminic
acid.
II- DISACCHARIDES
 Disaccharides consist of two monosaccharides united
together by glycosidic linkage.
 If the glycosidic linkage involves the carbonyl group of
both sugars (e.g. sucrose) the resulting disaccharide is
non-reducing.
 On the other hand, if the glycosidic linkage involves the
carbonyl group of one of its two sugars (e.g. lactose and
maltose ) the resulting disaccharide is reducing.
A- Reducing disaccharides
These are disaccharides which have a free anomeric carbon in
the second sugar unit:
1. Maltose ( Malt sugar):
It is formed of two molecules of glucose united by 
glycosidic linkage.
3. Cellobiose :
It is similar to maltose but the linkage is β-glycosidic. It
results from the hydrolysis of cellulose.
4. Lactose ( Milk sugar):
It is formed of galactose and glucose united by β
glycosidic linkage.
B- Non –Reducing Disaccharides
Sucrose (Cane sugar) (Table sugar):
 It is present in plants as sugar cane and beets.
 It is formed of fructose and glucose united by β
glycosidic linkage Both anomeric carbons are involved in
the linkage, so sucrose is non-reducing.
 Sucrose is dextrorotatory (+66.5°), and on hydrolysis it
gives a levorotatory mixture of equal amounts of D-glucose
(+52.5°) and D-fructose (-92.3°).
 This mixture is termed invert sugar due to the inversion of
the rotation of the solution from dextro to levo, so the
enzyme is termed invertase or sucrase.
III- OLIGOSACCHARIDES
 These are polymers of 3-10 monosaccharide units.
 They are present as a constituent of many types of
glycolipids and glycoproteins e.g. oligosaccharides
which are constituent of ABO blood group substance,
immunoglobulins and glycolipids and glycoproteins of
cell membranes.
IV- POLYSACCHARIDES
 Polysaccharides are composed of more than 10
monosaccharide units linked by glycosidic bonds.
 Since the condensation of the monosaccharide units
involves the carbonyl groups of the sugars, leaving only
one free carbonyl group at the end of a big molecule,
polysaccharides are nonreducing.
 Polysaccharides include homo-polysaccharides and
heteropolysaccharides.
A- Homopolysaccharides
These are polysaccharides which are entirely made up of only one
type of monosaccharide units.
1- Starch :
Starch is the chief storage form of carbohydrates in chlorophyll –
containing plants. It is present in large amounts in cereals (rice
and wheat), tubers (potatoes and sweet potatoes) and legumes
(beans).
2- Dextrins:
They are produced during the hydrolysis of starch by salivary or
pancreatic amylase.
3- Glycogen:
 Glycogen is the storage form of carbohydrates in
animals (animal starch).
 It is mainly present in skeletal muscles and liver. It
is a highly branched homopolysaccharide.
4- Cellulose:
 Cellulose forms the principal part of the cell wall of
plants.
 It is formed of a long non-branched chain of β-Dglucose units connected together by β1,4-glucosidic
linkage.
 The presence of cellulose in diet is important as it
increases the bulk of food, which stimulates intestinal
contractions and prevents constipation.
B – Heteropolysaccharides
 These are polysaccharides which are formed of more than
one type of monosaccharide unit.
 They include glycosaminoglycans (GAGs) formly called
mucopolysaccharide.
Glycosaminoglycans (GAGs)
heteropolysaccharides composed of repeating disaccharide
units, usually made up of an amino sugar and a uronic acid.
Glycosaminoglycans are classified into:
I- Sulfate free glycosaminoglycans: e.g. hyaluronic
Acid-[(D-glucuronic acid)—(N-acetyl-Dglucosamine)]n
II- Sulfate containing glycosaminoglycans: e.g.
chondroitin sulphate, keratan sulphate, dermatan
sulphate, heparin and heparan sulphate.
 Functions and Importance of GAGs and
proteoglycans:
 GAGs present in proteoglycans are polyanions (highly
negatively charged due to the presence of the carboxyl
and /or sulfate groups) and can bind greatly with cations
like Na+ and K+, which attract water by osmotic pressure
into the extracellular matrix producing its swelling.
 Both characters offers viscid and resilience capability of
intracellular ground substance, synovial fluid of joints,
and vitreous humor of the eye globe.
Glycoproteins
They are proteins to which oligosaccharide chains are
covalently bound. The carbohydrate contents of
glycoproteins are less relative to proteoglycans and
deficient of uronic acids and the repeating
disaccharide units of proteoglycans.
ABO blood group antigens
The human blood groups A, B, AB, and O depend on the
oligosaccharide part of the a glycoprotein or a glycolipid
on the surface of erythrocyte cells.